Explorando A Volatilidade Médica Mover Ponderada Exponencialmente é a medida mais comum de risco, mas vem em vários sabores. Em um artigo anterior, mostramos como calcular a volatilidade histórica simples. (Para ler este artigo, consulte Usando a volatilidade para avaliar o risco futuro.) Usamos os dados atuais do preço das ações da Googles para calcular a volatilidade diária com base em 30 dias de estoque de dados. Neste artigo, melhoraremos a volatilidade simples e discutiremos a média móvel ponderada exponencialmente (EWMA). Vs históricos. Volatilidade implícita Primeiro, colocamos essa métrica em um pouco de perspectiva. Existem duas abordagens amplas: volatilidade histórica e implícita (ou implícita). A abordagem histórica pressupõe que o passado é o prólogo que medimos a história na esperança de que seja preditivo. A volatilidade implícita, por outro lado, ignora o histórico que resolve para a volatilidade implícita nos preços de mercado. Espera que o mercado conheça melhor e que o preço de mercado contenha, mesmo que de forma implícita, uma estimativa consensual da volatilidade. (Para leitura relacionada, veja Os Usos e Limites da Volatilidade.) Se nos concentrarmos apenas nas três abordagens históricas (à esquerda acima), eles têm dois passos em comum: Calcule a série de retornos periódicos Aplicar um esquema de ponderação Primeiro, nós Calcule o retorno periódico. Isso geralmente é uma série de retornos diários, em que cada retorno é expresso em termos compostos continuamente. Para cada dia, tomamos o log natural da proporção dos preços das ações (ou seja, preço hoje dividido por preço ontem e assim por diante). Isso produz uma série de retornos diários, de u i to u i-m. Dependendo de quantos dias (m dias) estamos medindo. Isso nos leva ao segundo passo: é aqui que as três abordagens diferem. No artigo anterior (Usando o Volatility To Gauge Future Risk), mostramos que sob um par de simplificações aceitáveis, a variância simples é a média dos retornos quadrados: Observe que isso resume cada um dos retornos periódicos, então divide esse total pelo Número de dias ou observações (m). Então, é realmente apenas uma média dos retornos periódicos quadrados. Dito de outra forma, cada retorno quadrado recebe um peso igual. Então, se o alfa (a) é um fator de ponderação (especificamente, um 1m), então uma variância simples parece algo assim: O EWMA melhora a diferença simples. A fraqueza dessa abordagem é que todos os retornos ganham o mesmo peso. O retorno de Yesterdays (muito recente) não tem mais influência na variação do que o retorno dos últimos meses. Esse problema é corrigido usando a média móvel ponderada exponencialmente (EWMA), na qual os retornos mais recentes têm maior peso na variância. A média móvel ponderada exponencialmente (EWMA) apresenta lambda. Que é chamado de parâmetro de suavização. Lambda deve ser inferior a um. Sob essa condição, em vez de pesos iguais, cada retorno quadrado é ponderado por um multiplicador da seguinte forma: por exemplo, RiskMetrics TM, uma empresa de gerenciamento de risco financeiro, tende a usar uma lambda de 0,94 ou 94. Neste caso, o primeiro ( Mais recente) o retorno periódico ao quadrado é ponderado por (1-0,94) (94) 0 6. O próximo retorno ao quadrado é simplesmente um múltiplo lambda do peso anterior neste caso 6 multiplicado por 94 5,64. E o peso do terceiro dia anterior é igual (1-0,94) (0,94) 2 5,30. Esse é o significado de exponencial em EWMA: cada peso é um multiplicador constante (isto é, lambda, que deve ser inferior a um) do peso dos dias anteriores. Isso garante uma variação ponderada ou tendenciosa em relação a dados mais recentes. (Para saber mais, confira a Planilha do Excel para a Volatilidade dos Googles.) A diferença entre a simples volatilidade e o EWMA para o Google é mostrada abaixo. A volatilidade simples efetivamente pesa cada retorno periódico em 0.196 como mostrado na Coluna O (tivemos dois anos de dados diários sobre o preço das ações. Isso é 509 devoluções diárias e 1509 0.196). Mas observe que a coluna P atribui um peso de 6, então 5.64, depois 5.3 e assim por diante. Essa é a única diferença entre variância simples e EWMA. Lembre-se: depois de somar toda a série (na coluna Q), temos a variância, que é o quadrado do desvio padrão. Se queremos volatilidade, precisamos lembrar de tomar a raiz quadrada dessa variância. Qual é a diferença na volatilidade diária entre a variância e EWMA no caso do Googles. É significativo: a variância simples nos deu uma volatilidade diária de 2,4, mas a EWMA deu uma volatilidade diária de apenas 1,4 (veja a planilha para obter detalhes). Aparentemente, a volatilidade de Googles estabeleceu-se mais recentemente, portanto, uma variação simples pode ser artificialmente alta. A diferença de hoje é uma função da diferença de dias de Pior. Você notará que precisamos calcular uma série longa de pesos exponencialmente decrescentes. Nós não vamos fazer a matemática aqui, mas uma das melhores características do EWMA é que toda a série se reduz convenientemente a uma fórmula recursiva: Recursiva significa que as referências de variância de hoje (ou seja, são uma função da variância dos dias anteriores). Você também pode encontrar esta fórmula na planilha e produz exatamente o mesmo resultado que o cálculo de longo prazo. A variação de hoje (sob EWMA) é igual a variância de ontem (ponderada por lambda) mais retorno quadrado de ontem (pesado por menos a lambda). Observe como estamos apenas adicionando dois termos em conjunto: variância ponderada de ontem e atraso de ontem, retorno quadrado. Mesmo assim, lambda é o nosso parâmetro de suavização. Um lambda mais alto (por exemplo, como RiskMetrics 94) indica decadência mais lenta na série - em termos relativos, teremos mais pontos de dados na série e eles vão cair mais devagar. Por outro lado, se reduzirmos a lambda, indicamos maior deterioração: os pesos caem mais rapidamente e, como resultado direto da rápida deterioração, são usados menos pontos de dados. (Na planilha, lambda é uma entrada, para que você possa experimentar sua sensibilidade). Resumo A volatilidade é o desvio padrão instantâneo de um estoque e a métrica de risco mais comum. É também a raiz quadrada da variância. Podemos medir a variação historicamente ou implicitamente (volatilidade implícita). Ao medir historicamente, o método mais fácil é a variância simples. Mas a fraqueza com variância simples é que todos os retornos recebem o mesmo peso. Então, enfrentamos um trade-off clássico: sempre queremos mais dados, mas quanto mais dados temos, mais nosso cálculo será diluído por dados distantes (menos relevantes). A média móvel ponderada exponencialmente (EWMA) melhora a variação simples ao atribuir pesos aos retornos periódicos. Ao fazer isso, podemos usar um grande tamanho de amostra, mas também dar maior peso aos retornos mais recentes. (Para ver um tutorial de filme sobre este tópico, visite a Tartaruga Bionica.) FISIOLOGIA amplificador CIÊNCIAS RELACIONADAS - UM CURTO GLOSSÁRIO A. R. Gardner-Medwin (UCL), N. Curtín, (Imperial), P. Tatham (UCL) copy 1990-2001 As palavras em ciência são muitas vezes usadas de diferentes maneiras do inglês comum. Os significados completamente diferentes ocorrem mesmo em diferentes ramos da fisiologia, e. Para a palavra acomodação. Como estudante, é fácil desesperar. Mas os significados das palavras são muito precisos na ciência: se você não os entender, ou se você usá-los casualmente, não será capaz de estudar de forma eficiente, e você não obterá boas notas. Este glossário é para navegar, testar-se e aprender sobre palavras que chamam sua atenção. Pare e leia sempre que tiver dúvidas ou interesse. Também, é claro, é um lugar para procurar palavras que você conhece e não entende. Mas é muito seletivo. Você também precisa de um dicionário em inglês e de um dicionário científico ou médico. Muitas palavras que você acha que você entende OK, você pode achar que não usou bastante como você pensou que este glossário concentra-se em palavras que muitas vezes causam confusão, especialmente nas ciências básicas (física, química e matemática) que são o fundamento da fisiologia. Você não precisa entender tudo, mas quanto mais você entender, mais fácil será aprender mais. Muitas vezes, é esperado nos exames para explicar o significado das palavras: pratique fazê-lo. Um breve glossário de termos médicos - Dissecado, Definido e Explicado também está disponível. Sugestões, correções, adições: clique ou envie um e-mail para a. gardner-medwin ltagt ucl. ac. uk a - Prefixo, geralmente equivalente a ab-, ad - ou an-. Abscissa RELACIONADO: eixos X, Y CONVERSE: ordenada 9830 eixo X, eixo horizontal. Geralmente, é mais simples e claro dizer eixo horizontal, já que a maioria das pessoas tem que parar de pensar em que abdutor de abcessa significa. Como auxílio à memória: Abscissa-Ordinate, X-Y, Horizontal-Vertical estão todos em ordem alfabética. Período refratário absoluto O tempo dentro de um período refratário durante o qual nenhum estímulo, por mais grande que seja, pode provocar um segundo potencial de ação de um tecido excitável. Absorção Transferência de substâncias para o corpo ou dentro do sangue, geralmente em uma superfície epitelial. Por exemplo. Absorção através da pele ou do intestino, ou reabsorção de substâncias do lúmen dos túbulos no rim. Espectro de absorção Gráfico da proporção de luz incidente (ou outra radiação) absorvida por uma substância em função do comprimento de onda, freqüência ou energia. Aceleração Taxa de mudança de velocidade. Observe que todas as partes de um objeto rotativo estão acelerando (exceto no eixo), mesmo que a rotação esteja estável: a aceleração é 4960 2 f 2 r onde f é a freqüência de rotação e r é o raio do eixo. As acelerações às vezes são expressas em relação à aceleração livre devido à gravidade (1g9,81 m. s -2). A aceleração é detectada no homem em grande parte pelos labirintos. Aclimatação, aclimatação O processo de adaptação a um novo ambiente, por exemplo, com temperatura ambiente alterada, pressão ou (com animais aquáticos) salinidade. A aclimatação às vezes é usada especificamente para significar adaptação a um único fator alterado (como em condições de laboratório). Acomodação RELACIONADO: adaptação 9830 Um processo de ajuste a novas condições. Usado em vários sentidos: 1. Atenuação ou ausência de resposta quando um estímulo é aplicado lentamente (por exemplo, falha na detecção de um cheiro quando ele se acumula lentamente ou falha em uma despolarização lenta para dar um potencial de ação). NB: isso é distinto da adaptação, mas muitas vezes é visto nos mesmos sistemas. 2. Ajuste do foco do olho. Acumulação progressiva de uma substância, etc. As toxinas cumulativas são absorvidas, mas não excretadas, para as quais é a dose total durante um período prolongado que importa em vez de o nível de exposição em qualquer momento. Precisão da medida RELACIONADA: resolução 9830 Os limites de confiança em um parâmetro, com base na sua medição. A precisão é limitada, em primeiro lugar, pela capacidade de um sistema de medição para distinguir diferentes condições (resolução) e, em segundo lugar, pela sua capacidade de relacionar as condições corretamente com um padrão (calibração). As duas considerações não devem ser confundidas. Um instrumento de alta resolução que fornece leituras estáveis e sensível a pequenas mudanças pode, no entanto, ser completamente impreciso se não for adequadamente calibrado. A precisão geralmente não pode ser maior do que a resolução de uma medida, exceto em circunstâncias especiais (por exemplo, onde uma leitura digital muda entre valores adjacentes e pode ser possível concluir que o valor está próximo de um passo incremental). Ácido CONVERSE: base 9830 Uma solução aquosa com um pH inferior a 7,0. Uma molécula ou íon que pode dissociar para liberar um próton (H). Por exemplo, H 2 CO 3 e H 2 PO 4 - são ambos ácidos. Acidose CONVERSE: alcalose 9830 pH anormalmente baixo do sangue. Uma condição acidótica pode ser capaz de ser restaurada ao equilíbrio ácido-base normal, aumentando a ventilação respiratória para reduzir o teor de CO 2 do corpo (acidose respiratória), ou pode requerer retenção ou injeção de HCO 3 - (acidose metabólica). Equilíbrio ácido-base Controle dos fatores que influenciam o pH do sangue. Os principais fatores sob controle homeostático são a excreção de CO 2. HCO 3 - e NH 4. Os distúrbios são diminuídos a curto prazo por vários sistemas de tampão de pH. As influências que afetam o pH do sangue são alterações na absorção, metabolismo e respiração e distúrbios que afetam os sistemas de controle. Acústico RELACIONADO: auditivo 9830 Relacionado a ondas sonoras ou sonoras. Potencial de ação ABBREV: pico 9830 Uma mudança de tensão transitória registrada dentro ou perto de um nervo, músculo esquelético ou outra célula excitável, devido a uma mudança característica do potencial da membrana. Os potenciais de ação ocorrem espontaneamente ou como reações de estimulação sem codificação de todas ou nenhuma frequência. A fase ascendente (despolarizante) é devida a canais de membrana dependentes de tensão que permitem o influxo passivo de Na ou Ca. A fase de queda é devida ao efluxo K passivo. Os picos de sódio são breves (cerca de 1 a 2 ms de comprimento), os pontos de cálcio são mais prolongados. Os potenciais de ação gravados extracelularmente podem ser pequenos (lt1mV), enquanto as mudanças de tensão através da membrana podem ser de gt100mV. Um potencial de ação composto é uma gravação extracelular do efeito combinado de potenciais de ação em muitas células. Ativação O processo de iniciar ou aumentar a atividade de algum tipo. Na fisiologia muscular, a ativação geralmente significa a indução de potenciais de ação na membrana celular (excitação) ao invés do início da tensão (NB, a ligação entre os dois é acoplamento excitação-contração). Energia de ativação RELACIONADA: Parcela de Arrhenius 9830 A energia necessária para atingir um estado intermediário em uma reação química. Uma alta energia de ativação diminui a taxa de uma reação em proporção a e-ART de acordo com a equação de Arrhenius. Um catalisador reduz a energia de ativação. Ativo CONVERSE: passivo, inativo 9830 1. Requer energia: e. Transporte ativo versus transporte passivo. 2. Fazendo algo: e. Uma fibra nervosa ativa, passando por potenciais de ação. 3. (Em vez de um confuso vago confuso, melhor evitado) vigoroso, importante: e. O dióxido de carbono desempenha um papel ativo na respiração. 4. Eficaz: E. g. Um ingrediente ativo. Local ativo da parte de uma célula ou de um receptor que se liga a um substrato. Transporte ativo RELACIONADO: transporte intermediário transportador 9830 Movimento líquido de uma substância em uma membrana de uma concentração mais baixa para uma maior ou (no caso dos íons) contra um gradiente eletroquímico. Isso requer energia, e pode ocorrer por ligação do transporte mediado pelo portador a um processo que fornece energia, como a hidrólise do ATP ou o movimento de declive de outra substância. Atividade RELACIONADA: concentração 9830 1. O estado de fazer algo: E. g. Potenciais de ação, secreção, movimento de acordo com os tecidos. 2. (Em química) um parâmetro semelhante à concentração, que determina a taxa em que as reações ocorrem. A relação entre atividade e concentração é o coeficiente de atividade, geralmente inferior a 1 devido a interações moleculares na solução que interferem com as reações. Acuidade Capacidade de identificar detalhes finos em um padrão sensorial. A acuidade visual depende do nível de luz, e é mais alta na fóvea. Geralmente, é medido clinicamente pela habilidade de discriminar letras em um Gráfico de Snellen: uma acuidade de 624 significa que um indivíduo pode apenas ler letras a 6m de distância que uma pessoa com acuidade nominalmente normal poderia simplesmente ler às 24m. A acuidade somatossensorial varia acentuadamente sobre a superfície do corpo e pode ser medida pela separação necessária para identificar que a pele está sendo tocada em dois pontos. Agudo CONVERSE: maçante, crônico 9830 Afiado, grave, de curta duração ou de início súbito. Um pouco ambíguo. Por exemplo. Dor aguda, fase aguda de uma resposta (geralmente uma parte de uma resposta grande e de curta duração). Uma experiência aguda é aquela em que um animal é anestesiado no início e eventualmente morto antes de recuperar a consciência. AC acoplado RELACIONADO: DC-acoplado, filtro, off-scale 9830 Uma gravação que é sensível às mudanças no parâmetro medido, mas não ao seu nível estável. Útil se as mudanças são de interesse, e um nível de fundo grande ou variável significa que o registro seria desabafado. A transição entre o que é e não está gravado caracteriza-se por uma frequência de corte, abaixo da qual os sinais são severamente atenuados (por mais de um fator de 2 em energia). Alguns circuitos acoplados a CA são caracterizados por uma constante de tempo, onde o retorno à linha de base após uma mudança de nível de entrada é exponencial. O acoplamento AC introduz a distorção de sinais que possuem componentes de freqüência em torno ou abaixo da freqüência de corte. Ad-Towards, ao lado. Adaptação Declínio de uma resposta enquanto um estímulo é mantido constante após o início. Distinguir cuidadosamente da acomodação e habituação. A adaptação clara e escura é o processo de ajuste do olho a diferentes níveis de luz (seja rápido ou lento). Estímulo adequado A forma de estimulação que normalmente provoca uma reação específica, como um potencial de ação ou uma resposta reflexa. Adrenalina, epinefrina (EUA) Um hormônio liberado juntamente com a noradrenalina da medula adrenal, especialmente em condições de estresse. Atua nos receptores adrenérgicos alfa e beta e simula alguns dos efeitos da ativação do nervo simpático. Adrenérgico relacionado à adrenalina ou à noradrenalina. As fibras adrenérgicas liberam a noradrenalina, enquanto os receptores adrenérgicos alfa e beta ligam adrenalina, noradrenalina e outros agonistas adrenérgicos. Adulto sexualmente e emocionalmente maduro. Aequorina Uma proteína natural extraída de água-viva (Aequorea aequorea) que emite luz na presença de íons ATP e Ca. Usado experimentalmente para medir as concentrações de Ca dentro das células. CONVERSO aeróbico: anaeróbio 9830 Envolvendo o uso de oxigênio. As condições aeróbicas são aquelas em que O 2 está presente. Etiologia, etiologia (EUA) A causa de uma doença. Efeito RELACIONADO: efeito 9830 Afeta e efeito geralmente causam problemas. O efeito é um verbo que significa alterar, p. O sal afeta o sabor da comida. O efeito é um significado que significa conseqüência, e. O sal tem muitos efeitos fisiológicos. O plano mais simples é aprender um amplificador em relação a esses significados. No entanto, o efeito também pode ser um verbo, o que significa produzir, e. O sal atinge uma redução no fluxo de urina. Note-se que é verdade dizer que o sal afeta a produção de urina, mas é falso dizer que a produção de urina de efeitos salinos (faz exatamente o contrário). Tenha cuidado Uma última complicação é que o efeito é um substantivo técnico em psicologia, que significa humor. É mesmo verdade que os sais de lítio têm efeitos que afetam o afeto: a depressão clínica é um transtorno afetivo para o qual o lítio pode fornecer um tratamento eficaz, embora, infelizmente, raramente eleva uma cura permanente. Afectivo Relativo à emoção ou humor. Aferente CONVERSE: eferente 9830 Viajando ou transportando algo em direção a uma estrutura, ou relacionado a suas entradas. Os nervos aferentes ou os potenciais de ação são geralmente aqueles que viajam para o sistema nervoso central. Os navios afferentes transportam fluidos para um órgão ou tecido especificado. Arteríola aferente Arteríolos transportando sangue em direção a um órgão estrutural, como os glomérulos renais, em que há controle arteriolar de vasos aferentes e eferentes. Afinidade A força da ligação de dois produtos químicos, ou um produto químico ou íon para um receptor ou enzima. A afinidade de um receptor para um agonista pode ser expressa pela concentração agonista na qual metade dos receptores são ligados a moléculas agonistas (a constante de dissociação para o complexo: KD), ou por log 10 dessa quantidade ou por seu recíproco. Pós-descarga Potenciais de ação que ocorrem após a cessação de um estímulo ou uma ação voluntária. Agonista CONVERSE: antagonista 9830 Algo que auxilia ou imita uma ação. Por exemplo, os músculos agonistas puxam partes do esqueleto na mesma direção. Agonistas ou substâncias químicas se ligam aos mesmos receptores, produzindo os mesmos efeitos. Algoritmo Um conjunto de regras para resolver um problema. Isso geralmente é expresso em um programa de computador. Alimentar Relativo aos alimentos, ou o trato gastrointestinal. All-or-none RELACIONADO: limiar, feedback positivo CONVERSE: graduado 9830 Uma resposta que aparece apenas se a força de um estímulo exceder algum nível limiar, mas cuja amplitude e características não dependem do estímulo, p. Um potencial de ação, ou um espirro. O espirro é mais familiar: a pimenta faz ou não leva a um espirro. Um pouco de pimenta não leva a um pequeno espirro, embora possa levar a menos espirros. Isso não quer dizer que os espirros sejam sempre idênticos: você pode sufocar um espirro e, por exemplo, reduzir o ruído que ele faz. Essas alterações não são nada a ver com o estímulo que causou o espirro, no entanto. As coisas exatamente paralelas são verdadeiras para os potenciais de ação. As respostas de todos ou nenhuns geralmente envolvem alguma forma de feedback positivo. Radiação alfa ABBREV: raios 945 9830 Núcleos de hélio emitidos durante a desintegração de alguns elementos radioativos. Altitude Altura acima do nível do mar. Isso afeta processos fisiológicos em grande parte através da pressão atmosférica reduzida, que cai exponencialmente até ca. 12 por 1000m de aumento (18 por 5000 pés). A porcentagem de oxigênio no ar inspirado permanece constante (aproximadamente 21). Os efeitos da altitude são frequentemente estudados por simulação em uma câmara com pressão reduzida. A respiração é afetada visivelmente a 4000 m (13,000 pés) e severamente aos 6000 m (20,000 pés). O PO 2 reduzido leva à hiperventilação, que mantém parcialmente o PO 2 arterial, mas reduz a PCO 2 arterial. Ar alveolar, ar que está ou esteve nos alvéolos. Amostras de ar alveolar podem ser tomadas no final da expiração após o ar do espaço morto ter sido expulso (amostras de maré final). O ar alveolar está normalmente aproximadamente em equilíbrio com o sangue arterial e, portanto, tem aproximadamente as mesmas pressões parciais de O 2 e CO 2 como sangue arterial. Alveolus Os sacos de ar terminais nos pulmões, onde a troca de gás ocorre com o sangue. Tipicamente 150-300microm em diâmetro no homem (volume de aproximadamente 5nl). Ambiente Relativo ao meio ambiente de um animal. Por exemplo. Temperatura ambiente, pressão. Observe que as condições para um tecido específico podem ser diferentes das condições ambientais. Ampere ABBREV: A, amp 9830 Unidade de fluxo de corrente elétrica. Amplificação RELACIONADA: ganho CONVERSE: atenuação 9830 Aumento no tamanho de um sinal. Isso pode ser ativo (exigindo energia, como em um amplificador elétrico) ou passivo, como na amplificação do movimento que pode ser alcançado onde um músculo puxa uma alavanca. Quantitativamente, a amplificação é a proporção dos dois sinais. Amplitude Magnitude como é grande. Muitas vezes, pode ser definido de várias maneiras diferentes, e é importante especificar qual é a sua definição. Por exemplo, a amplitude de uma forma de onda sinusoidal ya. sin (wt) pode significar o coeficiente a nesta expressão, ou pode significar a amplitude de pico a pico (ou seja, a diferença de altura entre os máximos e mínimos na forma de onda (2a ), Ou pode significar a amplitude do quadrado médio (rms) (0.71a). O mesmo se aplica às medidas que você faz de uma amplitude de resposta, por exemplo, um potencial de ação: diga sempre como você está medindo (por exemplo, do descanso Potencial para o pico positivo) an - Sem, falta ana, aumentada anestesia RELACIONADA: parestesia, analgesia 9830 A ausência de sensação. Esta pode ser anestesia geral, caso em que o sujeito é inconsciente ou anestesia local que afeta a sensação De uma parte do corpo. A anestesia local pode ser devido à influência de um medicamento anestésico ou a um trauma nervoso, etc. analgesia Ausência de sensação de dor. Analógico RELACIONADO: graduado 9830 1. Variável continuamente. Um parâmetro analógico pode ter algum valor Dentro de um intervalo, eg temperatura corporal. Isso é contrário a um parâmetro digital, que só pode ter certos valores (talvez inteiros), e. O número de membros que um animal tem. Os números analógicos são aproximados em computadores por números digitais. 2. Uma droga semelhante a outra droga ou a um hormônio, etc. analítico RELACIONADO: numérico 9830 Os métodos analíticos para resolver problemas matemáticos empregam técnicas matemáticas para chegar a soluções explícitas, que podem ser usadas em instâncias mais ou menos gerais. Os métodos numéricos, pelo contrário, usam computadores para resolver problemas em casos específicos. Aneurisma Uma parte anormalmente abaulada de um vaso, geralmente uma artéria. NB: nada a ver com os nervos: deriva de ana até eurys de largura. Aringngstrom ABBREV: Aring 9830 Uma unidade antiga de comprimento: 10 -10 m ou 0.1nm. Velocidade angular Taxa de mudança de orientação de um corpo rotativo, geralmente medido em radianos. s -1 (caso em que a velocidade angular é de 2960 9830 de rotação. Anião CONVERSE: catião 9830 íon negativo. Os íons Negativos negativos se movem em direção a um ânodo ( Elétrodo positivo) em solução: daí a nomenclatura aparentemente confusa. Anisotropia Tendo diferentes propriedades em diferentes direções. Anel em forma de anel. A zona entre dois círculos concêntricos. Bloco anódico. Prevenção da propagação de potenciais de ação em uma região próxima a um ânodo, devido à hiperpolarização Anodo CONVERSE: cátodo 9830 Um eletrodo positivo. Na solução, os cations se afastam e aniões em direção a um ânodo, ambos contribuindo para o fluxo de corrente afastado do ânodo. Estimulação da ruptura do ânodo Iniciação de potenciais de ação próximos a um ânodo (onde a célula é hiperpolarizada Durante o fluxo de corrente), ocorrendo após a cessação do fluxo atual. Anômalo Inesperado, diferente da tendência principal dos resultados ou da Expectativa mineral. Anoxia A condição sem oxigênio. Antagonista CONVERSE: agonista 9830 Algo com o efeito oposto. Por exemplo. Um químico que se opõe à ação de outro químico, ou um músculo puxando na direção oposta. Ante - CONVERSE: pós-9830 Antes. Por exemplo. Pré-natal antes do nascimento. Anterior CONVERSE: posterior 9830 Perto ou mais próximo à frente. Anti RELACIONADO: contra-CONVERSE: ortho - 9830 Oposto, contra. Por exemplo. Direção antidromica oposta ao normal. Antilog RELATED: logarithm 9830 A função inversa de um logaritmo. É quase sempre usado para o inverso de logaritmos para a base 10. Neste caso, antilog (x) 10 x. Antor Cavity. Extremidade duodenal estreita do estômago (píloro). Aquático Associada à água. 1. Parte da circunferência de um círculo. 