Action Potential

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action potential

[′ak·shən pə‚ten·chəl]
(neuroscience)
A transient change in electric potential at the surface of a nerve or muscle cell occurring at the moment of excitation.

Potential, Action

 

rapid fluctuation of membrane potential arising in response to excitation of nerve and muscle cells or fibers; an active electrical signal by means of which information is transmitted in man and animals.

Action potential is based on rapidly reversible changes in the ionic permeability of the cell membrane that are caused by activation and inactivation of ionic membrane canals. In nerve fibers, the ascending phase of action potential is caused by activation of the rapid sodium canals, and the descending phase by inactivation of these canals and activation of the potassium canals. The same mechanism is reponsible for the generation of action potential in the fibers of vertebrate skeletal muscles.

Activation of the rapid sodium canals in myocardial fibers ensures only the initial surge of action potential: the plateau of action potential characteristic of these fibers is caused by activation of the slow sodium and calcium canals. Rapid sodium canals are not found in the membranes of smooth muscle fibers in the internal organs and blood vessels of vertebrates or in the membranes of muscle fibers of such arthropods as crustaceans and insects and in the membranes of some mollusk neurons. Action potential in these cells is stimulated by activation of the slow sodium and calcium canals or of the slow calcium canals. The descending phase of action potential is maintained by the potassium canals.

Study of the physicochemical properties of ionic canals is important both for interpreting their molecular structure and for developing methods of controlling the generation of action potential in various cells. The rapid sodium canals are specifically blocked by tetrodotoxin, derived from some species of puffer fish of the suborder Tetraodontoidea and from newts of the genus Taricha, as well as by Novocain, cocaine, and other local anesthetics. The slow sodium and calcium and slow calcium canals are not affected by these agents but are blocked by Mn2+, Co2+, Ni2+, and La3- ions and by such organic compounds as isoptin, used in cardiology, and its derivative D-600. Most of the potassium canals are effectively blocked by tetraethylammonium. The effect of action potential on such intracellular processes as the contraction of myofibrils in skeletal, smooth, and cardiac muscles and neurosecretion in some specialized neurons and nerve endings is triggered by the direct action of an electrical impulse on the intracellular structures (Ca2+ is released from the sarcoplasmic network of the muscle) and by the effect on these structures of Ca2+ ions penetrating into the cell during action potential.

B. I. KHODOROV

References in periodicals archive ?
Although it may be true that most neurons work to relay spikes as a part of spike waves, destination neurons in a communication task are limited in number and must select signals sent to them from among the various spike waves based on spike trains containing codes that are a fragment of each spike wave or a spatiotemporal combination of these codes.
Caption: Figure 7: An example of simulated spike trains caught by Em during 2.
The blue curve shows the average of trials of an experimental number of codes detected from 63 electrodes in spike trains during 200 ms after stimulation expressed with 2000 time bins of 0.
From the viewpoint of the coding scheme of spike trains, we showed that M-sequence-related codes are detected significantly more often than those from time-shuffled trains [14].
In this study, to clarify the spike-coding mechanism, we first analyzed the spike trains of cultured neural networks by examining the code of a multielectrode array.
Expanding this to 200 ms after stimulation, we obtained the histogram in Figure 3 of the sum of the "1011" and "1101" detected codes per trial among the 9 trials of Sample A, the 23 trials of Sample B, and the 26 trials of Sample C, in which we decoded spike trains from 63 electrodes excluding one stimulation electrode with various bit widths within 0.
Furthermore, we showed that if we shuffled the spike trains in interval orders or in electrodes, they became significantly small.
The analysis proposed here can also be regarded as the code decomposition of random-like spike trains with non-fully independent and semiorthogonal components (codes).
We can observe spike trains containing code such as "1011.
The first experiment tested a basic prediction of the multiplex filter model: If the spike train carries information about the Walsh function by adding together individual signals from the filters in one multiplexed signal, then the multiplexed signals for two Walsh functions, combined, should be the same as the signal produced in response to a pattern that is a combination of those two Walsh functions.
The multiplex filter hypothesis doesn't rule out neurons transmitting information simply by being more or less active, Mishkin says, but if the hypothesis is valid, scientists could be ignoring most of the information transmitted because they are ignoring the patterns in the spike train.