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1. Capable of doing or being, although not yet doing or being; possible, but not actual. 2. A state of tension in an electric source enabling it to do work under suitable conditions; in relation to electricity, p. is analogous to the temperature in relation to heat. [L. potentia, power, potency]
action p. the change in membrane p. occurring in nerve, muscle, or other excitable tissue when excitation occurs.
after-p. See afterpotential.
bioelectric p. electrical p.'s occurring in living organisms.
biotic p. a theoretical measurement of the capacity of a species to survive or to compete successfully.
brain p. the electrical charge of the brain as compared to a point on the body; the p. may be steady (DC p.) or may fluctuate at specific frequencies when recorded against time, giving rise to the electroencephalogram.
chemical p. (mu) a measure of how the Gibbs free energy of a phase depends on any change in the composition of that phase.
demarcation p. the difference in p. recorded when one electrode is placed on intact nerve fibers or muscle fibers and the other electrode is placed on the injured ends of the same fibers; the intact portion is positive with reference to the injured portion.injury p;
early receptor p. (ERP) a voltage arising across the eye from a charge displacement within photoreceptor pigment, in response to an intense flash of light.
evoked p. an event-related potential, elicited by, and time-lockied to a stimulus. See also evoked response.
excitatory junction p. (EJP) discrete partial depolarization of smooth muscle produced by stimulation of excitatory nerves; similar to small end-plate p.'s. They summate with repeated stimuli.
excitatory postsynaptic p. (EPSP) the change in p. which is produced in the membrane of the next neuron when an impulse which has an excitatory influence arrives at the synapse; it is a local change in the direction of depolarization; summation of these p.'s can lead to discharge of an impulse by the neuron.
generator p. local depolarization of the membrane p. at the end of a sensory neurone in graded response to the strength of a stimulus applied to the associated receptor organ, e.g., a pacinian corpuscle; if the generator p. becomes large enough (because the stimulus is at least of threshold strength), it causes excitation at the nearest node of Ranvier and a propagated action p.
inhibitory junction p. (IJP) hyperpolarization of smooth muscle produced by stimulation of inhibitory nerves.
inhibitory postsynaptic p. (IPSP) the change in p. produced in the membrane of the next neuron when an impulse which has an inhibitory influence arrives at the synapse; it is a local change in the direction of hyperpolarization; the frequency of discharge of a given neuron is determined by the extent to which impulses that lead to excitatory postsynaptic p.'s predominate over those that cause inhibitory postsynaptic p.'s.
injury p. demarcation p
membrane p. the p. inside a cell membrane, measured relative to the fluid just outside; it is negative under resting conditions and becomes positive during an action p.transmembrane p;
myogenic p. action p. of muscle.
oscillatory p. the variable voltage in the positive deflection of the electroretinogram (B-wave) of the dark-adapted eye arising from amacrine cells.
Ottoson p. electro-olfactogram
oxidation-reduction p. (E0+, E0, Eh) the p. in volts of an inert metallic electrode measured in a system of an arbitrarily chosen ratio of [oxidant] to [reductant] and referred to the normal hydrogen electrode at absolute temperature; it is calculated from the following equation: where R is the gas constant expressed in electrical units, T the absolute temperature (Kelvin), n the number of electrons transferred, F the faraday and E0 the normal symbol for the p. of the system at pH 0; for biological systems E0´ is often used (in which pH = 7). Cf. Nernst's equation. redox p;
pacemaker p. the voltage inscribed by impulses from an artificial electronic pacemaker.
redox p. oxidation-reduction p
S p. prolonged, slow, depolarizing or hyperpolarizing responses to illumination; initiated between the photoreceptor and ganglion cell layers of the retina.
somatosensory evoked p. the computer-averaged cortical and subcortical responses to repetitive stimulation of peripheral nerve sensory fibers.
spike p. the main wave in the action p. of a nerve; it is followed by negative and positive afterpotentials.
thermodynamic p. See free energy.
transmembrane p. membrane p
visual evoked p. voltage fluctuations that may be recorded from the occipital area of the scalp as the result of retinal stimulation by a light flashing at 1 / 4-second intervals; commonly summated and averaged by computer.
zeta p. the degree of negative charge on the surface of a red blood cell; i.e., the p. difference between the negative charges on the red cell and the cation in the fluid portion of the blood.
zoonotic p. the p. for infections of subhuman animals to be transmissible to humans.
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