2. Um arco reflexo. Parcela de Arrhenius Um gráfico de uma taxa de reação contra 1T, onde T é a temperatura absoluta. Isso geralmente é linear, de acordo com a equação de Arrhenius, com uma inclinação de - EaR onde Ea é a energia de ativação e R a constante de gás. Artefato, artefato Algo que se origina incidentalmente do modo como um experimento é realizado e não relacionado ao objetivo principal do experimento. As experiências de controle são muitas vezes úteis na tentativa de identificar artefatos. Pressão arterial Pressão dentro de uma artéria, em relação à pressão atmosférica ambiente. Isso varia durante o pulso entre pressão sistólica (máximo) e pressão diastólica (mínimo). Também varia ao longo das artérias devido aos efeitos da pressão hidrostática e (especialmente nas artérias pequenas ou obstruídas) a resistência das artérias ao fluxo. Medidas clínicas padrão são normalmente feitas em uma grande artéria na mesma altura que o coração. Arteriole Porção terminal estreita de uma artéria, levando aos capilares. Navio de resistência. Site principal de controle do fluxo sanguíneo para os tecidos, através da inervação, quimiossensibilidade e sensibilidade térmica do músculo liso das paredes da arteríola. A constricção aumenta a resistência ao fluxo nas arteriolas. Observe que não aumenta diretamente a pressão dentro das arteriolas (uma má interpretação comum), uma vez que elas estão abertas nas duas extremidades. De fato, a constrição geralmente reduz a pressão na extremidade distal (capilar) das arteríolas, porque o fluxo sanguíneo através dos capilares é reduzido e a pressão capilar fica mais próxima da pressão venosa. Arteriosclerose Perda de elasticidade das artérias, geralmente devido ao envelhecimento e aterosclerose. Arterias arteriais arteriais e veias. A diferença de pressão arteriovenosa é a força motriz líquida que faz com que o sangue flua através de um tecido. Artéria, vasos de paredes espessas que transportam sangue a uma pressão relativamente alta longe do coração. As artérias pequenas são contrácteis, devido ao músculo liso presente na mídia da túnica. A elasticidade é importante para acomodar o sangue ejetado do coração durante a sístole sem aumento excessivo de pressão. - Enzima que quebra uma substância. Asíntota Uma linha direta que se aproxima, mas nunca é alcançada por um gráfico, geralmente como você vai muito ao longo de um ou outro eixo. Nem todas as funções dão asíntotas. Por exemplo, o gráfico de y1x aborda ambos os eixos, assintoticamente, o gráfico de yx1x se aproxima do eixo y e da linha yx. Nem yx 2 nem ysin (x) têm asíntotas. Tente esboçar esses gráficos, com suas assíntotas, quando aplicável. Assíncrono fora da sincronia, ou não ocorre em relação a um ritmo contínuo, como o ciclo cardíaco. Ar atmosférico A composição do ar fresco varia pouco, além do teor de água (0-7). O oxigênio é 21, N 2 78 e CO 2 0,03 de ar seco. O teor de CO 2 pode ser considerado como zero para todos os efeitos práticos na fisiologia animal. A pressão total (cerca de 10.1kPa, 760mmHg no nível do mar) é a soma das pressões parciais dos gases constituintes, incluindo pressão de vapor de água (pressão de vapor de água saturada de umidade relativa 9830). Peso atômico Massa média dos isótopos de ocorrência natural de um elemento, relativo a H como 1 ou O como 16. Os pesos atômicos dos elementos biologicamente importantes mais comuns são: H 1,0, C 12,0, N 14,0, O 16,0, Na 23,0, Mg 24.3, P 31.0, S 32.1, Cl 35.5 K 39.1, atenuação Ca 40.0 RELACIONADO: amplificação, ganho CONVERSE: amplificação 9830 Redução de tamanho ou efeito. Os sons estão atenuados com a distância. As alterações na pressão sanguínea durante o pulso são atenuadas em pequenas artérias. Um dispositivo de gravação pode ter um atenuador para permitir variar o ganho (ou amplificação geral). Atto - ABBREV: um RELACIONADO: unidades SI 9830 Um milhão milhões de milionésimos, 10 -18. Autonomico RELACIONADO: parassimpático, simpático 9830 Relativo ao sistema nervoso autônomo. Isso inerva músculo liso, glândulas e órgãos viscerais, que normalmente não estão sob controle voluntário. Subdividido principalmente nos sistemas eferentes simpáticos e parassimpáticos. Os reflexos autonômicos são reflexos que atuam através desses sistemas eferentes. Suas vias aferentes podem ser as mesmas que caminhos que subsistem percepções conscientes (como com a salivação) ou podem ser diferentes (como com reflexos de baroreceptor). As vias aferentes não são distintivas de nenhuma maneira anatômica, e geralmente não são descritas como autonômicas, exceto por associação com ações específicas de reflexos. Autorradiografia Localização de material radioativo em tecido pela aposição de filme ou incorporação de emulsão fotográfica no processamento histológico de tecido. Autoregulação Processo pelo qual um órgão rege diretamente as mudanças na sua resistência vascular de modo a controlar o fluxo sanguíneo, sem envolver o sistema nervoso central ou influências hormonais sistêmicas. Isso pode produzir uma porção relativamente plana do gráfico do fluxo contra a pressão arterial. Número de Avogadros 6,0 x 10 23 g -1. O número de átomos ou moléculas com uma massa, em gramas, igual ao seu peso atômico ou molecular. Princípio de Avogadros Os volumes iguais de gases diferentes contêm, nas mesmas condições de temperatura e pressão, o mesmo número de moléculas. Um corolário de relevância fisiológica mais direta é que a porcentagem de degradação de uma mistura de gases por volume (por exemplo, 21 O2 no ar normal) é a mesma que a porcentagem de degradação pelo número de moles ou moléculas dos gases constituintes. Uma mole de gás a 1atm de pressão ocupa 24 litros a 20 o C (22,4 litros a 0 o C). Assim, 1 litro de ar contém 42mmol de constituintes combinados a 20 o C, incluindo ca. 9mmol de O 2. Axon Uma fibra nervosa. Pode ser mielinizado ou não mielinado. Um nervo é constituído por muitos axônios, células de Schwann (células de apoio) e uma bainha. Equilíbrio Um controle de equilíbrio em um instrumento de medição (por exemplo, um amplificador de osciloscópio) permite que você ajuste o circuito interno do instrumento para uma operação ideal. Para ajustar o controle de equilíbrio de um osciloscópio, conecte a entrada do amplificador à terra e aumente gradualmente a sensibilidade do mínimo. Sem entrada (zero volts), você deve esperar que a gravação (ou seja, a altura do ponto ou do rastro) não mude com o aumento da sensibilidade. Se mudar, ajuste a balança e tente novamente com a sensibilidade mínima. Depois de ter feito isso, você não deve usar o controle de saldo para fazer ajustes se uma gravação escusar-se: você geralmente pode usar um controle de deslocamento ou deslocamento. Passagem de banda RELACIONADO: filtro, passagem alta, passagem baixa 9830 Um tipo de filtro que permite uma gama de freqüências e corta as freqüências mais altas e mais baixas. Uma passagem alta e um filtro de passagem baixa que atuam em série alcançarão isso, embora também possa ser alcançado em um único circuito. Um filtro de passagem de banda com uma banda de passagem estreita é equivalente a um filtro ressonante. Largura de banda RELACIONADO: resposta de freqüência 9830 O intervalo de freqüências ao qual um sistema irá responder, ou que é passado por um filtro. Gráfico de barras RELACIONADO: gráfico X-Y, histograma 9830 Um gráfico no qual as observações (normalmente ao longo do eixo vertical) são mostradas como barras em vez de como pontos. Isto é preferido se o eixo horizontal, separando diferentes condições experimentais, for qualitativo e não quantitativo. Por exemplo, as medições podem ser feitas com e sem fármaco ou lesão, ou em pacientes e indivíduos controle. Um histograma é um tipo especial de gráfico de barras, onde o eixo horizontal é quantitativo. SUF báltico relacionado à pressão. Por exemplo. Hiperbárica acima da pressão atmosférica. Base Em uma expressão da forma que você está. A é a base e b é o expoente. Correspondentemente, os logaritmos são definidos em relação a uma base específica. Na expressão ya b. B é o logaritmo para a base a de y. Na química, uma base é uma molécula ou íon que irá ligar íons de hidrogênio. Linha de base RELACIONADA: controle 9830 Período de gravação antes de um estímulo é dado. As gravações em uma experiência geralmente são inúteis, a menos que haja alguma gravação de linha de base, mostrando medidas razoavelmente estáveis. Uma resposta só vale a pena considerar se é maior que, ou pelo menos diferente de, flutuações de linha de base. Às vezes, é impossível obter medidas de linha de base: por exemplo, você geralmente não pode fazer medições de linha de base em pacientes antes de adoecer. Então você tem que confiar em assuntos de controle (por exemplo, pessoas que não estão doentes) para verificar se eles não mostram as mesmas mudanças quando você começa a fazer medições sobre eles. Ciências básicas Pesquisas realizadas sem o objetivo imediato de aplicar os resultados em um contexto tecnológico ou clínico. As descobertas que levam a aplicações extremamente importantes são muitas vezes feitas apenas como resultado da curiosidade científica de um pesquisador (por exemplo, descoberta de Faradays dos princípios da geração de energia elétrica ou descoberta de penicilina nos flemings). Há muito debate sobre a questão de saber se o progresso na aplicação útil da ciência é melhor encorajado ao colocar dinheiro em pesquisas aplicadas ou básicas. Bilhão Um número melhor evitado Normalmente significa 1012 ou 10 12 no Reino Unido e 109 ou 10 9 nos EUA e nos círculos financeiros. Ligue para isso mil milhões ou um milhão de milhões. Binário RELACIONADO: digital, decimal, octal, hexadecimal 9830 Tendo apenas 2 valores possíveis. Os números são representados nos computadores como seqüências de elementos binários: e. 2511001, correspondendo ao fato de que 25 1times16 1times8 0times4 0times2 1times1. Isto é essencialmente semelhante à convenção decimal familiar em que 25 significa 2x10 5x1. As frações também podem ser representadas em binário, e. 0.625 (decimal) 0.101 (binário), ou seja, 1times0.5 0times0.25 1times0.125. Birrefringência Anisotropia óptica de um material que leva a um índice de refração diferente para luz polarizada em diferentes direções. Cego RELACIONADO: duplo cego 9830 Um experimento no qual o experimentador ou o sujeito não tem conhecimento de algum aspecto das condições experimentais. Por exemplo, um ensaio pode ser feito cego, e a pessoa que o realiza não tem conhecimento da fonte de amostras individuais. Isso ajuda a eliminar o viés, ou seja, a possibilidade de idéias preconcebidas do experimentador afetando os resultados. Bloco 1. Na fisiologia e na farmacologia, o bloqueio geralmente significa parar alguma coisa acontecendo (por exemplo, um anestésico local bloqueia potenciais de ação em fibras nervosas), ou para diminuir (por uma ou outra maneira) a eficácia de um fármaco, e. Curare bloqueia a ação da acetilcolina na junção do nervo-músculo. 2. Um experimento com ensaios realizados em um bloco significa que os ensaios são próximos ao tempo, ou não intercalados com outros ensaios sob diferentes condições. Condições de contorno RELACIONADO: equações diferenciais 9830 As condições que determinam a forma particular de solução que terá uma equação diferencial. Às vezes, estas são condições em um limite físico, e. A borda de um pedaço de tecido. Às vezes, eles são condições em um momento ou lugar particular, como quando há um distúrbio local súbito. Por exemplo, a equação de difusão aplicada a uma região de tecido tem diferentes soluções, dependendo se a superfície é permeável e lavada por uma solução livre da substância difusora (c0 na superfície), ou é impermeável à substância (implicando fluxo zero e Gradiente de concentração perpendicular à superfície). Tampão RELACIONADO: pH 9830 Um mecanismo tampão torna os efeitos de um distúrbio menor do que seria de outra forma. As misturas particulares de produtos químicos podem amortecer a concentração de um íon, por exemplo, H ou Ca. A buffer for pH is a mixture of the protonated and unprotonated forms of a weak acid (e. g. H 2 PO 4 - and HPO 4 --. Addition of acid or base causes conversion between these two forms, binding (or releasing) hydrogen ions. This keeps the pH relatively constant. Buffers are most effective, for a given total concentration, when the pH is approximately equal to the pK of the reaction: the two forms of the buffer are then in equal (and therefore quite high) concentration. bug A mistake or problem, usually in a computer program. To debug is to remove such mistakes, while a debugger is a program that helps you to do this. bulk flow Flux of a solution as a whole, carrying all its solutes. cable equation The partial differential equation governing the spread of current and voltage along electric cables and cell membranes. If V is disturbance of membrane potential from rest, T the membrane time constant and 923 the electrotonic length constant for the cell, then dVdt(923 2 d 2 Vdx 2 - V)T (away f rom the site of a disturbance). Solutions of this equation are set out in Jack, Noble amp Tsien (1975), for various boundary conditions and for cells coupled together to form syncytia. One important situation is where there is a local but relatively long lasting disturbance (e. g. at a synapse): the resulting shift of membrane potential falls off exponentially with an exponential length constant of 923. cable theory Mathematical description of the purely passive spread of electrical current in a cell. Similar to the theory necessary for understanding the properties of very long telephone cables. calci - Relating to calcium, E. g. hypercalcaemia calculus In mathematics, the methods for handling gradients, derivatives and integrals. Anatomically, a stone or hard deposit in tissue. calibration RELATED: accuracy 9830 Comparison of a measurement with a known standard. A set of standards are often required to construct a calibration curve: a graph of the output of a measuring system against the known values. An accurately linear measuring system permits interpolation between just two standards. calorie Unit of energy, particularly heat. 1 calorie 4.18 Joules. The Calorie of nutrition, in a non-scientific context, is unfortunately usually 10 3 calories. However, kcal on a food packet will correctly mean 10 3 cal, not 10 6 cal. Best to avoid this unit (not strictly part of S-I units) when possible, and use Joules. cannula RELATED: catheter 9830 A tube inserted into a vessel (usually a blood vessel) through its wall, so that solution can be put into or withdrawn from the vessel. capacitance Physiological capacitance vessels in the circulation are ones that can contain an extra volume of blood with little or no increase in pressure (mainly the veins, which are like floppy tubes). Electrical capacitance is related: electrical charge is like an amount of electrical substance, and voltage is like pressure. The capacitance between places A and B is the amount of charge you can shift from A to B per unit of voltage change between A and B. A large capacitance (measured in farads: CoulombsVolt) means you need a lot of charge to get much of a voltage shift. Myelinated nerve fibres conduct faster, largely because the myelin reduces the capacitance of the axon. cardiac Relating to the heart, or (as in cardiac sphincter) to the top end of the stomach. carrier RELATED: channel 9830 In the context of membrane transport, a protein that binds a specific substance and by changing conformation transports the substance to the other side of the membrane. A carrier is very much like an enzyme. Carriers are involved in facilitated diffusion, in which the net flux is always down an electrochemical gradient, and also in active transport. Some carriers move two substrates at once. catabolism Metabolism involving the destruction or disappearance of tissue. Fat stores, and ultimately muscle tissue, are catabolised in starvation. catheter RELATED: cannula 9830 Tube inserted into a narrow opening so that fluid can be removed or introduced. You might sometimes insert a catheter through a cannula. cation CONVERSE: anion 9830 Positive ion. caudal CONVERSE: rostral 9830 Toward the tail end of the animal. causal factor Something that contributes to the probability of occurrence of something else, but does not always cause it. centi - ABBREV: c RELATED: SI units 9830 One hundredth 10 -2. Seldom used, except in the unit cm (10mm). cerebral Relating to the brain. cervical Relating to the neck, or the neck of the uterus (womb). cgs RELATED: mks 9830 A system of units based on the centimetre, gram and second. This used to be the commonest standard in the UK, but was replaced some years ago by the SI system, which uses mks units. channel RELATED: permeability, carrier 9830 In membrane transport, a protein that spans the cell membrane and allows substances (usually ions) to move across the membrane. A conformational change in the protein is not involved for each ion that moves, unlike with a carrier. Much higher fluxes can occur than with carriers, and channels are mainly responsible for the permeability of most membranes. Many channels are gated, i. e. can be opened or closed, e. g. as a result of binding of transmitters, hormones or intracellular messengers, or as a result of changes of membrane potential. Different channels also have different selectivities for the ions they let through. Single isolated ion channels can be studied with patch techniques. chaos RELATED: turbulence 9830 A recently developed branch of mathematics, dealing with systems that obey well defined equations, but that are nevertheless intrinsically unpredictable in some respects. The solutions of the equations are very sensitive to the initial starting conditions, so that conditions that are very similar (perhaps within the resolution of any measuring system) can lead, after a short time, to completely different behaviour. It may be possible to predict the behaviour in statistical terms (e. g. the mean velocity of turbulent fluid flow), but not in detail. There are potential applications of chaos theory to the physiological understanding of irregular cardiac rhythms and neural networks. chronic RELATED: tonic CONVERSE: acute 9830 Continuous, or existing for a long time. circa ABBREV: ca.) 9830 Approximately. circadian rhythms RELATED: nocturnal, diurnal 9830 Cyclic patterns of behaviour or of tissue activity (e. g. hormone secretion) that repeat with a period of approximately 24 hours, even when organisms are isolated from the normal daily environmental changes. clamp To keep a parameter constant, or change it in a controlled way to a required value during an experiment. Usually the process involves a control system with negative feedback, which automatically adjusts the parameter if there is a discrepancy from its set value. A voltage clamp circuit is used to control the membrane voltage of a cell in order to study the effects of changes in membrane voltage. It usually requires two microelectrodes in the cell: one to measure the membrane potential, and the second to pass current into the cell to alter the membrane voltage (though sophisticated circuits can sometimes use a single electrode for both purposes). coefficient This is usually a number by which something is multiplied in an equation. For example, the area of a circle is proportional to the square of the radius, with a coefficient 960 (i. e. A960timesr 2 ). In much the same way, it is often used for a quotient (or ratio) of two things, expressing some characteristic property of a substance or an observation. For example the coefficient of variation of a measurement is its standard deviation divided by its mean value. cofactor A chemical in addition to the substrates (reactants) that must bind to an enzyme for a reaction to take place. compartment A definable part of the total volume of a tissue or organism. Por exemplo. blood plasma, intracellular or interstitial fluid compartments. competitive In considering the binding of substrates to receptors, enzymes or carriers, this means that two or more related substances are similar enough to bind to the same site. Consequently, the extent of binding of one will be reduced if the other is also present and binding to some of the sites. This can lead to competitive inhibition of a reaction or of the normal physiological effects produced by substrate-receptor binding. Many drugs (competitive antagonists) act in this way. compiler RELATED: interpreter 9830 A computer program that translates instructions written in a high level computer language into a form that can be used directly by a specific type of computer. Once a program has been written, the compiler only has to be used once to generate the machine code, usually in the form of an executable file that can then be used without the compiler. The translation process may take quite a long time, and must be repeated when mistakes are corrected in the original program or when changes are required. In these respects, the translation process is quite different from the use of an interpreter. complex A complex is a combination of several things, for example anatomical structures that occur together, or signs and symptoms that occur together in a disease. complex numbers ABBREV: xiy RELATED: vector 9830 A way of thinking about vectors (i. e. arrows) on a 2-dimensional plane as if they were represented by single (but complex) numbers. In an ordinary sense it takes 2 numbers to characterise an arrow: either its length (r) and orientation (952), or the displacements it produces in the x amp y directions. It turns out that the complex expressions xiy and rtimese i952 ), where i is an imaginary number that gives -1 when squared, follow exactly the same rules as vectors when added and multiplied. In handling vectors and sine waves (which correspond to the height of a rotating vector) it is often convenient to use these complex formulae and avoid the need to think in geometrical terms. compliance ABBREV: RELATED: stiffness 9830 A measure of how easily something complies with a force applied to it. For muscles tendons, etc. it is the increase in length divided by the increase of force applied to the structure (i. e. the gradient of the graph of length plotted against force). For the lungs, compliance is the increase of volume divided by the increase of pressure applied at the mouth to inflate the lungs. Stiffness is the reciprocal of compliance. concentration ABBREV: RELATED: activity 9830 The quantity of a solute per unit volume. It may be measured in gl, molsl, kgm 3. g100ml, etc. always with dimensions massvolume. Physiological concentrations are most often expressed in molsl (i. e. the molar concentration or molarity). The unit of molar concentration is 1moll, also written as 1M. Note that it is quite wrong to express a concentration either as 1mol, or 1Ml. These are NOT units of concentration Occasionally concentrations are expressed as , or parts per million (ppm), or gkg. These ratios usually mean the weight of solute per unit weight of solution, or (for a gas) the volume fraction within a mixture. may also mean g100ml. condenser In electricity: old-fashioned word for a capacitor. conductance The reciprocal of resistance. The unit of electrical conductance, the reciprocal ohm, is also called a mho or a Siemens (S). It is often more convenient to think about conductance than resistance. For example, the conductance of a membrane is proportional to its area and is characterised by a specific membrane conductance in S. m -2 . conductivity The reciprocal of resistivity. Units: 937 -1 m -1 or S. m -1 . confidence limits RELATED: significance 9830 The range of values within which you are confident that the true result lies, after doing an experiment. The mean result that you obtained will normally be around the middle of the range. Depending on how variable your individual results were, and how many results you obtained, you may need to assign a large or small range of uncertainty around this mean. 95 confidence limits indicate that if the true mean is outside these limits, the probability that your result would have come out as far away as it did from the true mean is less than 5. constant RELATED: variable 9830 A parameter that is always, and everywhere, the same within the experimental conditions under consideration, but whose value may be relevant to the results. For example the temperature of the Ringer solution might be a constant throughout a series of experiments on isolated muscle: when you describe the results you should state what it is, since it very likely might be relevant. In order to establish whether and how it is relevant, you would have to treat it as a variable in another set of experiments. Physical constants (e. g. the charge on an electron or the speed of light) cannot be treated as variables since so far as we know they always have the same values. constriction CONVERSE: dilation 9830 Narrowing of a vessel. Por exemplo. vasoconstriction narrowing of blood vessels, usually due to contraction of smooth muscle. contra - RELATED: anti - 9830 Against, opposite contraction CONVERSE: relaxation 9830 State of activity of a muscle in which it may produce force andor shorten, depending on the mechanical constraints on it. Note that contraction in ordinary English means getting smaller. In muscle physiology the word shortening is reserved for this, and contraction may occur even while a muscle is lengthening. Note also that activation in muscle physiology is also different from contraction, referring specifically to the electrical activation of the membrane. control RELATED: control system, control experiment 9830 Many physiological systems are control systems, maintaining homeostasis of some tissue parameters. Control here means regulation, just as you might control the temperature in your room. A control experiment, or control for short, has a different meaning. Control here means check. It doesnt take this meaning in ordinary English, unlike in some other languages (where the gasman might control your meter). A control experiment is one designed to check that a result is not due to an incidental aspect of your protocol. For example, if you dissolve a drug in oil to administer it, you should do some controls to check that oil alone does not have some effect. cooperative A process in which different individual elements do not act independently, but produce a bigger effect in combination than the sum of their effects on their own. Chemical reactions exhibiting cooperativity give a sigmoid (S-shaped) curve when product concentration is plotted against reactant concentration. correlation RELATED: regression 9830 A systematic relationship between two variables. If A tends to be high when B is high, it is a positive correlation, while if A is high when B is low it is a negative (or inverse) correlation. A correlation need not be perfect. Thus in the adult population there is a positive correlation between height and weight, even though the taller of two people is not invariably the heavier. A correlation coefficient indicates the degree of consistency of the correlation. Uncertainty and misunderstanding sometimes surround the issue whether a correlation indicates a causal relationship. If stress is correlated with early mortality, is it perhaps because stress is also correlated with smoking cortex The skin, or outer part of an organ (e. g. the cerebral cortex or adrenal cortex). coulomb The unit of electrical charge. 