| electrical coupling | <physiology> General term for an intimate cytoplasmic contact, mediated by gap junctions, between touching cells, such that electrical current injected into either cell changes the membrane potential of both. In neurons, arrays of gap junctions form electrical synapses, that allow action potentials to pass directly between cells. However, electrical coupling is not confined to excitable cells: many embryonic and adult epithelia are coupled, possibly to allow metabolic cooperation. (18 Nov 1997) |
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| electromagnetic coupling | <physics> A means of extracting energy from a magnetically confined plasma, where the plasma expands and pushes on the confining magnetic field, causing electrical energy to be generated in the external field-generating circuits. (09 Oct 1997) |
| energy coupling | <chemistry> The tranfer of energy produced in one reaction to another. (09 Oct 1997) |
| excitation contraction coupling | <physiology> Name given to the chain of processes coupling excitation of a muscle by the arrival of a nervous impulse at the motor end plate to the contraction of the filaments of the sarcomere. The crucial link is the release of calcium from the sarcoplasmic reticulum and the analogy is often drawn between this and stimulus secretion coupling, that also involves calcium release into the cytoplasm. (18 Nov 1997) |
| fixed coupling | Where several premature beats are seen, the interval between each of them and the preceding normal beat is constant. Synonym: constant coupling. Variable coupling, where several extrasystoles are seen, the interval between each of them and the preceding sinus beat varies. (05 Mar 2000) |
| adaptor hypothesis | A hypothesis, proposed by F.H.C. Crick, that an adaptor molecule must be present between the information-containing DNA and the protein being synthesised. (05 Mar 2000) |
| altered self hypothesis | The hypothesis that the T-cell receptor in MHC mediated phenomena recognises a syngeneic MHC Class I or Class II molecule after modification by a virus or certain chemicals. See: MHC restriction. (18 Nov 1997) |
| alternative hypothesis | In Neyman-Pearson testing of a hypothesis, the hypothesis or family of hypotheses about the numerical value of a parameter if and only if the null hypothesis is rejected as untenable. (05 Mar 2000) |
| autocrine hypothesis | That tumour cells containing viral oncogenes may have encoded a growth factor, normally produced by other cell types, and thereby produce the factor autonomously, leading to uncontrolled proliferation. (05 Mar 2000) |
| Avogadro's hypothesis | <physics> The hypothesis that equal volumes of two different gases at the same temperature and pressure contain the same number of molecules. (02 Jan 1998) |
| Bayesian hypothesis | An array of surmised values of a parameter to be severally explored in the light of a current set of data, with logical symmetry being preserved among all. The merits of each hypothesis entertained are based on quantity, the prior probability. The probability of the data conditional on the hypothesis is computed as the conditional probability for each; the product of the two for each hypothesis is the joint probability, and the ratio of each joint probability to the sum of all the joint probabilities is the posterior probability for that hypothesis. Unlike the Neyman-Pearson test of hypotheses, the answer is a statement about the hypothesis, not about the sample conditional on the hypothesis. No hypothesis is preferred or prevails by default. The procedure may be applied recursively any number of times, as the data becomes available. (05 Mar 2000) |
| Makeham's hypothesis | A development of Gompertz' hypothesis as to the force of mortality following some mathematical law. Makeham assumed that death was the consequence of two generally coexisting causes: 1) chance; 2) a deterioration or increased inability to withstand destruction. The first of these is constant, the second is an increasing geometrical progression. (05 Mar 2000) |
| gate-control hypothesis | A theory to explain the mechanism of pain; small fibre afferent stimuli, particularly pain, entering the substantia gelatinosa can be modulated by large fibre afferent stimuli and descending spinal pathways so that their transmission to ascending spinal pathways is blocked (gated). Synonym: gate-control hypothesis. (05 Mar 2000) |
| Gompertz' hypothesis | A theory that the force of mortality increases in geometrical progression, being based on the assumption that the average exhaustion of a person's power to avoid death is such that at the end of equal infinitely small intervals of time he loses equal proportions of the power to oppose destruction which he had at the commencement of each of these intervals. (05 Mar 2000) |
| Michaelis-Menten hypothesis | <chemistry> That a complex is formed between an enzyme and its substrate (the O'Sullivan-Tompson hypothesis), which complex then decomposes to yield free enzyme and the reaction products (Brown hypothesis), the latter rate determining the overall rate of substrate-product conversion. See: Michaelis-Menten constant, Michaelis-Menten equation. (05 Mar 2000) |