action potential

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action potential

 
the electrical activity developed in an excitable cell when stimulated; it may be elicited by electrical, chemical, or mechanical stimulation, by temperature change, and so on.

On an electrocardiogram, action potential is seen as the cardiac cycle of a single cell, produced by a rapid sequence of changes at the cell membrane, and consists of phase 0 to phase 4, with phases 0 to 3 representing electrical systole and phase 4 representing electrical diastole. The characteristics of action potentials vary in different parts of the heart; for example, the cells of the sinoatrial and atrioventricular nodes and the atrial cells do not have phases 1 or 2 and are shorter in duration than those of the His-Purkinje system and the ventricles.
depressed fast response action potential an action potential produced when some but not all of the fast sodium channels are available to depolarize the fiber; on an electrocardiogram, it signifies the presence of slow conduction.
fast response action potential the action potential produced by a cell when all of the fast sodium channels are available for depolarization; on an electrocardiogram, it signifies rapid upstroke velocity and maximal amplitude for phase 0, with consequent optimal conduction velocity.
slow response action potential the action potential produced when only slow channels are available to depolarize the fiber; it is normal only in the sinoatrial and atrioventricular nodes and results in very slow conduction.

ac·tion po·ten·tial

the change in membrane potential occurring in nerve, muscle, or other excitable tissue when excitation occurs.

action potential

n.
A momentary change in electrical potential on the surface of a cell, especially of a nerve or muscle cell, that occurs when it is stimulated, resulting in the transmission of an electrical impulse.

action potential

an electric impulse consisting of a self-propagating series of polarizations and depolarizations, transmitted across the plasma membranes of a nerve fiber during the transmission of a nerve impulse and across the plasma membranes of a muscle cell during contraction or another activity. In the absence of an impulse, the inside is electrically negative and the outside is positive (the resting potential). During the passage of an impulse at any point on the nerve fiber, the inside becomes positive and the outside, negative. Also called action current.

Action Potential

An all-or-none electrical event (neural impulse) in an axon or muscle fibre in which the polarity of the membrane potential is rapidly reversed and re-established. Action potentials begin at one end of the axon of a neurone and move along the axon to the other end.
Action potential phases Phase 0 is the period of rapid depolarisation, the reversal of polarity from negative to slightly positive; the remaining 4 phases (1 through 4) are concerned with returning the cell to its resting membrane potential, where it remains until the next stimulus.

action potential

Cardiology The constellation of changes in electric potential generated by myocardial cell membranes after stimulation Physiology The sequential, electrochemical polarization and depolarization that traverses the membrane of a neuron in response to mechanical stimulation–eg, touch, pain, cold, etc. See Depolarization.

ac·tion po·ten·ti·al

(ak'shŭn pŏ-ten'shăl)
The change in membrane potential occurring in nerve, muscle, or other excitable tissue when excitation occurs.

action potential

The electrical signal propagated in nerve and muscle cells. It consists of a zone of reversal of the normal charge on the membrane so that the outside briefly becomes negative relative to the inside, instead of vice versa. This zone of depolarization, which is caused by the opening of ion channels, then moves along the fibre at a rate very much slower than the speed of normal electrical conduction along a wire. Action potentials operate according to an ‘all-or-none’ law. They function fully or not at all.

action potential

the electrical potential present between the inside and outside of a nerve or muscle fibre when stimulated. In the resting state (RESTING POTENTIAL) the muscle or the nerve fibre is electrically negative inside and positive outside. With the passage of the impulse the charges are reversed and the wave of potential change which passes down the fibre is the most easily observable aspect of an impulse. The impulse (DEPOLARIZATION) is short-lived and lasts for about 1 millisecond, after which time the resting potential is restored. see NERVE IMPULSE.

action potential

all-or-nothing response made by an excitable cell in response to a stimulus

ac·tion po·ten·ti·al

(ak'shŭn pŏ-ten'shăl)
The change in membrane potential occurring in nerve, muscle, or other tissue excitation.

action potential,

n 1. an electric impulse consisting of a self-propagating series of polarizations and depolarizations, transmitted across the cell membranes of a nerve fiber during the transmission of a nerve impulse and across the cell membranes of a muscle cell during contraction.
n 2. the electrical potential developed in a muscle or nerve during activity.

action potential

the nerve impulse, the sign of activity and the basis of activity in individual neurons in the nervous system. The measure of the activity of an individual nerve cell is indicated by the frequency of its discharge.

compound action potential
the sum of the activity in a number of nerve fibers. It applies to the degree of activity in a nerve trunk in which a variable proportion of nerve fibers are discharging.
References in periodicals archive ?
Only excitable tissues are able to generate action potentials that propagate from the point of origin to distant regions of the cell.
A monopolar electrode is used to stimulate the top of the inserted pedicle screw with needle electrodes measuring action potentials in the corresponding muscle groups.
Action potential is equivalent to the active response of the neuron, which can be modeled based on the Hodgkin-Huxley equivalent circuit model using variable resistors representing voltage-dependent ion channels.
Electrophysiological properties of neurons in intact rat dorsal root ganglia classified by conduction velocity and action potential duration.
11] JJ Torres, LN Cornelisse, EGA Harks, DL Ypey, and AP Theuvenet, "Modelling action potential generation and propagation in NRK Fibroblasts", AM J Physiol, Cell Physiol.
Wikswo & van Egeraat (1991) measured the action current associated with a propagating action potential along a squid giant axon using the same method described for the frog sciatic nerve bundle, and obtained I = 6 [micro]A.
1985), resulting in changed shape of the action potentials (Basmajin and DeLuca 1985).
The quick passing of the object from person to person across the gaps is similar to the "jumping" of action potentials down a myelinated axon.
It is well-established now that the PR interval is mainly dependent on the slow action potentials elicited on the AV node (Prystowsky, 1988; Golovko and Tipans, 1986; Brown et al.
However, significant differences were seen between the primiparous and the nulliparous subjects in the motor unit action potentials recorded by EMG.
The cochlear nerve continues to fire action potentials in the absence of sound; this is called spontaneous activity.
We report a case of West Nile poliomyelitis with preserved deep-tendon reflexes, diminished sensory nerve action potentials, and pathologic findings which do not localize to the anterior horn.

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