1 Amp 1 Coulomb flowing per second countercurrent A mechanism in which fluids flowing in opposite directions interact by transport between them of heat or solutes, etc. Such mechanisms are important in many animals for the conservation of heat in limbs exposed to extreme cold (where the transfer is purely passive), and in the kidney for the concentration of solutes in excreted fluids (where the transport of solutes involves active transport). cranial Relating to the skull (cranium). critical experiment RELATED: crucial experiment 9830 An experiment in which the outcome disproves a hypothesis, or in principle could disprove a hypothesis. It is of course true that science advances through experiments that support hypotheses. However, experiments that merely support a hypothesis and that do not disprove a different hypothesis that was otherwise plausible, are of less value: they are not critical. crucial experiment RELATED: critical experiment 9830 An experiment for which two plausible hypotheses give clearly distinct predictions. It may be better than a critical experiment, because it may separate the two hypotheses. If you think that muscle fatigue (i. e. a drop in maximum voluntary tension) might be due to either a failure of the nerve-muscle junctions or a failure in the muscle cells, then a crucial experiment would be to measure the tension due to direct muscle stimulation, before and during the fatigue. If you stimulated instead the nerve to the muscle, this would be a critical but not a crucial experiment (i. e. it could prove both hypotheses wrong, but it couldnt tell them apart). CT scan RELATED: CAT 9830 Computed tomography, or computed axial tomography. An X-ray technique in which an image of the internal structure of tissue is reconstructed, not just a shadow picture as in an ordinary X-ray. current RELATED: charge 9830 An electric current is the rate of flow of charge in a circuit. Its units are Amps (A). Moving charges may be positive (e. g. in tissue, Na . K ions) or negative (e. g. Cl - ions or (in metals) electrons). The DIRECTION of current flow is the direction that positive charges are moving, if there are any present (as there always are in an ionised solution). Negative charges move in the opposite direction. The DIRECTION of current in a resistor or in tissue is always from ve to - ve (unless the current is coupled to a chemical reaction, as in a battery, or a form of ACTIVE TRANSPORT providing energy, when charge may be moved uphill towards places with a more positive voltage. curvilinear A non-linear relation, i. e. one for which the graph is curved in at least part of its range. E. g. a sigmoid relation. data The results of an experiment or investigation. Strictly, it is the plural of datum, and you should say for example These data show. . In practice, the word datum is hardly ever used and it is probably more common to say This data shows. . database RELATED: keyword 9830 A computer program for keeping track of large numbers of related records, allowing them to be sorted, ordered, and selected on the basis of information contained in them. deca - ABBREV: da RELATED: SI units 9830 Prefix meaning ten times, as opposed to deci - meaning one tenth. Very easily confused and very seldom used in physiology. deci - ABBREV: d RELATED: SI units 9830 One tenth 10 -1. Seldom used. The SI system of units encourages units based on multiples of 10 3. A litre is 1dm 3. Old-fashioned rulers sometimes mark a decimetre (100mm). Dont talk about it decibel ABBREV: dB) 9830 A unit of intensity of sound, or other forms of energy. It is a logarithmic unit, which compresses the huge range of audible sound intensities into a range from 0-100dB or thereabouts. 10dB corresponds to an increment of 1 in the log of the sound energy, or a factor of 10 in the energy itself. The sound intensity corresponding to 0dB is nominally the threshold of hearing. This is one of the few units where the prefix deci - is used. The primary unit (1bel10dB) is seldom used at all. default What is to be understood if you dont specify something different. This word has become common through computer usage, where software will often use its own (default) values for parameters unless you take steps to change them. Some scientific words like percentage or amplitude have default meanings in particular contexts, that can nevertheless be altered. It is usually good practice not to assume a default meaning, since it may not be universally accepted. definition The precise meaning of a word or phrase. The meaning may depend on context: see e. g. control. Scientific and physiological meanings often differ from those in an ordinary dictionary. Where there is ambiguity, the context should make the meaning clear. Ambiguities are a plague in science, as in everything except the subtler arts If you are asked for a definition, give (a) one or more paraphrases of what the word or phrase can mean, (b) brief accounts of the contexts in which it might be used, with examples, (c) if appropriate, an equation relating it to other concepts (e. g. for peripheral resistance). Dont write an essay on Everything you need to know about X, except what it is. degrees of freedom ABBREV: d. f. RELATED: statistical test 9830 The number of things that can be varied independently. These may be anatomical (e. g. the shoulder has 3 d. f. of movement), or physiological (e. g. the properties of the eye mean that you have just 3d. f. in mixing colours that can be distinguished in high light levels and only 1d. f. in low light levels). In mathematics, a linear relation has 2d. f. (e. g. slope and height, or 2 points it must pass through). In statistics, the no. of d. f. is usually 1 or 2 less than the no. of variables that go into your calculation, often because the result (e. g. a standard deviation) would be unaffected if you were to use the (n-1) differences from the first sample, instead of the (n) individual measurements. delta ABBREV: 916X, 948X, dX RELATED: differential 9830 The Greek letter delta is often used to indicate a change in a parameter. dendrite A branching, tree-like structure. Most commonly, the part of a neuron that receives synaptic contacts. denominator RELATED: numerator 9830 The bottom line of a quotient. B in the expression AB. It is seldom necessary to use the word: certainly avoid it if you might confuse it with numerator. You could call it the bottom line of the expression to avoid ambiguity. dependence CONVERSE: independence 9830 Dependence of A on B means either simply that A affects B (e. g. skin temperature depends on environmental temperature) or, in some contexts, that B cannot exist without A (e. g. consciousness depends on adequate cerebral blood flow). Note that either relationship is a dependence, not a dependency (which is usually a small island off the coast somewhere - i. e. something that is dependent). dependent Dependent and independent variables are tricky concepts. In many experiments you vary something (an independent variable) and measure another (dependent) variable. When you draw a graph (e. g. say, cell volume against osmolarity of your solution), you always plot the independent variable horizontally and the dependent variable vertically. In some experiments, both variables may be strictly dependent: you might measure red cell volume and blood osmolarity in a lot of different subjects. You could plot this relation either way. You would need extra experiments, or a clear argument in discussion, to establish whether a correlation reflected a dependence of one variable on the other. depression RELATED: inhibition CONVERSE: potentiation, facilitation 9830 A decrease in the activity of tissue or the amplitude of a response. If the decrease is due to the involvement of structures (e. g. particular synapses) that appear to have the specific function of causing the depression, then it is usually called inhibition. Spreading depression is a disturbance that causes a profound but transient depression of the excitability of nerve cells in local regions of the central nervous system. Clinical depression is a mental condition characterized by extreme sadness, a component of several clinical syndromes. derivative ABBREV: dydx RELATED: partial derivative CONVERSE: integral 9830 The gradient of the graph of a function: dydx is the gradient of y plotted against x. The second derivative (d 2 ydx 2 ) is the gradient of the graph that you get if you plot dydx (the first derivative) against x. If you know the equation for a graph, you can usually write down an equation for its derivative (i. e. differentiate the equation). If you know the shape of a graph, you should always be able to sketch the graph of the derivative. In chemistry, a derivative is a compound of similar structure that can be made from another compound. derivatives (simple functions) RELATED: differentiate 9830 If you need to differentiate an equation, then you need to know the rules for differentiation, plus the derivatives of some simple functions. The most important examples are: If yx, then dydx1. If yx 2. then dydx2x. If y1x, then dydx-1x 2. NB these are really all special cases of a single rule: if yx n. then dydxnx n-1 ). If ye x. then dydxe x. If yln(x), then dydx1x. For functions of angles, the derivatives are simplest if the angles are measured in radians: if ysin(x), then ycos(x) if ycos(x), then dydx-sin(x). describe RELATED: results, discussion 9830 Describe the results is a common beginning to an exam question. You should understand how this is quite different from Discuss the results. The same distinction holds between the RESULTS and DISCUSSION in a scientific paper. Describe means give a clear account of just the facts in front of you (which may include graphs or tables). Indicate how the data were obtained, and draw attention to the amplitude and time course of any effects or correlations that are demonstrated (identifying dependent and independent variables), and try to assess which features look likely to be reproducible (either by eye or with the help of statistical tests). Try to lay a constructive base for a discussion. determine Two distinct, but straightforward, meanings: (1) To measure. (e. g. Determine the pH of the blood. means Take blood and use a pH meter. (2) To influence and control. What determines the pH of the blood asks for an account of the role of respiration and the kidney in acid-base physiology it does not invite the one line answer a pH meter. diastole RELATED: relaxation, filling CONVERSE: systole 9830 The part of the cardiac cycle during which the ventricular myocardium relaxes, pressure falls and the chamber fills with blood. Diastolic pressure is the arterial pressure at the end of diastole, i. e. the lowest arterial pressure during the cycle. differential ABBREV: 948X or dX RELATED: delta 9830 A change in a parameter. In mathematics it is a very small (actually infinitesimal) change. Gradients (rates of change, derivatives) are the ratios of differentials for two parameters plotted against each other, hence the terminology dydx. The word differential is sometimes used incorrectly for derivative. A differential diagnosis is, more straightforwardly, the process of distinguishing two clinical conditions that have similar symptoms. differential equation RELATED: boundary conditions 9830 An equation involving a derivative, or rate of change, of a function. For example, in many situations following a disturbance from a normal steady state the rate of return towards the steady state is proportional, at each instant, to the size of the disturbance: dydt-ay. This gives rise to an exponential solution: yAe - at. with a time constant 1a. A partial differential equation relates partial derivatives with respect to two or more parameters (e. g. time and position). Important examples of partial differential equations in physiology are the diffusion equation (Ficks second law) and the cable equation. differentiate RELATED: derivative CONVERSE: integrate 9830 To find the derivative of a graph, e. g. by making a sketch, by calculation with a computer, or (if you know the equation of the graph) by using the rules of differentiation. There are 3 rules: (1) If functions add, then their derivatives add: i. e. if yf(x)g(x) then dydxdfdxdgdx. (2) If two functions are multiplied, yf(x)timesg(x) then dydxftimesdgdxgtimesdfdx. (3) If y is a function of a function, i. e. yf(u) where ug(x), then dydx(dfdu)times(dgdx). Rule 3 is best understood by example: if y(1x 2 ) 3. then this can be written yu 3 where u1x 2. Therefore dydx(3u 2 )times(2x) 6x(1x 2 ) 2. These rules, plus knowledge of the simple derivatives, enable you to differentiate any function. differentiation The process of finding the derivative (gradient) of a mathematical function. The process by which cells acquire different properties during development. diffusion The process by which molecules get from one place to another (or across a membrane) by random thermal motion. Facilitated diffusion is where a special molecular mechanism in a membrane (a carrier) allows diffusion of certain molecules that would not otherwise get through: rather like a parent who lifts children over a fence. diffusion coefficient The constant that appears in either of Ficks two laws of diffusion. It has dimensions L 2 T -1. Typical values for small molecules and ions in free solution are of order 10 -9 m 2 s -1. Typical values for diffusion of gaseous molecules are roughly 10 4 times larger hence diffusion can be an important physiological mechanism in the gas phase (for example for fluxes of O 2 and CO 2 ) over much larger distances than in solution. diffusion equation The partial differential equation governing the diffusion of substances. Ficks second law of diffusion. It states that dcdtD(d 2 cdx 2 d 2 cdy 2 d 2 zdz 2 ), where c is concentration and D is the diffusion coefficient. In vector notation it is dcdtD8711 2 c. It has the same form as the equation for conduction of heat, so solutions of the diffusion equation with particular boundary conditions (see e. g. Crank: Diffusion) can often be obtained by reference to the equivalent solutions in a textbook of heat theory (Carslaw amp Jaeger: Conduction of Heat in Solids). Solutions are often gaussian or error functions. digital RELATED: binary CONVERSE: analogue 9830 A system (e. g. a computer or measuring system) that uses numbers that can only have discrete values (i. e. a limited number of specific values). A digital oscilloscope is convenient because it can store and manipulate data, but in some ways it is less satisfactory than an analogue oscilloscope, because it makes measurements at discrete time intervals and may therefore miss a signal of interest. dilatation, dilation CONVERSE: constriction 9830 Opening up of a hollow or tubular structure, such as a blood vessel or the pupil of the eye. The form dilation is apparently incorrectly formed from Latin, but seems to be rising in popularity (there is no distinction in meaning). dimension RELATED: unit 9830 The relation between the fundamental physical quantities that correspond to a parameter. Por exemplo. velocity has dimension lengthtime pressure has dimension forcearea, or mass(length x time 2 ). Quantities with particular dimensions may be measured in different units (e. g. velocity in ms or kmhr). The units must themselves have the correct dimensions however. In order to compare the size of two parameters, they must have both the same dimensions and the same units. discrete Separate, unmixed (e. g. discrete compartments in the body). Taking one of certain specific values (e. g. discrete frequencies at which a piano string will resonate: the fundamental and its harmonics). discuss RELATED: describe 9830 Read first about describe. You may be asked to discuss something specific, but in general a discussion sets out firstly what you think you can conclude from the results. This may not be anything very definite, but you should at least be able to generate some ideas (hypotheses) that could explain the data. You may also see that some ideas you might have had are ruled out by the data: this is the often the most constructive kind of conclusion in science. Put this all down. Discuss how you might distinguish the different hypotheses with extra experiments or with more information. In general, try to clarify the implications and limitations of the data, and relate it to what you already know. dissect RELATED: isolate 9830 To cut. To remove a piece of tissue or a cell from some larger structure. To separate or cut through part of a structure to expose some element of it. distal CONVERSE: proximal 9830 Far (or farther) from some implied point. The distal parts of a limb are those far from the body. Distal parts of a neuron are those far from either the central nervous system (when talking about peripheral nerves) or from the cell body of the neuron. (NB occasionally this can cause confusion: for example, the term should not be used without clarification when talking about the dorsal roots, where the two directions are opposite.) distortion RELATED: filter 9830 A change from normal, usually in relation to physical shape or the time course of a signal. A tissue may be distorted by pushing on it. A waveform may be distorted by passing it through a filter. A filter may be useful for cutting out noise or interference even if it does distort signals somewhat. distribution In mathematics, this is the way a set of points are scattered along one axis or throughout the plane of a graph. A probability distribution is the way they would be scattered if you took very many samples. It can be expressed by a histogram, showing how many points lie in each interval, or by a probability density function (essentially the same thing, for very many points and very small intervals). Data for analogue variables often has a normal or gaussian (bell-shaped) distribution, which can be characterised by a single parameter: its standard deviation. In physiology, distribution also means the range of places in a tissue where you will find a particular substance. dorsal CONVERSE: ventral 9830 Relating to the back. dose-response curve A graph of the response to an applied drug, plotted against drug concentration or dosage. double blind RELATED: blind 9830 An experimenter in which both subject and experimenter are unaware of the conditions relating to each individual subjects. For example, neither patient nor doctor may know whether the patient is taking a drug being tested or a placebo. Information about which condition relates to each subject is kept separately and used eventually at the end of the study to analyse the results. drift RELATED: trend 9830 A gradual, continuous change in a parameter. Often this is an unwanted change due to an instability in a physiological system or a gradual change in the properties of a measuring instrument (e. g. baseline drift). drive RELATED: trigger 9830 A structure is said to drive another if events in the first trigger events in the second. For example, the pacemaker region drives the cardiac cycle in other parts of the heart. Drive, as a noun, usually relates to a state of an animal in which its behaviour is directed to satisfying a particular need, such as hunger, sex, etc.. - dromic SUF Relating to direction. Por exemplo. antidromic. drug A chemical that affects biological tissues. Often the usage is restricted to chemicals that are used clinically or for research purposes, or ones that are abused socially. Nutrients, toxins, and chemicals one is particularly fond of, tend not to be called drugs. dyne The cgs unit of force: 10 -5 newtons. dys - Abnormal, painful. Por exemplo. dyspneabreathless. earth RELATED: ground (esp. in USA) 9830 An electrical concept. You cant measure a voltage at one place. You can only measure voltage differences. It is convenient therefore to have a constant reference, relative to which you measure all voltages in a circuit or a tissue. This is called earth. It is usually connected to the chassis of equipment and to the outer part (the screen) of screened cables. For safety reasons, and also to reduce interference, the reference points are usually connected to the ground and to metal parts of the building if not, the reference is said to be floating. - ectomy SUF RELATED: - tomy 9830 Cutting and removing. Por exemplo. lobectomy removing a lobe of an organ. effect RELATED: affect 9830 See affect for a clarification of the difference in meaning of these two words. efficiency The ratio of how effective something is to the maximum effectiveness it could possibly have. The thermodynamic definition is the ratio: work done by a system available free energy. por exemplo. RELATED: i. e. 9830 Distinguish carefully between e. g. and i. e.. It can give quite the wrong meaning if you muddle them. por exemplo. means example given (strictly, exempli gratia in Latin). Isto é, means that is ( id est in Latin). If you mean to say You can get drinks (e. g. beer) from the bar. and you actually say You can get drinks (i. e. beer) from the bar. then it would imply that the bar only provides beer. Einthovens triangle A standard way of analyzing the electrocardiogram, in which the electrodes are assumed for simplicity to be at the corners of an equilateral triangle. The axis of the heart is taken as the vector that would give the observed signals when projected onto the sides of this triangle. electrical axis See axis of the heart. electrocardiogram ABBREV: EKG or ECG) 9830 Voltage changes recorded with electrodes on the skin, due to the electrical events of the cardiac cycle. Standard electrodes are placed on the left (L) and right (R) arms and on the left leg or foot (L). The right leg is earthed. Additional (precordial) electrodes may be used on the front of the chest. Three standard connections of leads are usually made, to record the differences in voltages: IL-R, IIF-R, IIIF-L. Alternative augmented configurations are also sometimes used (aVR, aVL, aVR). The principal components of the EKG signal are the P wave (due to atrial depolarization), the QRS complex (ventricular depolarization) and T wave (ventricular repolarization). electroencephalogram ABBREV: EEG) 9830 Voltage changes due to the brain, recorded from electrodes on the scalp. electrolyte A salt that dissociates into ions especially when dissolved in water. An electrolyte may be strong e. g. NaCl or weak e. g. an amino acid. Any electrolyte in solution will conduct electricity. All tissue fluids contain electrolytes. Strong solutions of strong electrolytes (e. g. 3M NaCl) have a high conductivity (i. e. low resistivity). electromyogram ABBREV: EMG) 9830 Voltage changes due to muscle, recorded from electrodes on the skin over the muscle. electroneutrality The principle of electroneutrality states that the total charges on positive and negative ions in a solution must be equal and opposite. This leads to a great paradox in physiology and physical chemistry: how can this be true if at the same time we talk about fluxes of just one kind of ion (e. g. sodium ions) between the solutions on two sides of a membrane The answer is that electroneutrality is not always exact. However, unbalanced fluxes (even big enough to produce large shifts of membrane potential, say 100mV) are so small that the violation of electroneutrality would be quite unmeasurable with chemical techniques (corresponding typically to a concentration ratio of 1.0001:1). electro-oculogram ABBREV: EOG) 9830 Voltage changes due to movements of the eyes, recorded from electrodes above and below, or on either side of, the eyes. embarrass Physiologically, an organ or a function is embarrassed if it is prevented from operating normally. For example, putting your shoulder over the back of a chair can embarrass the circulation to your arm. embolism RELATED: air embolism 9830 Blockage of an artery by an embolus. Emboli in the venous circulation generally lodge in the lungs (pulmonary embolism). Arterial (systemic) emboli can be more serious, sometimes producing stroke, myocardial infarction or gangrene depending on the site of obstruction. embolus Abnormal fragments of material carried in the circulation, e. g. a blood clot (thrombus), fat, air (as a bubble) or foreign bodies. e. m.f. The potential difference between the terminals of an electrochemical cell or battery when no current is drawn from it. Units are Volts. endo - CONVERSE: epi-, exo - 9830 Within. Por exemplo. endogenous arising within a tissue. enzyme A protein that catalyses (enhances the rate of) a chemical reaction. Its action involves binding of the substrate or substrates (reactants) and a conformational change in the enzyme itself. epi - RELATED: peri - CONVERSE: endo - 9830 Above, surrounding. Por exemplo. epicardium layer of tissue immediately surrounding the heart (part of the pericardium), epidermis outer parts of the skin. epinephrine See adrenaline. equilibrium RELATED: partial pressure 9830 A condition in which there is no tendency for a substance to move spontaneously in either direction across a boundary. A solution in contact with a gas mixture will be in equilibrium when there is no net flux of gas molecules across the interface, and the partial pressures of the gases in solution are then the same as in the gas phase. An ion is at equilibrium across a membrane if there is no passive flux of the ion (though NB there might be active transport of the ion species, requiring energy, even at equilibrium. A third example is osmotic pressure: absence of passive water flux across a semi-permeable membrane (selectively allowing water across) requires that any tendency for water to diffuse (due to an osmolarity difference) is balanced by a pressure difference: this equilibrium defines the osmotic pressure difference across the membrane. equilibrium potential ABBREV: Veq(x) RELATED: Nernst equation, resting potential 9830 The value of the membrane potential of a cell at which there would be electrochemical equilibrium for a specified ion. In general in a particular cell the equilibrium potential is different for different ions. If the membrane potential is made equal to Veq for a particular ion, then there is no net passive flux of that ion even if there are open channels that are permeable to it. In nerve cell s, Veq(K) is close to the negative resting potential, while Veq(Na) is positive). The equilibrium potential can be calculated from the Nernst Equation. error bars RELATED: standard error, confidence limits 9830 Graphs are often drawn with bars at each point, as well as the mean measurement. These indicate a measure of the variability of the data that has contributed to the mean. Usually the bars extend 1 standard error above and below the mean, though it should always be stated exactly what the bars are, since they may be standard deviations or confidence limits. If they are standard error bars, then a useful rule of thumb is that if the error bars overlap for 2 sets of measurements, then the means for these measurements are certainly not significantly different. If they are separate, but not far apart, you would need to do a statistical test to see if the difference was significant error function RELATED: gaussian 9830 Error functions are integrals of the gaussian and closely related functions, i. e. the area under a part of the bell-shaped curve. You cant write down an exact expression for calculating these, but you can look them up in tables: e. g. tables of the areas under the graph of a standard normal distribution, also known as the cumulative normal distribution. eu - RELATED: ortho - 9830 Normal. Por exemplo. eupnea normal breathing. evoked An evoked response is a response following a brief applied stimulus. In neurophysiology it is often a voltage change, also called an evoked potential or an event related potential. excise RELATED: dissect 9830 To cut out and remove. excitability RELATED: threshold 9830 The ease with which a cell can be made to respond to a stimulus, for example by giving an action potential. The term is usually used loosely for comparison (e. g. low extracellular calcium concentration increases the excitability of neurons). It is not usually defined as a quantitative parameter, though it is inversely related to threshold. excitation RELATED: stimulation 9830 Stimulation above a threshold level for producing a response, particularly an action potential response of nerve or muscle cells (excitable cells). exo - RELATED: epi - CONVERSE: endo - 9830 Outside. Por exemplo. exoskeleton structural support on the outside, rather than the inside of tissue, as in many invertebrates exogenous something not normally found in the tissue. expectation RELATED: mean, average 9830 In an ordinary sense this is what you expect in a situation, given your assumptions and theories. In a mathematical sense, the expectation of a parameter is the mean value that it would have if you repeated a large number of observations (more strictly, the limit for an infinite number of observations). This can sometimes be calculated as the sum of products of all possible values of the parameter with the probability of obtaining each value. The expectation for the outcome of throwing a dice is 3.5 (16 26. 66). The expectation for the height of a subject selected at random is the mean for the population from which he is selected. experiment RELATED: critical, crucial, exploratory experiments 9830 A procedure for finding out something new or for demonstrating a known fact. In physiology, an experiment sometimes refers to a procedure carried out on a single animal or sample of tissue, sometimes to a set of procedures including control observations, etc. carried out on many animals or samples. explicit CONVERSE: explicit 9830 An equation involving a parameter (x) is explicit for x if it is written in the form x equals some expression not involving x. For example, if you have a quadratic equation: ax 2 bxc0, the quadratic formula for solution of such an equation enables you to solve the equation explicitly. exploratory experiment RELATED: critical experiment 9830 An experiment carried out to find out what happens in a particular situation, without any clearly formulated hypothesis at the start. For example, if you discovered a new type of cell in the body, but had no idea about its function, you might study the effects on it of several known hormones. Much research is of this general type. It provides information that may generate hypotheses and eventually support or disprove ideas. exponent RELATED: logarithm 9830 The power to which a number is raised: if yx a. then a is the exponent. If a1,2,3, etc. the meaning is simple: x is multiplied by itself a times. Note that x a times x b is x ab. This rule allows us to generalise to negative and fractional exponents. Firstly, x 0 must be 1, since the rule requires that x 0 times x a x a. Secondly, x - a times x a x 0 (1), so x - a is the reciprocal of x a. Third, x 1a is the ath root of x, since if you multiply it by itself a times, you get x 1. Lastly, x ba is the ath root of x b. by the same argument. You should become completely familiar with the first 2 or 3 of these rules exponential constant RELATED: time constant (964), space constant(923), rate constant, half-life 9830 This is a common way to express how fast an exponential function falls or rises. In graphical terms, if you draw a tangent to an exponential curve at any point, it crosses its baseline exactly one exponential constant to left or right. It is the reciprocal of a rate constant ( rate of change displacement from steady value . For a declining exponential, the time constant is the time it would take to reach the final steady value if the rate of decline didnt slow down. An exponential curve actually falls (or rises) to 1e (times0.368) or timese (times2.718) in this time, so an equivalent definition is the time for the value (relative to its steady value) to change to 37 or 272 of its current value (1.44 times half-life or doubling time). exponential function ABBREV: e x. exp(x) RELATED: natural logarithm 9830 The function ye x. where e is a specific number (approx. 2.718) always called just e. The exact value of e cannot (like 960) be written down. You can get as good an approximation as you like by calculating the value of (11n) n with n large enough. Try this on a calculator This definition of e (as the limit of the expression as n 8594 8734) arises naturally from the way e is introduced in the entry on the exponentia l constant. The function ex is especially important because its gradient is always exactly equal to its value. In other words, it is a solution of the differential equation dydxy. This makes it the simplest exponential relation to handle mathematically. exponential relation A relation is exponential if one parameter changes by a constant factor every time another changes by a constant amount. It has the form yatimesbx. This means that for 1 unit shift along the x axis, y gets multiplied by a constant factor b. The graph is increasing or decreasing, depending on whether bgt1 or blt1. NB, note the important difference from a power law (yatimesx b ). In an exponential relation the variable parameter x appears in the exponent. There is really only one shape of exponential curve, since all graphs of the form yatimesbx can be made equivalent by changes of scale or reversing the axes. An exponential relation gives a straight line if you plot log(y) against x, for example on log-linear graph paper. exponentials: examples Rising exponentials are seen in unrestricted population growth (e. g. bacteria, which might double their population each hour) or growth of capital in a bank account (8 interest per annum corresponds to a rate constant for increase of 0.077ann, a doubling time of 9 years, or a time constant of 13 years). Decreasing exponentials are common in physiology: disturbances often decline by an approximately constant factor per unit time, for example membrane potential disturbances with a time constant of a few ms after stimulation, or heart rate over minutes after exercise. The size of a synaptic potential declines with distance from the synapse along a dendrite approximately exponentially, with a space constant that might typically be 0.5mm. exsanguinate To let out much or all of the blood from an animal. extra - CONVERSE: intra - 9830 Outside. Por exemplo. extravasation something getting out of blood vessels. por exemplo. Example given. Por exemplo. Dont muddle this with i. e., which implies that what follows is always true, not just an example of what might be true. If you do muddle these, the reader may be led to think you have quite the wrong idea. facilitation RELATED: potentiation CONVERSE: embarrassment, inhibition 9830 A process that makes something easier or increases its effectiveness. For example, a bronchodilator can facilitate breathing. An influence is said to facilitate a response if the response to a constant stimulus is increased while the influence is applied. For example, clenching of the fists often facilitates the knee-jerk tendon reflex (the Jendrassik manoeuvre). Potentiation, on the other hand, is an increase that outlasts the influence that causes it. factor Something that influences or induces the response of a tissue. The term factor is often used when very little is known about an influence: for example, vasodilation might in some situation be caused by a neural or hormonal factor, or by a physical factor such as a change of temperature. Factor analysis is a statistical technique for identifying the combinations of known variables that are the best predictors of a measured parameter (e. g. of IQ). factorial ABBREV: n) 9830 Product of all the integers from 1 to n. 11, 22, 36, 424, etc. For large numbers, a reasonable approximation is (ne)n. farad ABBREV: F) 9830 Unit of electrical capacitance. The capacitance of a membrane is proportional to its area, and is typically about 1uF. cm -2 . faraday ABBREV: F) 9830 The amount of electrical charge per mol of univalent positive ions: 96,500 coulombsmol, i. e. about 10 5 coulombsmol. You need to know this whenever you are thinking about how much of a concentration change is associated with electrical changes, as with current flowing across cell membranes. This is the F of the quantity RTF that comes into the Nernst equation. Note that the abbreviation F is the same as for a farad. This should not lead to confusion, since a faraday is a quantity, while a farad is a unit, but you do need to be careful. fatigue A reduction in a response as a result of repeated or prolonged stimulation or activity. In the context of muscle function, it usually means a reduction in the amount of force that the muscle can produce. feedback RELATED: control 9830 Information sent to an earlier stage in a multistep process. Negative feedback has effects that reduce the subsequent feedback signal, or reduce its rate of increase. This usually has a control function, keeping a parameter in the system constant. For example, the activity of the heart raises the arterial blood pressure. If the pressure rises above a controlled level, signals are sent via baroreceptors and the brain back to the heart, leading to a decrease in heart rate. Positive feedback produces changes that lead to a further increase in the feedback signal. This can lead to runaway changes in the system, and usually to an all-or-none response (e. g. an action potential). femto - ABBREV: f RELATED: SI units 9830 One thousand million millionth. 10 -15. The smallest fraction of a unit you normally come across in physiology. For example, the small magnetic fields produced by brain activity are measured in femto-Tesla (fT). fibrillation RELATED: atrial flutter 9830 Repetitive high frequency spontaneous activation or contraction of a muscle, particularly cardiac muscle. Quivering. Atrial fibrillation is faster than atrial flutter (gt300min) and more irregular. Ventricular fibrillation is similar, and arises frequently from electrocution or a myocardial infarct: it is normally lethal within a few minutes if not arrested (e. g. by electric shock from a defibrillator) or unless blood flow is sustained by cardiac massage. filter RELATED: low, high, band pass notch filter 9830 An electrical circuit or structure that passes some things and prevents passage of others. Electrical filters usually pass and cut particular frequency components of a signal. They may be passive (not requiring a power source) or active (requiring a power source). Physiological systems, such as the kidney glomeruli, sometimes act as physical filters, passing water and some solutes to produce a filtrate or ultrafiltrate (the latter including only small molecules). A substance is freely filtered if (as with inulin in the kidney) it is in about the same concentration in the filtrate as in the filtered solution. fixation Chemical treatment of a tissue to precipitate proteins and ensure that cell structures will not change subsequently. This is the first procedure in the preparation of specimens for microscopy. Fixatives (e. g. formaldehyde, glutaraldehyde) kill cells and may introduce artefacts (distortions of normal structure). fluorescent Capable of emitting light at one wavelength when light of another wavelength is absorbed. The wavelength of the emission is always longer (more towards the red end of the spectrum) than the wavelength of the exciting light. Fluorescent dyes are useful for marking cells into which they are injected, or for labelling receptors to which they bind. Some dyes exhibit fluorescence that changes with pH or pCa, and these can be used as indicators to measure H or Ca 2 concentrations. flux RELATED: net flux 9830 Rate of movement of a substance or solute. Movement may be in both directions at once, as with molecules diffusing within solution or across a membrane, in which case the net flux is the difference between the rates in each direction separately (the unidirectional fluxes). Unidirectional fluxes are often measured with the help of radioactive tracers, labelling the solute on one side. In an equilibrium situation there is no net flux, unless active transport is involved. Flux is sometimes measured as the total amount moving per second (e. g. into a cell), sometimes as the amount moving through unit area per second. The units should make it clear which is used (e. g. mol. m -2.s -1 ). form RELATED: time course, profile 9830 The shape of a graph, for example of the time course of a parameter. The form of a relationship is considered to be independent of the scale on which the graph is drawn, on either axis. Thus the time courses for the recovery from tachycardia (high heart rate) and hyperthermia (high temperature) after exercise have the same form (both roughly exponential), even though the restoration of normal heart rate may be much faster. fractional change RELATED: proportional, percentage 9830 The fraction by which a parameter has changed, i. e. (new value - old value)(old value). Fractional changes are often multiplied by 100 to give percentage changes. frequency components RELATED: sinusoidal 9830 The waveform of any signal can be broken down into a combination of frequency components: individual sinusoidal waves, each with its own frequency. The signal is the sum of these frequency components. This is called Fourier analysis. The reason for choosing this particular breakdown of a signal is that any linear system produces a very simple response to a sinusoidal signal: an output that is sinusoidal at the same frequency, with just an amplitude and a phase to be determined. The response to an arbitrary signal can then be predicted from a simple description of its response to different frequencies. Signals may be broken down into spatial as well as temporal frequency components. frequency response RELATED: transient response 9830 The range of frequencies to which an instrument will respond. All instruments have an upper limit to their frequency response. For example, pens can follow signals up to ca. 100Hz, while oscilloscopes may follow up to 1MHz or more. The lower limit is 0Hz in a DC-coupled instrument or a higher frequency in an AC-coupled instrument. Physiological systems may also have a frequency response: e. g. the response of the human auditory system is ca. 30Hz-20kHz. Since the response of any system falls off gradually with frequency, in instrument assessment the frequency for a 3dB cut is usually specified (i. e. when the energy in the signal falls to 50, or the amplitude to 71 of normal). function In mathematics, this is merely a relationship between 2 or more variables, usually expressible as an equation. In physiology, the statement A is a function of B (where A and B are two parameters) implies not only that you could sketch a graph of A against B, but that there is a specific causal relationship: changes in B cause changes in A (NB changes in A may or may not cause changes in B). For example, urine production is a function of alcohol concentration in the blood (but not vice versa). Ventilation rate is a function of arterial CO 2 concentration, and also vice versa but note that the graphs of these two functional relations would be completely different (with opposite slopes). gain RELATED: amplifier 9830 Amplification. gate The verb to gate means to switch something on or to allow something through under controlled circumstances. A stimulator may be gated, i. e. generate pulses only when a voltage is applied at a specific (gate) input. Ion channels may be voltage-gated (i. e. open only if the membrane voltage falls within a specific range) or receptor-gated (i. e. opened or closed by the binding of a substrate to a receptor associated with the channel molecule). gaussian RELATED: normal distribution, error functions 9830 The function corresponding to the normal distribution, giving a bell-shaped curve. The equation is y a exp(-0.5x 2 ), where x is the actual deviation from the mean divided by the standard deviation. The same function arises in the mathematics of diffusion: if something spreads from an initially highly concentrated point source, the subsequent bell-shaped distributions are gaussian or closely related functions, depending on the exact geometry involved (e. g. whether it can spread in one or more directions). - genic SUF Giving rise to. Por exemplo. anxiogenic leading to anxiety. - genous SUF Arising from. Por exemplo. exogenous something that comes from outside the body or tissue. giga - ABBREV: G RELATED: SI units 9830 One thousand million. 10 9. For example, a patch electrode that is well sealed to a biological membrane may have a resistance (between the inside of the electrode to the bath solution) of several giga-ohms. glyc - Relating to glucose or glycogen. Goldman equation RELATED: Nernst equation 9830 If a membrane is only permeable to one type of ion that is present on either side, that ion will move across the membrane carrying charge, until the membrane potential adopts the Nernst equilibrium potential for that ion. If it is permeable to several ions, perhaps present in different concentrations and with different permeabilities, then the membrane potential will adopt a value intermediate between the different equilibrium potentials: a weighted average, biassed towards the values for ions with high permeability and high concentration. It is more important to understand the concepts in these terms than to remember the Goldman equation, which gives a reasonable approximation to the results. For Na, K and Cl - it can be written, with permeabilities P Na . etc. and concentrations Na i . Na o . etc. V m - RTF log e ( (P Na Na i P K K i P Cl - Cl o ) (P Na Na o P K K o P Cl - Cl i ) ) To gain some insight into the equation, see what happens to V m when any one of the 3 permeabilities becomes much bigger than all the others (as P Na does in an action potential). It should of course (and does) reduce to the appropriate Nernst Equation. graded CONVERSE: all-or-none 9830 Capable of having any one of a continuous range of values. A physiological response is graded if variations in the strength of a stimulus produce variations in the amplitude of a response: a graph of response against stimulus strength is a smooth curve, unlike the graphs for all-or-none or stepped responses. Instruments often have both graded and stepped (click-position) controls for varying their settings, for example the amplitude or frequency controls on a stimulator. gradient ABBREV: dydx RELATED: slope 9830 The ratio of changes in one parameter to changes in another. The gradient (or slope) of y plotted against x corresponds to the steepness of the graph, i. e. the amount it moves up in a small segment, divided by the amount it moves horizontally. The dimensions and units of the gradient are those of y divided by those of y. A linear relation has a constant gradient. A curvilinear relation has a varying gradient. ground RELATED: earth 9830 USA term for earth in an electric circuit. gustatory Relating to taste. g-i tract Gastrointestinal tract, from the mouth to the anus. Reduction of a reflex response on successive repetitions of a stimulus. haemostasis Blood clotting. half life ABBREV: t 12 RELATED: time constant 9830 The length of time for something (most commonly a rate of radioactive decay) to fall to 50 of its current value. If the half life is constant whatever the current value, then the decline is exponential. The half life is then ln(2) (0.69) times the exponential time constant for the decline. hardware RELATED: software 9830 The actual equipment (particularly a computer) that you use. These days, the usefulness of computer-based equipment often depends more on the quality of the software than on the hardware. The modern equivalent of A bad workman always blames his tools is perhaps A frustrated user should blame the software, not the hardware. Hebb synapse A synapse or hypothetical synapse in which strengthening of excitatory action occurs following conditions in which presynaptic firing contributes to the successful firing of the postsynaptic cell (following a hypothesis for a learning mechanism put forward by DO Hebb, 1949). hecto - ABBREV: h RELATED: SI units 9830 One hundred, 10 2. Hardly ever used. hepato - Related to the liver. hertz ABBREV: Hz) 9830 Unit of frequency. 1Hz 1 cycle or repetition per second. Por exemplo. Mains frequency is 50Hz (60Hz in the USA). A filter might pass only frequency components above 2kHz. A nerve might be stimulated at 10Hz. SI recommendations say that you should only use Hz for sinusoidal components of a signal. People seem usually to ignore this, however. Strictly according to this rule you should say you are stimulating at 10 pulses per sec, or 10s -1. unless you are using a sinusoidal stimulus current (which would be rather unusual). hetero - CONVERSE: homo - 9830 Different, varied. high pass RELATED: low pass, filter 9830 A type of filter that lets through high frequency components and removes (or cuts) low frequencies. histogram RELATED: bar graph 9830 A bar graph in which the area of each bar shows the number of observations within a particular range on the horizontal axis. The range is indicated by the bar width. This is a good way of showing the distribution of values obtained for a parameter. Values within a range (sometimes called a bin or a cell) are pooled and counted together, so that the detailed information about precise values is lost and doesnt confuse the overall picture of the distribution. homeo - RELATED: homo-, iso - 9830 Same. Por exemplo. homeostasis. homo - RELATED: homeo-, iso - CONVERSE: hetero - 9830 Same. Equivalent to homeo-, in words that come from Latin instead of Greek. Por exemplo. homogeneous (homogenous in USA) having a constant property everywhere. homogeneous RELATED: isotropic 9830 Having the same properties at every place. Distinguish carefully from isotropic. For example, the structure of contractile proteins within a skeletal muscle cell is homogeneous, but not isotropic. Any place in the cell has similar characteristics to any other, but these characteristics are very different in different directions. hormone RELATED: endocrine 9830 A chemical that is released from cells and transported to its target organ in the blood. humoral Relating to body fluids. hyper - RELATED: iso-, normo-, ortho - CONVERSE: hypo - 9830 Above normal. Por exemplo. hypertonic more concentrated than normal, tending to make cells shrink hyperventilate breathing more then normal). hyperbolic A relation for which the graph is a hyperbola, most commonly one of the form yax (i. e. an inverse proportional relation) or ya(xb)c (which is the same curve shifted on both axes, as in Hills equation for the relation between force and velocity in muscle tissue). hypo - RELATED: iso-, normo-, ortho - (all meaning roughly normal or equal CONVERSE: hyper - 9830 Below, less than normal. Used as a prefix, e. g. hypotonic less concentrated than isotonic. Hypoxic less oxygenated than normal. Hypodermic below the skin. hypothesis RELATED: null hypothesis, theory 9830 A suggestion part of a theory a postulate. Many of the explanations in physiological textbooks for how things work are really hypotheses. They may be widely accepted, or sometimes rather uncertain and controversial. It is seldom possible in science to prove that a hypothesis is correct. You should always treat scientific explanations with a healthy scepticism, regarding them as in principle capable of being proved wrong or requiring some modification in the light of new experiments. If you are asked for a hypothesis to explain some data, it is always a good idea to think of 2 hypotheses: you may then be able to devise a crucial experiment to distinguish them. i. e. RELATED: e. g. 9830 i. e. mea ns That is. (Latin: id est). This introduces either a rephrasing of what has gone before, or something that is strictly implied by it. Distinguish it carefully from e. g.. Examples: Salt can cause natriuresis (i. e. sodium excretion in the urine). Hypothermia can stop respiration, i. e. ultimately cause death. impedance RELATED: resistance, reactance 9830 Equivalent to the resistance of a circuit, but under more general conditions where the ratio of voltage and current depends on the frequency of the signals. Often it is used more or less interchangeably with resistance: e. g. you might read that the input impedance of an amplifier is 10M937. Strictly, though, impedance should be quoted for a particular frequency: e. g. gt10M937 at lt50kHz. If the impedance varies with frequency (as it will do if capacitative effects are significant) then there will be a phase difference between the voltage and the current changes. Impedance is often then expressed as a complex number (q. v.). The symbol Z is often used for impedance: ZRiX where R is the resistance and X the effective reactance in series. implicit CONVERSE: explicit 9830 An equation involving a parameter x may imply that x has a particular value, but not enable you to calculate it by direct (explicit) application of any formula. The value of x is then implicit. For example, the equation xe - x clearly has a solution (as a sketch will show), but cannot be solved explicitly. The solution (x ca. 0.675) can be found by iteration, for example by using the Newton-Rhapson method to derive the iterative formula x2(1e x ) to get a new estimate x from an existing estimate x. impulse Action potential. in parallel CONVERSE: in series 9830 Two things that happen at the same time, or are arranged side by side. The brain can often do several tasks at once, in parallel. Muscle fibres produce more force if they are arranged in parallel. in series RELATED: serial CONVERSE: in parallel 9830 Two things that happen one after the other, or that are arranged physically in a row. Resistors in series are connected end to end, giving a total resistance that is the sum of the individual values. in situ RELATED: in vivo, in vitro 9830 In the normal position in the body, or tissue. in vitro RELATED: culture CONVERSE: in vivo 9830 Literally, in glass. Often refers to a procedure carried out on cells or tissue isolated from the body and maintained in a tissue bath. inch Approximately 25.4mm. independent RELATED: dependent 9830 See dependent for a discussion of dependent and independent variables. The concepts of independent measurements and independent samples are also important. If you carry out 15 blood counts, but 5 of them were on blood from the same subject, then you do not have 15 independent measurements. The 5 are more likely to be similar to each other than to the counts from other subjects. The samples were not independent. It would be incorrect to calculate a standard deviation and to treat it as a measure of the variation of blood counts between individuals. The validity of statistical tests often depends on your samples or measurements being independent. indication A sign, hint, or suggestion. In clinical terminology: a circumstance that suggests that a particular therapeutic regime or diagnostic test is merited (as opposed to a contra-indication: a circumstance that suggests that a course of action might be unwise). indifferent An indifferent electrode is one used as a reference for measuring voltages at one or more different places, or one used when stimulating with a different electrode to pass the return current from the tissue. infarct A non-functioning, or totally dead, region of tissue (often resulting from ischaemia). infinitesimal RELATED: differential 9830 The limit of very small quantities, analogous to the reciprocal of infinity. In one sense, an infinitesimal quantity is simply zero. However, you may be interested in the ratio of two things as they become infinitesimal, when it is not helpful to think of them as zero. infinity ABBREV: 8734 RELATED: limit CONVERSE: infinitesimal 9830 The limit of very large values. Infinity is not a number, and it can be confusing to think of it as such. You can usually rephrase any statement about infinity in the form As x tends to infinity (i. e. gets larger and larger), y increases without limit, or As x tends to infinity, y tends to a particular value (i. e. gets closer and closer to this value). infra - RELATED: sub-, hypo - CONVERSE: supra - 9830 Below. Por exemplo. infra-orbital below the orbit (eye socket). infusion A continuous slow injection over a long period. Sometimes referred to colloquially as a drip, because a drip chamber is often used to check that the infusion is proceeding normally. inhibition RELATED: depression CONVERSE: excitation, facilitation 9830 An influence that reduces activity in a tissue or reduces the response produced by a stimulus. Synaptic inhibition can operate either by hyperpolarizing a cell (subtracting from the effects of excitation) or by reducing the amount of depolarization caused by excitation (diminishing the excitatory influence, with no effect unless excitation is taking place). The second situation can arise with presynaptic inhibition, and also as a result of a postsynaptic conductance increase that opens channels that tend to keep the membrane potential close to the resting potential. If the decrease of a response outlasts the influence that brings it about, it is usually called depression. innervate One tissue is innervated by another if it contains terminals of axons arising from cell bodies in the second tissue. These might be synaptic terminals or sensory terminals (as in the sensory innervation of the skin from cells in the dorsal column nuclei). The term is essentially anatomical, and does not relate to the processes of activation or synaptic transmission. input CONVERSE: output 9830 An influence or a physical route into a structure, that is capable of affecting it. The influence may be the physical entry of something (e. g. the input of food into the stomach) or the passage of information (e. g. action potentials in the innervation of the stomach). Cables connecting pieces of equipment usually have clearly defined input and output ends: signals or electric power are usually conveyed in one specific direction, which you should identify to make sense of the wiring. input impedance, input resistance The impedance (or resistance) between the input terminals of an amplifier. Amplifiers for measuring voltages without disturbing the conditions they are measuring should have a very high input impedance, so that whatever voltage the source generates, very little current is drawn by the amplifier. Input resistances of 10 12 937 are easily achieved with modern components, though at frequencies of physiological interest (e. g. 10kHz) the input impedance will be much less because the input behaves like a capacitor in parallel with a resistor. integral ABBREV: 8747 y dx) 9830 The area under a curve. A definite integral of a function f(x) is the area under the curve yf(x) between two specified values of x, in some cases plusmn infinity. An indefinite integral is itself a function of (x): the area under the curve to the left of (x). An indefinite integral includes an arbitrary constant, since the left hand limit of the area is not stated in the definition. An indefinite integral is in a sense the opposite of a derivative. If I(x)8747f(x)dx, then f(x)dI(x)dx. Thus the integrals of functions can sometimes (not always) be written down by using backwards the rules for derivatives. Integration can always be carried out numerically on a computer. inter - RELATED: intra - 9830 Between. Be careful to distinguish inter - from intra-. For example, intercellular means between cells. It may therefore refer to the extracellular space, or to junctions between cells. interpolate RELATED: extrapolate 9830 Estimate the value of a function between two or more known points, either by assuming a linear relationship between the two nearest points (linear interpolation) or by fitting a more complex function. interpreter RELATED: compiler 9830 A program that translates instructions written in a high level computer language into a form that can be executed by the computer, at the time the program is being used. The interpreter must be used every time the high level program is used (unlike a compiler). An interpreter is slow in execution compared with a compiler, because it repeats the translation process every time an instruction is used. Computers are often so fast that this is not important. Interpreters can save time if a program needs to be changed frequently, because no compiling is needed after each change. The commonest interpreted language is BASIC. interstitial RELATED: extracellular 9830 Relating to the interstices, or spaces in between things (usually cells). The interstitial space is the extracellular compartment. intra - RELATED: inter - CONVERSE: extra - 9830 Inside. Intracellular means inside cells, quite different from intercellular. invasive CONVERSE: non-invasive 9830 An invasive procedure involves putting something into the tissue under study, removing a sample of it (biopsy), or performing some surgery. Radiation, X-rays, etc. are usually regarded as invasive because the invisible penetration by particles or waves is capable of doing damage. inverse Two things are inversely related if one goes up when the other goes down. For example, pH and hydrogen ion concentration are inversely related. If the relation is not strict (as it is in this case, where there is an equation that always relates the two things exactly), then it is more usual to talk about a negative correlation than an inverse relationship. inverse function ABBREV: INV) 9830 This is in a sense the opposite of a function. If yf(x), then xINVf(y). For example, the inverse of x 2 is x 0.5 or sqrt(x), while INVlog(x)10x. Sometimes (e. g. on calculators) the shorthand terminology f -1 (x) is used, but this is potentially very confusing since it could also mean 1f(x): avoid this terminology. In trigonometry, the expressions arcsin(x), arccos(x) are used for the inverse functions of sin(x) and cos(x). The inverse of x is sometimes used to mean 1x, but this is best avoided since the word reciprocal means this and is unambiguous (e. g. conductance is the reciprocal of resistance, rather than the inverse of resistance). ipsi - RELATED: auto - CONVERSE: contra - 9830 Same, self. Ipsilateral on the same side. ischaemia RELATED: hypoxia, anoxia 9830 Cessation of blood flow. This is a normal condition in some tissues, for example in many muscles during maximal voluntary contractions. If continued for too long, the products of metabolism build up, substrates become depleted, and temporary or irreversible loss of function (infarction) may result. iso - RELATED: hypo-, hyper - 9830 Having the same value, or property. Por exemplo. isotonic, isomer isolated RELATED: in vitro 9830 A tissue separated from its normal inputs. It might be kept in the body for study (in situ) or it might be studied in vitro. An isolated stimulator is an electrical stimulator in which neither of the output terminals is connected to earth this is useful for reducing the current during a stimulus that may flow through a recording device, causing a stimulus artefact. isotropic RELATED: homogeneous 9830 Having the same properties in all directions. Distinguish carefully from homogeneous. iteration A step that is repeated many times in trying to achieve a goal (e. g. to solve an equation, or straighten a picture on a wall). If the procedure is convergent, the steps eventually make almost no further difference, and you are close to a solution. If it is divergent, the steps get further from the goal, and the procedure may be useless. For example, you can find sqrt(2) by starting with any guess (except zero) and using the iteration formula (x21x) to alter the current estimate (x) again and again. (This is an example of the widely useful Newton-Rhapson formula for iterations to solve an equation of the form f(x)0: xx-f(x)(dfdx).) i-m Intramuscular (usually referring to an injection site). i-p Intraperitoneal. An injection given into the abdominal cavity (belly). iso - equal, same, uniform isotonic RELATED: isosmolar 9830 (1) Having the same tonicity. or the same osmotic effect on cells as the fluid in their normal environment. This is not necessarily the same as having the same osmolarity (see tonicity ) because some solutes contributing to the osmolarity of a solution may be permeant and equilibrate across the membrane, and so have no effect on cell volume, or only a transient effect. (2) In muscle physiology, an isotonic contraction is one during which the tension is constant (contrast isometric ). - itis SUF Inflammation of. its and its 9830 Get these straight. One of them means it is. One is like his or hers. Which is which Dont try to rote-learn it. Think about the relationship: the apostrophe represents the missing i in it is, while in his or hers you would probably never be tempted to put an apostrophe. i-v Intravenous (an injection or infusion into a vein). joule ABBREV: J RELATED: calorie 9830 The SI unit of energy. For mechanical energy it is equivalent to a 1 Newton force moving 1 meter distance. One watt (power) is 1Js. 1J10 7 ergs (cgs unit of energy). kal - Relating to potassium (Latin Kalium, hence symbol K). Por exemplo. hypokalaemia low blood potassium. Distinguish carefully from calci-. keyword RELATED: database 9830 A word used to gain access to information in a database an index entry. kilo - ABBREV: k RELATED: SI units 9830 One thousand. 10 3. E. g. 1kg 1000g labile CONVERSE: stable 9830 Transient, short-lived, or fragile. laminar flow RELATED: vector, turbulence 9830 A pattern of flow of a fluid (e. g. blood) in which the velocity and direction of movement vary smoothly as you go from one place to another. A graph of velocity against position would be a smooth curve, usually increasing monotonically from the walls to the middle of a vessel. You can describe the flow in terms of laminae (layers) of fluid flowing steadily past each other. The physical laws governing such flow are simple (e. g. Poiseuilles Law). language RELATED: program 9830 A computer language is a set of rules for expressing instructions to a computer. Examples are BASIC, FORTRAN, PASCAL, C, Machine Language or Assembler. A low level language (e. g. the machine language for a specific computer) is one in which each instruction carries out very simple operations, and many instructions are required. A high level language includes very powerful instructions that lead to complex sets of operations. High level languages must be translated into low level instructions before they are used: this is usually carried out automatically by programs called compilers or interpreters. latency A time delay between a stimulus and the beginning of a response. Dont use the term latency when you are talking about the time to the peak of a response. The word literally means hidden time: the time after the stimulus when there is still no sign that any response is going to occur. lateral On one or other side of the body. Far (or farther) from the midline. leak In membrane physiology, a leak is a passive flux of ions by a mechanism that is either artefactual and undesired (e. g. through damaged membrane around a site of electrode penetration) or relatively unselective between different species of ions. lesion RELATED: trauma 9830 A region of injury. The verb to lesion is sometimes used for the deliberate induction of tissue damage for experimental purposes. ligand A chemical or ion that binds to another chemical. ligate RELATED: ligature 9830 To tie closed, for example, a blood vessel or duct from a gland. limit A mathematical limit is a process in which some parameter gets closer and closer to a specified value, but doesnt actually reach it. Sometimes a function is not defined actually at the value that is approached. For example, if yxsin(x), the value of y is not straightforwardly defined at x0 since both the top and bottom of the expression for y are then zero. In the limit, as x approaches zero, y nevertheless gets closer and closer to the value 1. Integration limits are the values on the x axis between which the area under a graph is calculated. line RELATED: mains 9830 USA term for mains. linear RELATED: proportional 9830 A relation between two parameters, for which the graph is a straight line. The equation relating them is of the form yabtimesx. Note that linear is not the same as proportional. A proportional relationship is always linear, since its graph is a straight line through the origin. A linear relation is not necessarily a proportional one (i. e. the line doesnt necessarily go through the origin). logarithm ABBREV: log(x) RELATED: natural logarithm 9830 Logarithms strictly are to a certain base, which should be specified. If none is specified, the base is 10, while for natural logarithms it is e. Log(x) (to base 10) is the exponent (or power) to which 10 must be raised to give the number itself. Thus if ylog(x), then x10 y. For example, log(10)1, log(100)2, log(20)1.3010, etc. Logarithm tables used to be useful because they simplified complex multiplications and divisions. With calculators and computers, you wont need them. However, logarithms are enormously useful and important in the presentation of data (see logarithmic scales) and you should know by instinct that if log(X)-6.2, then X is between 10 -7 and 10 -6 . logarithmic scale Graphs are sometimes plotted with distance along one or both axes proportional to the logarithm of a variable, rather than to the variable itself. There are two reasons. One is to separate data points that would otherwise be crammed near one axis. The other is because some relationships give a straight line plotted in this way. For example, an exponential relationship can become linear if you use a vertical log scale, while a power law becomes linear if you use two log scales. You can buy log-linear and log-log graph paper to save you having to calculate the logs. You can identify a log scale by seeing that the values change by a constant factor (e. g.times10) when you move a constant distance. lyse To break, dissolve or destroy. Often refers to cells bursting, for example, due to a hypotonic extracellular solution. macro - CONVERSE: micro - 9830 Large. Por exemplo. macrophage a large cell that engulfs particles. In computer jargon, a macro is a single command that initiates a complex set of commands. macroscopic CONVERSE: microscopic 9830 Relating to large-scale features of something magnetic resonance ABBREV: MRS, MRI RELATED: NMR 9830 Magnetic resonance. A technique for studying the internal structure and chemistry of tissue by observing its properties in a high magnetic field. MR spectroscopy (MRS) gives information about the different chemicals present. Imaging techniques (MRI) give images of the structures that differ in their chemistry, which can reveal tumours, dead tissue, etc. mains RELATED: line 9830 The domestic electricity supply. Usually 220-240V, 50Hz in Europe and 110V, 60Hz in the USA. mains hum RELATED: noise, interference 9830 A type of interference that may be picked up during electrical recording, from mains operated circuits and cables nearby. It has the frequency of the mains, and may therefore be identified by seeing whether it has a period of 20ms (16.7ms in the USA). It is usually sinusoidal, but may include higher frequency components (harmonics) giving a jagged appearance to the waveform on an oscilloscope, especially if fluorescent lights are the source of the interference. If the signal is fed to a loudspeaker, it sounds like a deep hum. malignant RELATED: cancer CONVERSE: benign 9830 A condition that gets worse if not treated. Particularly refers to a tumour that invades and destroys other tissues. maximum CONVERSE: minimum 9830 The largest value that a parameter can have (e. g. the maximum age of a particular species), or a value on a graph that is larger than values on either side (E. g. levels of growth hormone often have several maxima during the day: i. e. the graph of concentration against time has several peaks). mean RELATED: average 9830 The sum of a set of quantities, divided by how many there are. It is nonsensical to take the mean of a set of quantities that are not in the same units. For a weighted mean, each quantity is multiplied by a coefficient, or weight before summing, and the result is divided by the sum of the weights. If the weights are all equal, then the weighted mean is the same as an ordinary mean. For example, a chemicals concentration in excreted urine will be the weighted mean of the concentrations produced by each kidney, weighted in proportion to the urine flow rates produced by each kidney. mechanism RELATED: why 9830 The sequence of events, steps and interactions involved in a process. When a physiologist asks why something happens, he usually wants to know the mechanism. median RELATED: quartile, percentile 9830 The value within a distribution that is exceeded by half of the data points. The 50 percentile. medium RELATED: culture 9830 Nutrient fluid suitable for growth or maintenance of cells or tissue in vitro . mega - ABBREV: M RELATED: SI units 9830 One million. 106 or 10 6 . megaly SUF Large. Por exemplo. megalomania delusion of grandeur. membrane potential ABBREV: V m Voltage difference between the inside and outside of a membrane. V m is normally taken as the inside voltage relative to the outside, taken as the reference: V0. So V m is normally negative at rest (the resting potential). Note that some cells (e. g. in endothelia involved in transport, V m may be different on different faces, and positive on some. messenger RELATED: second messenger 9830 A chemical released in one place, that has an influence on processes in another place, e. g. a hormone, transmitter, or intracellular messenger. Its role is essentially to act as a signal, conveying information. metabolism The chemical reactions that occur in the body. Chemicals ingested or manufactured in the body are either metabolised, excreted or accumulated. metabolite A product of metabolism of nutrients or of a particular specified substance. meter SUF Measure, or measuring instrument. E. g. manometer instrument for measuring vacuum or pressure. micro - ABBREV: u (Gr mu) RELATED: SI units 9830 One millionth: 10 -6. E. g. 1000 microvolts 1mV. micron ABBREV: um) 9830 An old-fashioned word for a micrometre (1um). It used to be abbreviated as 1u, but this is confusing and strongly discouraged within SI units. The unit mu (meaning milli-micron, or 1nm) was used by spectroscopists, and is also discouraged. milli - ABBREV: m RELATED: SI units 9830 One thousandth. 10 -3. For example, the commonest unit of voltage used in physiology is the millivolt (mV). Note that the abbreviation (m) is the same as that for a metre. This does not lead to confusion if you use units correctly. If milli - is used, it always precedes a symbol for an ordinary unit, and never stands on its own. Separate units that are multiplied together should always be separated by a dot (period). Thus 1ms 1 millisecond 1m. s 1 meter second. minimal RELATED: minimum, maximal 9830 Something that is almost small enough to have no effect. Distinguish from minimum, which means the smallest value under consideration or (in mathematics) one that is smaller than its neighbours. For example: Standing up leads to a transient fall in blood pressure, but this usually has minimal effects on brain function. At its minimum, the blood pressure may have dropped by 40mm Hg. minimum CONVERSE: maximum 9830 The lowest value a parameter can have (e. g. the minimum water temperature in which a person can survive), or a value on a graph that is lower than points on either side. mks RELATED: SI, cgs 9830 System of units based on metres, kilograms amp seconds mmHg The unit of pressure most commonly used for measuring blood pressure. 1mmHg is approximately 133 Pa (pascals). The unit is retained, despite not being an SI unit, because the commonest and most accurate instrument for measuring blood pressure is a mercury sphygmomanometer, which gives a direct reading in mmHg. mode RELATED: mean 9830 The most common, or most probable value in a distribution. Seldom a useful concept in physiology, though it is often about the same as the mean or median. modulator A chemical that influences (decreases or increases) the response to another stimulus. molality RELATED: molarity 9830 A way of expressing the ratios of the amounts of substances in solution. The molality of a solute is the number of mols of solute per kg of solvent. In physiology, dealing with aqueous solutions, this is for most practical purposes almost the same as the number of mols per litre of solution (i. e. the molar concentration of the solution). Molarity is the simpler and more commonly used concept, though there are some advantages in relation to thermodynamics in expressing concentrations as molalities. Also it is useful where a significant fraction of fluid volume is non-aqueous - e. g. lipid or protein. molarity ABBREV: moll, M RELATED: concentration 9830 A common way of expressing concentrations. The unit of molarity is the moll, often abbreviated as M, or molar. A solution having a concentration of 0.2M (200mM) contains 0.2mol of solute in each litre of volume. That is the same as 0.2mmol in each ml, etc. The molar concentration is the concentration in gl divided by the molecular weight of the solute. mol, mole RELATED: molarity 9830 A unit of quantity of a substance. If the molecular weight of a substance is X, then 1mol is X grams. For example, the MW of NaCl is 48.5 (2335.5), and therefore 1mol of NaCl is 48.8g. A 1M solution would therefore contain 48.8g of NaCl in 1litre. You can usually find the molecular weight of a compound (or formula weight, e. g. for a hydrated crystalline compound such as MgSO 4 ,7H 2 O) by looking on the label, to save you going to a set of chemical tables to work it out. monotonic A relation whose gradient has the same sign at all points, at least within a specified range. Linear, exponential and sigmoid relations are all monotonic. The relation between rate of sweating and body temperature is monotonic within the physiological range. That between mental performance and body temperature is not monotonic (performance declines at both high and low temperatures). morbid Diseased. Distinguish morbidity (the extent to which something, for example an infection, causes disease) from mortality (the extent to which it causes death). motility Movement, particularly of cells or parts of cells. motor Associated with movement, or production of force, e. g. motor nerves, vasomotor tone (action potentials producing a steady contraction of blood vessels). M-current Outward K current through channels that are opened by prolonged depolarisation and closed by acetylcholine acting at muscarinic receptors. Possibly important in control of adaptation and excitability of several types of nerve cell. nano - ABBREV: n RELATED: SI units 9830 One thousand millionth. 10 -9 . natri - Relating to sodium (Latin Natrium, symbol Na). Por exemplo. Natriuretic factor something leading to extra sodium in the urine. natural logarithm ABBREV: ln(x) RELATED: exponential function 9830 Logarithm to the base e (approx. 2.718). If yln(x), then xe y. A natural logarithm is 2.303 times the ordinary logarithm of the same number: ln(x)2.303log(x). It is natural because in certain respects it is mathematically simple. For example, ln(1948) where 948 is a small fraction (ltlt1) is approximately equal to 948 (whereas log 10 (1948) 0.43 948 ). The gradient or derivative of ln(x) is 1x. Hence the integral of 1x is ln(x). negligible RELATED: minimal 9830 Capable of being neglected, not worth considering. Less than minimal. Note that negligible may only be meaningful in a clearly defined context. What can be neglected from one point of view may be important in another context. Por exemplo. a negligible alcohol consumption in relation to its effect on behaviour may not be negligible if you are trying to study alcohol metabolism. nephro - RELATED: renal 9830 Relating to kidney. Por exemplo. nephritis inflammation of kidney. Nernst equation RELATED: equilibrium potential, Goldman equation 9830 This is the equation to calculate the equilibrium potential for a particular ion, i. e. the voltage difference across a membrane that would be just big enough to counter any net flux of that ion due to a concentration gradient. If ion X (e. g. Na ) has concentrations C i and C o on the inside and outside of the membrane, and a charge z (e. g. z 1 for Na , z -1 for Cl - ), then the equilibrium potential on the inside (relative to the outside) is: V eq(X) - RT(zF) log e (C i C o ) where R is the gas constant, T the absolute temperature and F Faradays constant. At 20 o C the value of RTF is 25mV. Converting the log e to log 10 (multiplying by 2.303), the expression becomes V eq(X) -58mV z log 10 (C i C o ). At 37 o C the constant is 61mV instead of 58mV. neural network A system of neurons that are coupled together in such a way as to process information. For example, a network might produce activity in one particular neuron only when a certain class of patterns is presented (classification or feature detection), or it might generate a pattern of outputs (perhaps leading to a coordinated movement) whenever a simple input is received. The study of the behaviour of neural networks (real nervous systems, simulated nervous systems and artificial systems resembling neurons in some respects) is a large area of information science that bridges neuroscience, computer science, physics and engineering. newton SI unit of force, that which would accelerate a 1kg mass by 1ms -2. The force that gravity exerts (at sea level) on a mass of about 102g. It is reputed to be a coincidence that this is close to the mass of a 17th century Lincolnshire apple, said to have triggered an understanding of such matters. NMR RELATED: Magnetic resonance 9830 Nuclear magnetic resonance. The same as magnetic resonance. The technique is based on the physics of the nuclei within certain atoms. The word nuclear has recently tended to be dropped from the terminology in hospitals, because it is reputed to scare patients The technique has nothing to do with radioactivity, however: which is presumably what patients might be scared of. nomogram A graphical device for solving equations. A chart is prepared specially for solving a particular problem. You draw on this a straight line between points corresponding to known values, and you find the unknown value by reading where your line crosses one of the prepared lines on the chart. For example, the pH of the blood is affected, according to quite complex formulae, both by the chronic condition of a patient (reflected by metabolic acidosis or alkalosis), and by the current rate of ventilation and CO 2 levels. If you know the pH and the PCO 2 . you can use a nomogram to find the degree of metabolic acidosis directly. non-invasive CONVERSE: invasive 9830 A technique that doesnt require entry into the tissue being studied, or damage to it. Many recent medical advances have arisen through the development of non-invasive techniques that assist diagnosis (e. g. Magnetic resonance). non-parametric test A statistical test that does not require assumptions about the probability distributions of the measured parameters. It may use, for example, just the rank order of a set of data. Such tests are much used in psychology. normal RELATED: physiological, pathological 9830 1. Not a sign of disease or trauma, or a risk factor for disease. Por exemplo. A normal range of blood pressure or body weights. Definitions of normal are often arbitrary or contentious: where is the borderline of unusual behaviour and mental illness 2. A chemical unit meaning containing 1M H or OH - ions. 3. Perpendicular. normalise To divide values for some measured variable by another parameter, in order to take account of some known relationship. For example, if you wanted to see if male and female muscle can produce the same force, you might measure the forces produced by muscles in men and women. Since you know, however, that a larger muscle can produce a larger force, you would have to normalise the data with measurements of the cross-sectional area of the muscles (and perhaps the lever ratios). Otherwise you might come to the wrong conclusion because of differences in the size and geometry of muscles in men and women. normo - RELATED: eu - 9830 Normal. Por exemplo. normocapnic having normal CO 2 levels. notch filter RELATED: band pass filter 9830 An electrical filter that cuts out a narrow range of frequencies. Most commonly used to cut out mains hum (at a well defined frequency), while passing other signals of interest. noxious A stimulus that is painful or unpleasant. null hypothesis RELATED: statistical test, significance limits 9830 A hypothesis that there is no real effect underlying a difference suggested by data, and that the apparent effect is due to random variations within the data. A null hypothesis must be clear, and in some circumstances may have to be quite precise and quantitative. For example, if you know from large surveys that the mean male-female height difference between adult siblings in England is 12cm and you make a small survey in France that gives a mean difference of 15cm, your null hypothesis might be that the difference in France is really 12cm. In this way you could test whether there is a significant difference between the two populations in this respect. numerator RELATED: denominator 9830 The top line of a quotient. A in the expression AB. Avoid the word unless you are quite sure not to confuse it. numerical aperture (N. A.) RELATED: resolving power, depth of focus 9830 A quantity that describes the light gathering power and the resolving power of a lens. The N. A. is greater with a larger diameter lens, and also if the medium between the object and the lens has a high refractive index (as with an oil immersion microscope objective). This increases the resolving power (i. e. means that smaller objects can be distinguished) but reduces the depth of focus of the lens (so that objects slightly out of the focal plane are blurred). In a camera, the f-stop number (e. g. f16) is 1N. A. a small f number (e. g. f1.8) gives you lots of light, but little depth of focus. numerical methods RELATED: analytical 9830 Methods for solving mathematical problems in specific cases (with known parameters), by using calculations and approximations. Usually this requires a computer. For example, you can integrate any function numerically there are some functions that you cannot integrate analytically (e. g. exp(-x 2 )). observation A measurement, or observation of a qualitative feature. Observations of the responses to skin trauma might include changes of skin colour, swelling, changes of heart rate, vocalisation, etc. occlusion A blockage in for example, a blood vessel. The response to one stimulus is sometimes said to occlude the response to another if the response to both stimuli presented together is less than the sum of the two separately. This occurs in the nervous system, for example, where each stimulus induces an all-or-none response in some of the same neurons. oedema RELATED: edema (US) 9830 Swelling offset RELATED: shift 9830 An offset control on a recording instrument allows you to add or subtract an adjustable steady signal at the input to the instrument. This has a similar effect to a shift control (operating at the output), in that it shifts the record up or down. The amount of the shift increases in proportion to the sensitivity of the instrument, however. An offset allows you to but it shifts the record by an amount that off-scale A measurement that is beyond the range that is satisfactorily registered by a measuring instrument. This may lead to disappearance of the record (as usually on an oscilloscope) or to saturation of the record so as to give a flat recording, as on a pen recorder. In these circumstances it may be possible to use a shift or offset control to bring the recording on-scale. Alternatively, it may be convenient and satisfactory to use AC-coupling of the signal. Ohms law RELATED: resistance, conductance, current, potential difference 9830 This states that current through a material is proportional to the potential difference (or voltage) across it: IVR where R is a constant called the electrical resistance. This relation can also be written as VIR or RVI. Ohms law holds closely for most ordinary materials, like metal wires and ionic solutions (electrolytes). It doesnt hold for many special electrical components like rectifiers, or for membrane channels, or even for ordinary wires if you pass so much current through them that they get hot (e. g. light bulbs): these things have a different resistance under different conditions. olfactory Relating to smell. operator A mathematical symbol indicating an operation. Some operators are unary, i. e. act only on one number. For example, - and. indicate respectively the negative and the factorial of a number. Some are binary, acting on two numbers, e. g.,times (or ),, indicating addition, multiplication, division and exponentiation. Conventional formulae often use the relative position of numbers to indicate operations (e. g. superscripts to indicate exponentiation). Formulae cannot easily be put into a computer in this form, so conventions are adopted that use symbols all on one line (e. g. , , and instead of times to avoid confusion). Use brackets whenever there might be ambiguity without brackets: e. g. 3(2x), not 32x. order of magnitude A useful but imprecise expression. Be careful with it. 1. Used to indicate that quantities are so different in size that the difference itself rules out some hypotheses. Por exemplo. The size of a large mammal is a quite different order of magnitude from the distances over which diffusion can take place. 2. Sometimes people use order of magnitude to mean roughly a factor of ten. Por exemplo. an elephant (2000kg) is about 5 orders of magnitude heavier than a shrew (ca. 15g). 3. Mathematicians use order in a more precise way, to indicate that a ratio tends asymptotically to zero or 1 under specific conditions. ordinate ABBREV: Y axis RELATED: abscissa 9830 The vertical, or Y axis, usually used for plotting a dependent variable in an experiment. ortho - Straight, normal. Por exemplo. orthodontics straightening of teeth. - osis SUF Diseased condition involving the preceding part of the word. Por exemplo. Psychosis, tuberculosis. osmolarity ABBREV: osmoll RELATED: tonicity 9830 This is the sum of the molar concentrations of all the ions or molecules in solution. 150mM NaCl, 100mM Na 2 SO 4 and 300mM sucrose each have the same osmolarity, 300mosmoll. The osmolarity is a measure of how many particles are in solution. If two solutions are separated by a membrane that is permeable to water, water will diffuse into the solution with greater osmolarity (i. e. more particles in solution), unless there is a pressure difference to oppose this movement. output RELATED: projection CONVERSE: input 9830 A structure leading from a system or something (a chemical, signal or a form of energy) produced by the system. overshoot RELATED: undershoot, transient 9830 Part of a response to a continuing stimulus, in which the response transiently exceeds the level at which it finally settles. Note that it is not really the converse of an undershoot. paired comparison RELATED: students t test 9830 A comparison in which measurements under one condition are paired in some way with measurements under another. This is to ensure that apart from the deliberate difference in conditions, each pair of measurements has as much as possible in common. For example, the paired measurements might be made on the same subject. It isnt always possible, however, to use the same subjects twice: for example, you may be comparing different treatments for a disease. In such cases you may be able to match subjects to some extent (e. g. for similar age, sex and symptomatology). Differences between the paired measurements are calculated, and statistical tests carried out on the mean difference. para - Alongside, resembling. Por exemplo. Por exemplo. parathyroid gland beside the thyroid, paraesthesia abnormal (but not absent) sensation, paramedical alongside medicine. Can also mean a defence against something (e. g. parasol), and in chemistry two positions opposite each other on a molecule. paradigm An idealised example. The logic that defines a difficult concept, for example how one defines anaemia, alertness or clinical depression. parameter RELATED: quantity, unit, dimension 9830 The value of a quantity, including its units. partial derivative RELATED: derivative 9830 The derivative with respect to one parameter (with the others fixed), of a function that depends on two or more parameters. For example, the concentration of a chemical in solution depends in general on position and time. It has partial derivatives with respect to time (i. e. the rate of change of concentration at each place) and with respect to the three directions in space (i. e. the concentration gradients in each direction at any one time). A partial differential equation (the diffusion equation) relates these derivatives. partial pressure in a gas mixture RELATED: vapour pressure 9830 The portion of the total pressure of a gas mixture that is due to a particular constituent. The total pressure is the sum of the partial pressures, and the proportions are the same as the proportions of the quantities of gas, either by numbers of molecules or moles, or by volume (measured at a fixed pressure). For example, normal expired air contains (after drying) about 5 CO 2 by volume (5 of the molecules are CO 2 ). The CO 2 partial pressure (P CO 2 ) is therefore about 0.05 of an atmosphere (38 mmHg or 5.0 kPa). Since part of the pressure in the alveoli (about 47 mmHg or 6.3 kPa) is water vapour pressure the CO 2 partial pressure in the alveoli would be less: 0.05 of (760-47) mmHg 36 mmHg, or 0.05 of (101-6.3) kPa 4.7 kPa partial pressure in a solution RELATED: partial pressure in a gas mixture 9830 The partial pressure of a gas (like O 2 or CO 2 ) in a solution is the partial pressure in a gas mixture in equilibrium with the solution. It is not directly related to how much of the gas is in the solution. Under normal conditions, arterial blood has P O 2 100 mmHg and P CO 2 40 mmHg, close to the values in the alveolar gas mixture with which it has equilibrated. At these normal partial pressures, the amount of O 2 and CO 2 in the blood may vary depending on how many red cells and much haemoglobin the blood contains. passive RELATED: electrochemical gradient CONVERSE: active 9830 A process or event that doesnt require energy, or that doesnt require the active participation of some system. It is often wise to clarify the senses in which active and passive are being used. For example, it is perfectly correct to say that an action potential (representing neural activity) is a purely passive event, in that it involves nothing but the passive movement of ions. In the context of membrane transport, passive movement is transport down an electrochemical gradient. Passive movement of a limb is movement induced elsewhere, not by contraction of the muscles that normally act on the limb. pathogen An organism or chemical that causes disease. pathological Diseased, disordered, or abnormal. pathophysiology Study of the function of tissue under pathological conditions. pCa RELATED: pH 9830 A way of expressing very low calcium concentrations, by analogy with pH. pCa-log 10 (molar Ca concentration). Por exemplo. pCa 5 means Ca 2 10 -5 M. peak CONVERSE: trough 9830 A point on a graph that is higher than those on either side (i. e. a maximum). percentage ABBREV: RELATED: proportional 9830 A quantity expressed relative to a reference as 100. It is most commonly used to describe changes. Note carefully that a 150 increase means a final value 2.5 times the original, while an increase to 150 means a final value 1.5 times the original. Unless otherwise stated, the initial value immediately before the change is always the reference. Thus if a parameter falls by 40 and then rises by 40, its final value is 84 of the initial value, not 100. There is obviously a risk of misunderstanding in this kind of expression, so it is usually best to make it exactly clear what you mean, e. g. The parameter fell to 60 and then rose to 84 of its initial value. percentile The X percentile within a distribution is the value below which X of the data points lie. perception Awareness of something, especially a sensation due to a sensory input. There are many sensory inputs that do not lead to conscious perceptions (e. g. afferents from arterial baroreceptors and chemoreceptors). Curiously, subjects can deny any perception, or any knowledge at all of a stimulus, yet be able to identify accurately some of its properties when forced to guess what they are (e. g. in the phenomenon of blindsight in patients who have total lesions of the primary visual cortex). perfuse RELATED: superfuse, infuse 9830 To pass fluid through. Por exemplo. an isolated salivary gland might be perfused with saline. peri - RELATED: epi - 9830 Surrounding, around. Por exemplo. perineurium sheath around nerve, perinatal around the time of birth. perinatal Around the time of birth. permeability RELATED: diffusion, transport 9830 Passage of a substance by diffusion across a membrane. A membrane is said to be permeable to a substance the substance is said to be permeant. The permeability of a membrane only allows a passive net flux to take place, i. e. in the direction down the electrochemical gradient of the permeant substance. If net movement occurs in the other direction, the substance must be subject to active transport. Quantitatively, the permeability coefficient for an uncharged substance, or for an ion under conditions when the membrane potential is zero, is the flux per unit area, divided by the concentration difference between the two sides of the membrane (dimensions: LT -1 ). personal computer ABBREV: PC) 9830 A computer used by just one person, as opposed to a computer that is connected to many terminals for separate users, or a set of computers that are all connected together in a network. An IBM-compatible PC is a computer on which you can use the same software as on a common type of PC made by IBM. pH RELATED: pCa 9830 A measure of acidity. pH - log 10 (molar H concentration). Note (a) that it is a logarithmic measure, so a change of 1 unit in pH corresponds to a 10-fold change in H concentration, and 0.3 units to a 2-fold change in concentration. (b) it is an inverse measure: low pH corresponds to high H concentration and high acidity. It is easy to remember that pH7 corresponds to 10 -7 M and pH8 to 10 -8 M. Normal plasma pH, ca. 7.4, is of course in between. phage SUF Eating, engulfing. Por exemplo. phagocyte. phase RELATED: time course, amplitude 9830 1. One of the parts of the time course of an event. For example, the rising or falling phase of an action potential the recovery phase after exercise. 2. For a sinusoidal function: a parameter that indicates where you are on the waveform, relative to when the waveform crosses the axis in a positive-going direction (phase0). This is measured as an angle: 2960acutetT radians or 360timestT degrees, where t is the time relative to the crossover and T is the period. A phase shift is the amount you have to shift one sinusoidal waveform relative to another (of the same frequency) to make them have the same crossovers. photomultiplier tube An extremely sensitive light sensing device that transduces a weak light signal into an electrical signal. physiological CONVERSE: unphysiological 9830 Characteristic of the normal workings of the tissue. If an experimental condition or a type of stimulation is said to be physiological, this means that it is within the range of conditions normally experienced by the tissue within the animal. Experiments under unphysiological conditions are often enormously helpful in understanding how the tissue works. For example, study of the force produced by muscle cells when stretched farther than the skeleton will normally permit them to be stretched (i. e. beyond their physiological range) were instrumental in establishing the sliding filament theory of muscle contraction. - physis SUF Growth. Por exemplo. hypophysis outgrowth under the brain, i. e. pituitary. pi 960 3.142 (approx.) For reference: Circumference of a circle 2960acuter. Area of circle 960acuter 2. Surface of sphere 4960acuter 2. Volume of sphere(43)timespacuter 3. Volume of cone (13)960acuter 2 timesh. pico - ABBREV: p RELATED: SI units 9830 One million millionth. 10 -12 . pixel The smallest unit capable of having a range of colours or shades, in a picture made up of dots. The picture on a computer screen usually consists of at least 640x400 pixels. placebo An inactive chemical given, as a control, to a subject in an experiment. New drugs cannot be claimed to be effective unless they are better than a placebo in a controlled, preferably blind, study. Many clinical conditions show a surprising improvement in many subjects following administration of a placebo (a placebo effect). It has been suggested that the size of a placebo effect is a measure of the social and psychological skills of a doctor, since undoubtedly these play a part in therapy, and with a placebo there is nothing else to help. plasma RELATED: serum 9830 The extracellular fluid of the blood, in which the cells are suspended. If blood is prevented from clotting, the cells will settle out leaving the relatively clear, yellowish plasma. plasticity The capacity to be modified after the changes associated with development have occurred. plateau A horizontal part of a graph, where the vertical parameter ceases to be influenced along with changes in the horizontal parameter. Many dose-response curves exhibit a plateau at high drug concentrations, because the concentration is more than enough to interact fully with all the receptors practically all of the time. pool Pooled data is data analysed together, ignoring some differences in conditions, or in how it was gathered. For example, you might look at the effects of a heavy meal on exercise performance, including both male and female subjects because you thought there might be an interesting difference. If you then found no significant difference between males and females, you might pool the data from all the subjects to get the best estimate of the effects of the meal itself. post - After, behind. Por exemplo. post-ischaemic hyperaemia increase of blood flow after a cessation of blood flow. posterior Near or nearer to the back end or tail. potential difference (p. d.) RELATED: voltage, electrochemical potential 9830 You can think of this as the driving force that is tending to push electric charge from one place to another through an electric conductor. It is like a more familiar temperature difference, which makes heat flow through a thermal conductor. Potential difference is measured in volts (V). Energy is dissipated (i. e. turned into heat or work) when a charge moves between places with a p. d. 1 Joule is dissipated if 1 Coulomb moves between places with a p. d. of 1 Volt. Conversely, it takes this much energy to move a unit of charge (1 C) in the opposite direction. Thus 1 V 1 JouleCoulomb. potentiation RELATED: facilitation CONVERSE: depression 9830 An increase in the power of something a persistent increase in the amplitude of a response. The increase may last for a few milliseconds after the cause of potentiation, or for many days (for example, the potentiation of muscle strength that results from training, or the long term potentiation of synaptic strength that may be involved in memory). Facilitation, on the other hand does not outlast whatever induces it. power In mathematics: exponent. In physics and physiology, it also means rate of doing work or rate of expending energy (measured in Joules. s -1. or Watts). power law RELATED: logarithm 9830 A relationship in which one parameter is proportional to the other raised to a fixed power: yatimesx p. If you study animals of different sizes, you will find that many of their parameters scale with size according to an approximate power law. For example if x is body mass, metabolic rate and heart rate follow approximate power law relationships with p0.72 and p-0.25 respectively. (Note that the relation for heart rate is an inverse relation: heart rate is faster in a mouse than an elephant.) You can verify whether something is a power law relationship by plotting log(y) against log(x): you get a straight line with a slope of (p) if you have a power law: log(y)log(a)ptimeslog(x). prandial Relating to a meal. preparation A part of an animal, tissue, or cell, made ready for experimentation. pressure RELATED: partial pressure 9830 The degree to which a fluid pushes on boundary surfaces. It is measured as force per area, in Pascals (Pa: 1Nm -2 ). Alternative units are millimetres of mercury (mmHg: 133 Pa), standard atmospheres (760 mmHg or 101 kPa) or bar (100 kPa). Often, (e. g. when talking about arterial presure) pressure really means relative pressure - the excess above the external atmospheric pressure. Pressure differences between parts of a fluid, unless caused and balanced by gravity, cause fluid flow. The total pressure of a gas mixture (e. g. air) is the sum of partial pressures of its constituents. principal RELATED: principle 9830 Distinguish these carefully. Principal means chief - either as an adjective ( principal features ) or as a noun ( school principal ). As an aid to memory, think of a pal who is a prince and principal of a principality principle RELATED: principal 9830 Distinguish these carefully. A principle is a basic idea or mechanism. New medical principles would mean advances in medicine. New medical principals would mean a clearout of senior staff process (1) An event or set of events. (2) A long thin branch of a cell (e. g. the dendrites and axon of a neuron). profile A graph plotted against position, showing the distribution of a parameter. For example, you might plot the profile of temperature along a diameter of the arm. prognosis The predicted course of a disease or disorder. program RELATED: language 9830 A set of instructions that can be obeyed by a computer. Programs must be written in a specific language. Computers are of no value without programs. Sophisticated programs like wordprocessors or spreadsheets can allow the user to perform complex tasks by giving commands in a form that is easier to understand than a programming language. The word program in relation to computers is usually spelt in this way even in England, where the ordinary word programme (as in a programme of work) is spelt differently. prophylactic A drug or a preventative measure taken to avoid disease or infection. proportional RELATED: linear, fractional change, percentage 9830 A relationship between two parameters in which they always change together by the same factor: if you double X, you double Y, etc. They change in proportion. The equation is of the form yatimesx, for which the graph is a straight line through the origin. An inverse proportional relationship is one in which doubling X halves Y, etc. i. e. yax. The graph for this is a hyperbola. A proportional change in a parameter is the same as a fractional change, i. e. (new value - old value)(old value). proteinuria Presence of protein in urine, sometimes indicative of kidney or heart disorders. protocol The plan for an experiment. pylorus The narrow end of the stomach (pylorus) leading to the duodenum. Q 10 The coefficient often used to express the temperature dependence of chemical, biological or physical processes. It is the factor by which the rate of the process increases when there is a 10oC rise in temperature. The Q 10 is often approximately constant over a restricted temperature range, and typically may have values typically around 1.02 for diffusion in gases, 1.3 for diffusion in liquids, 2-3 for biochemical reactions and up to 20 or more for some chemical reactions. quadratic RELATED: linear 9830 A relation of the form yax 2 bxc. The last two terms are a general linear function. The first makes it curvilinear, in fact in the shape of a parabola. This is one of the simplest non-linear functions that you may use to try to get a better fit to some data than by using a straight line. quadratic formula The formula for solving a quadratic equation. If ax 2 bxc0, then x(-bplusmnsqrt(b 2 -4ac))(2a) qualitative RELATED: quantitative 9830 Relating to the nature or qualities of something, not just to the values of parameters associated with it. For example: It is uncertain whether there are qualitative, not just quantitative, differences between the brains of monkeys and those of humans. quantitative RELATED: qualitative 9830 Relating to the value of a parameter. quantity RELATED: parameter 9830 Something you can, or in principle could, measure. quartile RELATED: median 9830 A quartile is the value within a distribution, beyond which only 25 of the data lies. A distribution has upper and lower quartiles, the 25 and 75 percentiles. quotient RELATED: denominator 9830 One parameter divided by another. If the parameters have dimensions (i. e. are not simple numbers), then the dimensions and units of the quotient are those of the top line (numerator) divided by those of the bottom (the denominator). Por exemplo. peripheral resistance is the quotient of arterio-venous pressure difference and blood flow: its units are those of pressure (Pascals) divided by those of flow (mlmin), i. e. Pa. ml -1.min. q. v. quod vide (LATIN) which see: Refers you to something else you could look up, usually a definition (q. v.) in a dictionary or glossary. radian A unit of angle. 1 radian 57.3 degrees (180 deg 960). The radian is a natural unit. The distance along the curve of a circle is simply radius times angle subtended (in radians). If x is in radians, sin(x)x for small angles (within 5 for angles less than 30 degrees, or 0.5 radians). If x is in radians, the gradient of the graph ysin(x) is cos(x). rate constant RELATED: time constant 9830 If the rate of change of a quantity is proportional to its present value, then the rate constant is the proportionality constant: rate of change rate constant times value. The resulting graph of the quantity against time is exponential, with a time constant equal to the reciprocal of the rate constant. The dimensions of a rate constant are time -1. In complex dynamic systems, in which several influences may tend to cause changes in a parameter (e. g. in complex chemical reactions), each influence may be separately characterised by a rate constant the graphs of the parameters (e. g. concentrations) in such situations are not generally exponential curves. rate of change Gradient. Most often but not always refers to the gradient of something plotted against time. You might talk of the rate of change of sweat production with temperature. ratio RELATED: quotient 9830 The numerical relationship between two things, regardless of units. It is nonsense to talk about the ratio of two quantities unless they have the same dimensions. Por exemplo. The ratio of males to females in the population is 48. 52, or 1. 1.08. People sometimes give just one number for a ratio. If you do, it must be the quotient of the first thing divided by the second. It would be very confusing to say the ratio of males to females was 1.08 in the above situation. In general, a ratio expressed with one number is likely to elicit the question: Which way round reactance (capacitative) The equivalent of resistance, but for a capacitor instead of a resistor. Its units are ohms. Current will only flow in and out of a capacitor if you apply an ALTERNATING voltage to it. Therefore, its reactance is infinite for a steady voltage (i. e. if the frequency f0). The higher the frequency, the lower the reactance: X 1(2960fC) where X is the reactance (in 937), C the capacitance (in Farads) and f the frequency (in Hz). Reactance is the ratio of the peak voltage to the peak current (XVI) just like Ohms Law, though the voltage and current are 90degrees out of phase. receptor (1) A binding site, usually on a cell membrane, for a particular chemical or class of chemicals (ligands). Some functional property of the cell is usually altered depending on whether the binding site is occupied or empty (e. g. an ion channel may be opened or shut). (2) A sense organ or sensory cell: a structure that is affected by changes in the external or internal environment of an organism and that produces signals (usually action potentials) that influence other parts of the organism. reciprocal ABBREV: x -1 RELATED: inverse 9830 The reciprocal of x is the quantity that when multiplied by x gives 1. This may be a simple number, or it may be a quantity with dimensions, or a unit. For example electrical conductance is the reciprocal of resistance and is measured in reciprocal ohms (also known as mhos, siemens). recording A continuous measurement, usually plotted as a graph against time. rectifier An electrical device that has a low resistance for current in one direction and a high resistance in the other direction. Often a semiconductor diode. recurrent In the nervous system, recurrent collaterals are branches of axons that come back into a structure from which they originated. Likewise, recurrent inhibition means inhibition of a set of cells that results from activity in the cells, amounting to a form of negative feedback. Recurrent also has the ordinary meaning of something that repeats again and again. reflex A response to a stimulus in which the signals are relayed by neurons, and are not normally subject to voluntary control. reflex arc The set of structures involved in a reflex: usually afferent and efferent nerves and one or more sets of synapses. refractive index A quantity (n) that describes the ability of a transparent material to refract (bend) light. refractory period A period in which a cell or tissue is unresponsive to stimuli (absolute refractory period) or has a raised threshold (relative refractory period) following a preceding period of activity. regression RELATED: correlation 9830 The line of closest fit to a graph exhibiting a correlation. This is usually a straight line (linear regression), though sometimes a quadratic, exponential, or other curve may be fitted if the data shows a clear relationship that departs from a straight line. The criterion for closest fit is usually that the sum of the squares of the deviations of all the points from the line (either horizontally or vertically) is a minimum. If a correlation is not statistically significant, then a regression line is not, in general, of any interest and it is a bit naughty to plot it since this may suggest there is a relationship evident in the data. regulate RELATED: control 9830 To control, in the sense of keeping something constant (e. g. body core temperature) or constantly adjusted to suit current requirements (e. g. fluid excretion in the kidney). relationship RELATED: correlation 9830 Two quantities are related if a graph shows that knowledge of one enables you to predict, to some extent, the value of the other. The line of the graph must, over the range considered, be neither horizontal nor vertical. The relationship may be strict (if the graph is a definite line through all the points) or statistical (if the points are scattered, and the prediction is simply a statement about the probability distribution of the second parameter). A statistical relationship is usually called a correlation. relative humidity Water vapour pressure as a percentage of saturated water vapour pressure. In comfortable conditions about 50-70. Relative humidity increases as air is cooled, until it reaches 100 (dewpoint), when condensation occurs. relative refractory period: see refractory period renal Relating to the kidney. resistance (electrical) RELATED: Ohms law 9830 A measure of how much something (e. g. a wire or a resistor) resists the passage of electric current. The bigger the resistance, the bigger the voltage (potential difference) needed to produce a given current: RVI. Units: ohms or 937 (for V in volts and I in amps). For many objects and circuits, R is nearly or exactly constant. In other words, the current is proportional to the potential difference. This is a statement of Ohms Law. But note that Ohms Law (q. v.) does not hold for everything. resistance vessels The arterioles and small arteries, which provide the greatest resistance to blood flow of all the vessels through which the blood flows in sequence through a tissue. Consequently, the biggest drop of pressure is along the resistance vessels. resistivity RELATED: conductivity 9830 An intrinsic property of an electrical conductor. It is the resistance of a section with unit cross-sectional area and unit length. Thus the resistance along the cytoplasm of a length L of an axon with cross-sectional area A and resistivity ampro would be amproLA. Units of resistivity are 937.m. The resistivity of tissue fluids is typically 0.5-2937.m, while for copper metal it is 0.02m937.m, i. e. 10 million times less. Conductivity is 1resistivity (units 937 -1 m -1 or Siemensm). resolution 1. The degree of detail contained in a visual image (e. g. expressed by the number of pixels). 2. The acuity or resolving power of a sensory system or an instrument. 3. The termination of an acute phase of a disease, especially a stage at which inflammation disappears. resolution of measurement RELATED: accuracy 9830 Ability of a measurement to distinguish slightly different conditions. Resolution may be limited by the size of incremental steps in the measurement (e. g. a digital pH meter may give readings to 2, 3, or 4 decimal places) or by inconsistencies in behaviour. It may be possible to identify the sources of some inconsistencies and reduce them (e. g. by placing the instrument in a standard state immediately prior to a measurement). Limitations due to fluctuations that are truly random can usually be improved by a factor SQRTn by averaging n independent measurements. Resolution is just one of the factors that limits the accuracy of a measurement. resolving power (resolution) of a microscope The minimum distance between two objects at which they appear as separate objects when viewed through a microscope. respiration (1) The act of breathing. (2) metabolic reactions involving oxygen as a reactant. response RELATED: stimulus 9830 A change caused by a stimulus. retrograde Moving backwards or in an abnormal direction or (as in retrograde axonal transport) in the opposite direction to something else (the action potentials). Reynolds number ABBREV: R RELATED: turbulence 9830 A dimensionless number that characterises the transition from laminar to turbulent fluid flow in a particular geometrical situation. For flow in a straight tube, R qtimesp(960acutertimesn) where q volume flow rate, r radius, p fluid density, n viscosity. If R is greater than a critical value (ca. 1000) then the flow becomes turbulent. Transition from laminar flow to turbulence might occur because of an increase of q (in a tube with constant r) or a decrease of r under conditions with constant q. Thus turbulence in the aorta (giving a heart murmur) may occur above a critical cardiac output, or when there is narrowing (stenosis) of the aorta. - rhea SUF Flowing, running. Por exemplo. diarrheaflowing through. Ringer solution RELATED: Krebs solution, 9830 A simple saline solution that is sufficiently similar to the normal environment of a tissue that the tissue continues to behave fairly normally when immersed in it. Named after Sidney Ringer, who discovered that calcium ions are an essential component of the physiological environment of cardiac cells. Appropriate Ringer solutions vary for different tissues and different species, and according to the needs of a particular experiment. Ringer solutions are usually not bubbled with a gas mixture containing CO 2 . and therefore normally have a lower than normal bicarbonate concentration to ensure a physiological pH. risk factor Something statistically associated with an undesired occurrence, such as a disease or accident. This may be a causal factor (e. g. cigarette smoking in relation to lung cancer) or something that suggests the possible existence of a causal factor (e. g. having a relative who suffers from a genetically related disease). root CONVERSE: power 9830 The nth root of x is the number that, multiplied by itself n times, gives x. This is x raised to the power 1n. root mean square ABBREV: rms) 9830 A measure of the typical size of a quantity, regardless of whether it is positive or negative. Take all the values. Square them. Take the mean of the squares. Then take the square root of the mean: this is the rms value. The rms value has the same dimensions as the original quantity, and may therefore be measured in the same units. Por exemplo. the rms value of the mains voltage in the UK is 220-240V. The mean voltage is zero (because it is negative for half the time) and the peak values are plusmn ca. 320V. saline RELATED: Ringer solution 9830 A solution of salts, usually one suitable for bathing or injecting into tissues. The simplest saline for clinical and mammalian use is 0.9 NaCl (approx. 150mM), which is roughly isosmotic with cells. More elaborate solutions for maintaining tissues in good physiological condition are often named after scientists who worked out their formulae, e. g. Ringer, Krebs. scalar RELATED: vector 9830 A quantity that simply has a magnitude, and no direction in space. For example: concentration is a scalar, flow or flux is a vector. science citation ind ABBREV: SCI RELATED: Index medicus 9830 A reference publication in the library. Useful if you want to find published literature about a specific topic. It lists all the papers referred to (citations) in everything that is published during the year. It is particularly useful if you want to find recent work following up something published earlier: you can expect the recent work to refer to the older work, and therefore to be traceable. Available on computer operated compact disc (CD ROM). - scope SUF Instrument that allows viewing of something. selectivity RELATED: specificity 9830 Membranes and ion channels exhibit selectivity, or selective permeability: they have a higher permeability for certain substances or ions. serum RELATED: plasma 9830 The fluid that separates from blood when it clots. Approximately equivalent to the plasma without much of its dissolved proteins. shift RELATED: balance, offset 9830 A shift or position control on an amplifier allows you to add or subtract an adjustable voltage at the output of the amplifier so as to bring the recording on-scale or to a convenient height. The size of the shift is usually independent of the sensitivity of the amplifier. SI units Standard International system of units. This is based mainly on metres, kg, seconds, amps, degrees Kelvin. Larger and smaller units are named in multiples of 1000. Units larger than the standard are named kilo-, Mega-, Giga-, Tera-. Units smaller than the standard are named milli-, micro-, nano-, pico-, femto-, atto-. The prefixes deci-, centi-, deca-, hecto - are separate from the 10 3 sequence, and are used rather seldom. You should certainly know the main sequence from Mega - down to pico-, and their abbreviations: M, k, m, micro, n, p. You dont often need the other prefixes in physiology. sigmoid A curved graph that always rises as you move to the right, but for which the gradient increases at first and then decreases. If you sketched a graph of the gradient, this would rise and then fall. This is a common shape of graph in biology, for example for dose-response curves, stimulus-response curves and for chemical reactions that involve cooperative phenomena, such as the oxygen dissociation curve for haemoglobin. The word means S-shaped, but its really more like the shape of an integral sign. sign RELATED: symptom 9830 Evidence that a physician can obtain, suggesting a disorder, that is not necessarily evident to the patient. Some symptoms and signs are not related in any obvious or well understood way to the nature of the disease. signal The waveform of a parameter that varies in time. In experiments, physiological signals are often converted into voltages (electric signals) that can be conveniently processed and recorded. significance level ABBREV: P RELATED: null hypothesis, statistical test 9830 The probability that, assuming a null hypothesis, you would get by chance an effect as large as was seen in a particular experiment. This is the end result of doing a statistical test. It is usually expressed, for example, as Plt0.01, along with details of the test. Usually if Pgt0.05 a result is described as not significant (n. s.). meaning that there isnt much certainty at all that the result was not a chance one. There is no universal answer to what is an acceptable significance level. If it would challenge firm ideas to reject the null hypothesis, then you must weigh the probability that these ideas are wrong against the probability P that your results might be due to chance. sine function ABBREV: sin(x) RELATED: cosine, tangent 9830 The sine of an angle is the opposite side to that angle in a right angled triangle, divided by the hypotenuse (longest side). This can easily be generalised to negative angles and angles greater than 90deg (9602 radians) by thinking about an arm that sweeps around from the origin of a graph, making a steadily increasing angle (A) with the horizontal axis: it always intersects a circle of unit radius around the origin at a height of sin(A) and at a horizontal displacement cos(A), generating two sinusoidal functions. sink CONVERSE: source 9830 See source. sinusoidal waveform RELATED: frequency components 9830 A repetitive waveform with the equation yatimessin(wtimestp). It is often but not necessarily a function of time (t), as is described here. a is the amplitude, w the angular frequency (in radianssec), and p the phase (in radians or degrees). The signal fluctuates between a and - a, with a repeat interval (or period) of 2960w sec. The frequency (i. e. how many times the waveform repeats itself per second) is w(2960) Hz. The phase p doesnt affect the shape of the waveform, but shifts it along the time axis. Note that a cosine function, e. g. cos(wt), is simply a sinusoidal function with a phase shift: cos(wt)sin(wt9602). sketch You understand what it is to sketch an object: to illustrate its main features without necessarily producing a perfectly neat drawing with exactly straight lines and precise quantitative relationships. If you are asked to sketch a graph, much the same thing is expected. It should be clear whether lines slope up or down, which way they are curved (if at all), and where lines intersect. If quantitative information is important (e. g. you might want to indicate maximum and minimum values or normal values), mark a number against the points: dont try to plot exact axes. Try sketching the heights of people as a function of age, marking puberty and any other ages important in the context. skewed A distribution or profile that is not symmetrical about its mean. smoothing RELATED: filter, frequency components 9830 A process for removing the high frequency components of a graph. This is often useful if the original data contains a lot of random fluctuation that obscures some consistent relationship. A histogram can be smoothed by using larger bin widths. Other graphs can be smoothed by averaging adjacent points, or by taking a weighted mean of several points around each value on the horizontal axis. Smoothing leads to distortion, since sharp peaks in the graph become smaller and broader. software RELATED: database, spreadsheet, wordprocessor 9830 Computer programs. These may be highly specific to a task (e. g. for running a particular piece of equipment), or they may be very general purpose aids to doing jobs (e. g. wordprocessors). Whether it is easy to use a computer depends on the software, not on the computer. solve RELATED: explicit, implicit 9830 To solve an equation means to find the value that a parameter must have for the equation to be correct. It is always possible to write an equation involving just a single variable x in the form f(x)0. A solution is then a value of x for which the graph of yf(x) meets or crosses the x-axis. In general there may be one, or many, or no solutions depending on the shape of the graph. If there are solutions, you can always find them by plotting a graph. Sometimes it is possible to find a formula for an explicit solution. If there are several (n) unknown variables to be found, then you need at least n equations to find all the unknowns and you cannot always solve the problem graphically. soma Body. Por exemplo. cell soma cell body somato-sensory sensation on the surface of the body (touch, etc.). source CONVERSE: sink 9830 In analysing changes that occur around electrically active cells, a current source is a region where current flows out across the membranes of active cells and a sink is where it flows in. It is sometimes possible to infer the current source density from measurements of voltage change at a number of sites within the tissue. space RELATED: compartment 9830 A fluid compartment (e. g. extracellular space), or the equivalent volume that a simple fluid compartment would have to have to account for the distribution of a chemical. For example, sucrose usually remains largely in extracellular space, so the sucrose space, i. e. the amount of sucrose in the tissue divided by the sucrose concentration with which it is equilibrated, may serve as an estimate of the extracellular space fraction. space constant ABBREV: 923 (Greek lambda) RELATED: time constant, cable theory 9830 Parameters may decline exponentially with distance, as well as with time. For example, if you give a weak stimulus to a long thin cell electrically at one place, then the resulting change of voltage across the membrane falls off exponentially as you go further away (in either direction). The space constant is the normal way to measure the degree of spread: the distance for the change to fall to 36.8, exactly equivalent in other respects to a time constant. specific (1) Relating to a particular one, or a small group of things. A specific drug, inhibitor, etc. is one that performs exclusively, or almost exclusively, the function described. Specific binding of a substance in a tissue is binding to a receptor that is selective, usually with high affinity, for that substance. Specific also may relate specifically to a biological species (e. g. a specific name). (2) A parameter that characterises a property of a substance or tissue, irrespective of how much is actually present. Specific membrane resistance is the resistance of unit area of membrane (in ohm. m 2 ), and specific conductance the resistance per unit area (in mho. m -2 ). spike RELATED: impulse 9830 A brief transient deflection on a record. An action potential is often referred to as a spike, especially when recorded on a slow trace, so that details of the timecourse of the individual action potentials are not apparent. spreadsheet RELATED: database, wordprocessor 9830 A general purpose computer program to help with calculations and (usually) drawing graphs. A quite revolutionary tool for scientists (and for business), which enables you to do elaborate calculations and to lay the results out clearly, without learning to write programs. standard 1. Something having a parameter with a known fixed value, used for calibration purposes, e. g. a standard battery (with a known voltage) or a standard solution with known concentration. 2. A way of assessing something according to an agreed rule, e. g. a standard deviation. standard deviation ABBREV: s. d. RELATED: variance, standard error 9830 This is the commonest measure of the variability of a quantity. It is the square root of the variance, and is usually more convenient than the variance because it has the same dimensions as the quantity itself (and therefore can be measured in the same units). For example, if you measured urine production in 20 of your colleagues, you might express the results in the form 230 plusmn 35 mlhr (mean plusmn s. d. n20). Generally about 70 of the values will fall within plusmn 1 s. d. of the mean (i. e. in this case, between 195 and 265 mlhr). standard error of mean ABBREV: s. e.m. RELATED: standard deviation, error bars 9830 An estimate of how much in error the mean of a set of measurements is likely to be, compared with the true mean you would get with very many measurements. It is the estimated standard deviation of the mean. With a small number (n) of measurements, the s. e.m. is larger. It is equal to the estimated standard deviation of the measurements (which tells how variable they themselves are) divided by sqrt(n). When you do an experiment, you may not be particularly interested in the variability of the original data (i. e. in the s. d.), but if you calculate a mean you should always be interested in how uncertain that is (i. e. in the s. e.m.). Calculators or spreadsheets do most of the work for you. stasis Constancy cessation of movement. Por exemplo. homeostasis, haemostasis. statistical test RELATED: null hypothesis, significance level 9830 A procedure to estimate the probability that an observed experimental result (or one even stronger) might have been obtained by chance, on the assumption of a null hypothesis. A test may in general be one-tailed or two-tailed. A one-tailed test gives the probability that the result would be as large or larger in the observed direction. A two-tailed test gives the probability (often just twice as great) that it be as large in either direction. If you predicted the effect in advance, and that is how the experiment turned out, then a 1-tailed test is appropriate. In other circumstances, a 2-tailed test should be used. std. dev. of functions If a quantity (y) is calculated from parameters x 1,x 2,etc. then it may be possible to calculate the standard deviation (sd) of y from the sds of the other parameters. With only one parameter (i. e. yf(x)), then sd(y)sd(x)timesdfdx, where dfdx is the absolute value of the gradient of y plotted against x. If yatimesx p (a power law), then the sd expressed as a percentage (sd) is simple: sd(y)ptimessd(x). For example, a 3 sd in the diameters of spheres corresponds to a 9 sd in their volumes. With 2 or more parameters, with statistically independent variations, the variance V(y)931 i (V(x i )(dfdx i ) 2 ). These formulae are not always exact, but are good approximations for small variations. std. dev. of sums amp products Two special cases of the calculation of the standard deviation (sd) of functions are common and important. If a quantity y is calculated from variable parameters x 1,x 2 . whose variations are statistically independent, then simple rules apply. If y is the sum or difference of x 1,x 2 . then the square of sd(y) is the sum of the squares of the sds for all the x i . If y is the product or quotient of x 1,x 2 . then a similar rule applies but in relation to the sds expressed as percentages (sd): the square of sd(y) is (approximately) the sum of the squares of sd for all the x i . regardless of whether they appear on the top or the bottom of the formula for y. steady state RELATED: equilibrium 9830 A state in which all parameters are constant (i. e. not changing with time). In biological experiments, this is really a matter of all important parameters being considered constant. For example, there may be continuing fluctuations of concentration or voltage within the tissue. Age is a relevant parameter in many experiments and is never strictly constant If you place a cell in a new solution, its resting membrane potential may rapidly (within seconds) reach a new steady state, but the concentrations of chemicals in its cytoplasm may change slowly and take hours to reach a new steady state. You need to use the concept with care. stimulus RELATED: response 9830 Strictly urging on, this means something that activates a tissue or process. Por exemplo. arterial CO 2 is a stimulus to respiration. Any external intervention applied to a tissue is described as a stimulus, however, even if the effect is inhibition or depression of function. This can be confusing: a stimulus can stimulate (i. e. activate) or inhibit some function. The usage is sensible in as much as interventions act by inducing some change in the tissue, which may itself either activate or inhibit particular processes. The effect of one tissue on another (e. g. nerve on muscle) is not stimulation unless it its effect is excitatory. The vagus certainly does not stimulate the heart. stomy SUF RELATED: - tomy 9830 Mouth. Por exemplo. tracheostomy making an artificial opening (mouth) in the trachea (windpipe). Distinguish from - tomy (e. g. tracheotomy). Students t test RELATED: Null hypothesis, significance level 9830 A very useful statistical test in which you compare the mean value of an observation with the value that you might expect according to a null hypothesis. t is the difference from the expected value, divided by the standard error. You need to know the number of degrees of freedom ( the number of observations, less 1) and you can then look up the minimum value of t for the required significance level in a set of tables. As a rule of thumb, the difference is never significant if tlt2, while tgt2.5 will always be significant (Plt0.05) unless you have very few observations (lt6). A more complex t test is required if you want to compare 2 means. sub - RELATED: hypo-, oligo - CONVERSE: super - 9830 Under, beneath. Por exemplo. subnormal, sub-lingual (under the tongue). subject Human experimental animal. A patient participating in an experiment or a clinical trial is a subject a normal subject participating in an experiment, even in a hospital, will not appreciate being called a patient summation ABBREV: 931 (Greek Sigma) 9830 1. Mathematically, this means to add a set of numbers: Sigma(x) means the sum of all the numbers like x. For example, in calculating a line of closest fit (a regression) you choose the parameters in a function f(x) so as to minimise Sigma((y-f(x)) 2 ). 2. Physiologically, summation means the addition of influences that arrive at a cell either at separate times (temporal summation) or at separate places (spatial summation). super - RELATED: supra-, hyper - CONVERSE: sub - 9830 Above. superfuse RELATED: perfuse, infuse 9830 To pass fluid over something. Por exemplo. the tongue might be superfused with solutions containing chemicals with different tastes. supra - RELATED: super-, hyper - CONVERSE: sub - 9830 Above. supramaximal RELATED: maximal, threshold 9830 Above maximal. A supramaximal stimulus is more than big enough to have the full effect: increasing it further will not increase the response. The stimulus is therefore on the plateau of a stimulus - response graph. This may be because the stimulus is above the threshold for all of the cells contributing to a response. suture A stitch made with needle and thread or a metal clamp, to hold tissue together. sweep The left to right movement of the spot on an oscilloscope. symptom RELATED: sign 9830 A change noticed by a patient, that indicates an underlying disorder. A presenting symptom is one that leads the patient to seek medical advice: it is not necessarily indicative of the most serious aspects of the disorder. syncytium A set of cells that are coupled in some way, so that they behave in certain respects as if their cytoplasm was continuous. For example, electric current can pass through the gap junctions between cells in the heart, allowing an action potential to propagate throughout the heart without synaptic transmission. syndrome A set of symptoms andor signs that are characteristic of a particular disorder. systole RELATED: diastole 9830 The time of contraction of the ventricles of the heart, when arterial blood is expelled into the aorta. Systolic pressure is the maximum arterial pressure reaches during the cycle, at the end of systole. tangent RELATED: gradient, slope 9830 A straight line that meets a curve and also has the same gradient at the point of contact. teleological Relating to the purpose of a tissue or organ. A teleological argument whereby, for example, you say I know what this hormone is for, so it must have this effect because that is how it would easily achieve its purpose is sometimes useful in helping to remember facts or guess at them. But it isnt very reliable, since biological evolution may not always have led to the same principles of successful design that you think would be sensible temporal 1. Relating to time. 2. Relating to the temple, or side of the head. tera - ABBREV: T RELATED: SI units 9830 One million million, 10 12 . tetanus RELATED: twitch 9830 In muscle physiology, a continuous contraction produced by stimuli or action potentials at a high frequency. A fused tetanus is one in which the frequency is high enough that responses to individual stimuli cannot be distinguished. Tetanus (or lockjaw) is also a disease in which sustained muscular contractions occur. The word is used in neurophysiology to denote high frequency stimulation, though this is often considered improper since the origin of the word has to do with the tautness of muscle, not with the frequency of stimulation. - thermic SUF Relating to temperature. threshold RELATED: excitability 9830 Minimum strength of stimulus that elicits a response. time constant ABBREV: 964 (Greek tau) RELATED: exponential constant, half life, rate constant 9830 The exponential constant for a parameter that varies exponentially as a function of time. The equation for the parameter is of the form ya. e t964 or ya. e - t964. depending on whether the exponential is rising or falling. In either case, a is the value at time t0. One time constant 1.443 half lives. The reciprocal of 964 is the rate constant. Por exemplo. the time constant for cooling of a cadaver is (according to Agatha Christie) 3.5 hrs. You should be able to sketch the cooling graph and mark the time constant on it by eye. time course RELATED: latency, rise time, overshoot, undershoot 9830 The temporal (i. e. time-related) characteristics of a response or event. In general, if you are asked to describe the time course of a response you should consider whether there is a latency, what the rise time or the time to peak is, whether the response is transient or maintained, whether there is an overshoot or undershoot, how long the recovery takes, and whether the effect of the stimulus is reversible. Not all these factors may be relevant, and there may be others (e. g. perhaps several peaks in a response). You dont need to make precise measurements, but you should make approximate quantitative statements. Try describing, from experience, the time course of effects of running a mile. timebase RELATED: trigger 9830 The part of an oscilloscope that moves the spot steadily from left to right. It always has a control for varying the speed of movement (the sweep speed) and various controls for determining when the sweep begins (trigger controls). The trigger options are usually FREE RUN, i. e. it starts to sweep as soon as the last sweep is complete, EXT TRIG, i. e. it starts when a pulse is fed through a cable into a socket on the front of the timebase, INT TRIG, i. e. it starts when the vertical deflection on one of the traces exceeds an adjustable level, LINE, i. e. it starts at a constant phase of the mains voltage supply - tomy RELATED: - ectomy 9830 Cutting. Por exemplo. lobotomy incising a lobe of an organ. tonic CONVERSE: phasic 9830 Continuous. A tonic response is one that is maintained during the period of a stimulus, i. e. that does not show complete adaptation. Muscle tone is a continuous level of contraction, arising usually from tonic activity in the innervating nerves (e. g. in skeletal muscles and vascular smooth muscles). tonicity RELATED: osmolarity 9830 In physical chemistry, this is the same as osmolarity. In physiology, it relates specifically to the behaviour of cells in a solution. It is a measure of the tendency of a solution to make cells swell or shrink. An isotonic solution leaves cells at normal volume. A hypotonic solution (e. g. a more dilute solution, with lower osmolarity) makes cells swell a hypertonic solution makes them shrink. Substances in solution that readily pass through membranes (e. g. urea) contribute to the osmolarity of a solution, but not to its tonicity. A 1M urea solution has a higher osmolarity than blood plasma, but is hypotonic. Water will enter the cells along with the urea, and make the cells burst. toxin A poisonous or harmful substance. Many useful drugs have toxic effects. transducer RELATED: transduction 9830 Something that converts a signal (in more rigorous terms: energy or information) into a different form. For example, the conversion of a light signal into an electrical signal by a photomultiplier tube. Sensory receptors are transducers, though the term is more usually applied to instruments. trace A record from a measuring instrument, in graphical form. transient RELATED: phasic CONVERSE: maintained 9830 Not maintained. Por exemplo. Cigarette smoking gives a transient feeling of well-being and contributes to a long term health risk. transmitter RELATED: modulators 9830 A chemical messenger released at a synapse by the pre-synaptic cell, and acting on receptors in the postsynaptic membrane. Transmitters have a rapid local action, most often acting by opening channels in the postsynaptic membrane. The same chemicals may also be released as hormones (e. g. noradrenaline) or as modulators. transport In the context of membrane physiology, (verb) to move across a membrane. trauma RELATED: lesion 9830 A painful, harmful, or destructive event, or the wound caused by such an event. The word is used in relation to both physical and psychological damage. trend RELATED: regression, correlation 9830 1. An approximate relation, or a generalisation that is true on average but not in every individual case (as in a correlation). Por exemplo. There is a trend for taller people to be heavier. There is a trend towards lower calorie food intake in the summer. 2. Some people use trend to mean a difference found in an experiment, that doesnt reach statistical significance. Usually it is a waste of time to talk about such differences. Certainly it is dangerous to suggest, by giving them a special name, that they are worth paying attention to. The whole idea of a statistical test is to show whether a difference is too small to be worth paying attention to. trigger RELATED: all-or-none 9830 Something that starts something else off. Por exemplo. An action potential may be said to be triggered by a stimulus that is above threshold a fit of coughing may be triggered by a deep breath the start of the sweep of an oscilloscope may be triggered by a brief pulse coming from a stimulator circuit. The essential thing here is that the triggering event doesnt merely affect what is triggered, but it causes the start of a stereotyped chain of events. The relation between the trigger and the triggered event is usually all-or-none. The analogy with the trigger of a gun is fairly obvious. trophic Relating to nutrition or growth. A trophic influence is one that influences growth or maintenance of a tissue. tropic SUF Related to direction. Turning. Por exemplo. trophotropic turning or moving towards food. trough CONVERSE: peak 9830 A point on a graph that is lower than those on either side (i. e. a minimum). turbid Muddy, milky (e. g. a suspension of cells). turbulence RELATED: laminar flow, Reynolds number 9830 A state in which fluid flow fluctuates markedly from one place to another and from one time to another. The pattern of flow is then governed by the physics of chaos (which is not yet well understood) rather than the physics of laminar flow. Transition from laminar flow to turbulence often occurs quite suddenly as the rate of flow is increased or as a constriction is narrowed (e. g. in a cardiac valve). The transition can sometimes be characterised by a Reynolds number. You can picture it as the transition from dark to white water in the flow of a river. Energy is dissipated in additional ways (e. g. by sound), and different stresses are placed on the walls of a vessel. turgid Swollen, rigid (e. g. a cell in a hypotonic solution). twitch RELATED: tetanus 9830 The response of a muscle cell to a single action potential. undershoot RELATED: overshoot 9830 A phase of the time course of a response in which the measured parameter may cross below the baseline level and be shifted in the opposite direction from the initial response, before final recovery. For example, if you hyperventilate deliberately, your respiration rate will normally show an undershoot subsequently. Terminology is rather ambiguous (and should be explained more clearly) if you are discussing a response in which the initial effect is a decrease. For example if you deliberately hypoventilate (or hold your breath), the subsequent hyperventilation is best not described as either an undershoot or an overshoot. uniform RELATED: homogeneous 9830 Having the same value, usually in different places or between different subjects (not necessarily at different times). Por exemplo. Oedema due to over-drinking is relatively uniform throughout all tissue compartments. If you do experiments on students, you usually have a population with very uniform ages. unilateral RELATED: ipsi-, contralateral CONVERSE: bilateral 9830 On one side only. unit RELATED: dimension 9830 The standard to which a quantity is compared, in assigning it a numerical value. It is useless to give numerical values to parameters without specifying the units, and dangerous to compare values without converting them to the same units (NB if you insist on doing this, you have to bear in mind the relation between the units as well as the relation between the two values - unnecessary mental gymnastics). Por exemplo. metre (m) or millimetre (mm) for length pascal (Pa Nm -2 ) or mm Hg (ca. 133 Pa) for pressure. upregulation Increase in something (usually the expression of a signal or a receptor), in response to a stimulus. - uresis Relating to, or appearing in, the urine. Por exemplo. diuresis extra urine, proteinuresis protein in the urine. valid Sound, logical. Note that an argument may be invalid, even if the conclusion is correct. (The patient may have cancer even though your reasons for thinking this were invalid.) vapour pressure RELATED: relative humidity 9830 The partial pressure of a vapour (evaporated liquid) within a gas mixture. When in equilibrium with a liquid at a particular temperature, the gas has a vapour pressure equal to the saturated vapour pressure. For water, this is 6.3kPa (47mmHg) at 37 o C and 2.3kPa (18mmHg) at 20 o C. variable RELATED: parameter, constant, dependent CONVERSE: constant 9830 A parameter that you can alter or expect to vary during an experiment. For example, during an experiment on a human subject, the inspired oxygen concentration and body core temperature may be variables, but body height is a constant parameter. In experiments on several subjects, height becomes a variable, that may or may not affect the results. Variables can be dependent or independent. If you look at how body temperature is affected by exercise, temperature is a dependent variable. If you vary body temperature directly (e. g. in a hot or cold bath) and look at its effect on mental capacity, temperature is the independent variable. variance RELATED: standard deviation 9830 A measure of how variable a set of numbers is. You first have to think about the individual differences of all the numbers from the mean value for all of them. These differences will be both ve and - ve, with a mean of zero. If you square them before taking the mean (making them all positive), then you get the variance. In other words, it is the mean square difference from the mean, or strictly the limit that this would approach if you take more and more samples. The standard deviation is the square root of the variance. vaso - Relating to a vessel (i. e. in anatomy, a tube). Usually relating to a blood vessel (e. g. vasoactive affecting blood vessels), but NB vasectomy removal of a part of the vas deferens. vector RELATED: scalar 9830 A quantity that has direction as well as magnitude. You can represent it visually as an arrow. For example, the velocity of blood flow is a vector, having magnitude and direction everywhere within a blood vessel. If the flow is laminar in a straight vessel, the direction is everywhere the same, but the magnitude falls off towards the vessel walls. At a branch point, the vectors in different places have different directions. If there is turbulent flow, the vectors fluctuate somewhat chaotically with both position and time. You can resolve a vector into components in 3 perpendicular directions. NB vectors with zero magnitude do not have a defined direction. vector differentiation ABBREV: grad, div, curl) 9830 3 types of vector differentiation are defined. The first is differentiation of something (such as concentration C) that isnt itself a vector. You can take the derivative of this with respect to position in each direction and form a vector from the 3 components: this is grad(C) (vC), proportional to the flux of substance that will diffuse in the concentration gradient. If a vector A is defined at every point (e. g. flux or velocity of movement) then the divergence div(A) (v. A) corresponds to the rate at which moving particles are being added locally to the system. (NB often v. A0.) Curl(A) (vxA) is a vector corresponding to the circulation (like a vortex) of particles locally. vector multiplication ABBREV: A. B, AxB) 9830 Two types of vector multiplication are defined. Both are generalisations of the ordinary multiplication of simple numbers. A scalar product A. B is the magnitude of vector A times the component of vector B in the direction of A. It arises, for example, if A is a force applied to a point and B is its displacement: A. B is then the work done during the movement (NB work is a scalar: it doesnt have direction). The vector product AxB is twice the area formed by the triangle defined by A and B. This has direction (perpendicular to the plane of the triangle) as well as magnitude, i. e. it is a vector. It arises, for example, in calculating the force due to a current (A) in a magnetic field (B). vectorcardiography A way of analyzing electrocardiogram signals in which the signals are displayed as a spot moving in two or three dimensions, corresponding to the changes of both amplitude and electrical axis of the electrocardiogram during the cycle. The spot traverses loops, which give a direct visual indication of the electrical axis. ventilate RELATED: breathe 9830 To cause air to flow through the airways. vivisection Literally, means to cut something living. Refers to experiments on living (including anaesthetised) animals. Anti-vivisectionists are those who oppose the use of animals for experiments. Opposition to animal experiments should be distinguished from opposition to cruelty to animals. Most people who perform animal experiments for biomedical and veterinary research are wholly opposed to cruelty and would argue strongly that their work causes little or no suffering to animals, and that where suffering is caused (as is inevitable, for example, in some research on pain) it is more than balanced by the alleviation of suffering due to the successes of such research in leading to clinical advances. voltage see potential difference waveform RELATED: time course, profile 9830 The shape of the graph of a signal plotted against time, showing its timecourse. wavelength The distance between two points of equal phase on a (sinusoidal) waveform, for example between wave crests. For a light wave, wavelength is inversely related to frequency. In the visible spectrum the shortest wavelengths (ca. 0.4nm) correspond to violet light and the longest (ca. 0.8nm) correspond to red light. white noise RELATED: hum 9830 A signal that fluctuates randomly in time, with a large range of different frequency components. If you played it through a loudspeaker it would sound like a hiss. All amplifiers generate a certain amount of such noise. The term white comes by analogy with white light, which usually contains all different frequencies (or wavelengths) of light. The energy in white noise is proportional to the bandwidth. You can learn to distinguish white noise on an oscilloscope from, for example, sinusoidal hum due to signals picked up from the mains (50Hz). why A why question in physiology may relate either to the mechanism by which something happens (As a result of what processes) or to the role that it plays in affecting other things, i. e. its consequences (For what benefit). A full answer (e. g. to the question Why does peripheral resistance rise when a person stands up) would include both aspects: in this case the reflex mechanisms, and also the consequences if these did not exist. Try to avoid the ambiguity if possible, and if in doubt (e. g. in an exam) say how you are interpreting the question. wordprocessor RELATED: spreadsheet, database 9830 A computer program used to help in the preparation and editing of text documents. 967 2 RELATED: students t test, significance 9830 Chi squared test. Often used for testing the significance of the differences of two proportions. For example, if 70100 patients given a new drug recover, while only 2050 given a placebo recover, is there significant evidence that the drug has an effect
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