Action Potential


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Related to Action Potential: membrane potential, Cardiac action potential

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 ?
The action potential is governed by the FHN-type model (4) in the form of two coupled equations:
sidoides (EOL) and thymol on conduction velocity of compound action potential component.
Singh, "A Comparative Study of Numerical Methods for the Hodgkin-Huxley Model of Nerve Cell Action Potentials.
In the evaluation of the amplitudes and latencies of sensory nerve action potentials and PCBm sensory conduction velocities according to the severity of CTS, while minimal correlation was found between CTS severity and PCBm conduction velocity (correlation coefficient of 0.
Each segment of the membrane experiencing an action potential has behind it a segment in a refractory state but, in front of it, a segment that is able to fire.
In order to evaluate the effects of R(+)-puIegone on the electrical properties of cardiac myocytes, we first studied its effect on the action potential waveform of isolated ventricular myocytes.
In particular, the slight redistribution of charge associated with the Lorentz magnetic force exerted on moving intracellular ions leads to formation of an induced Hall electric field in a direction perpendicular to that of action potential transmission along the axon.
This response pattern is different from the traditional all-or-none action potential described above.
Sheng, "Effects of berberine on ventricular fibrillation threshold and action potentials in rabbit myocardium in vivo," Clinical and Experimental Pharmacology, vol.
kr]), currently resulting in delayed phase 3 repolarization and prolongation of action potential duration.
The Action Potential Venture Capital (APVC) fund will complement the company's own in-house progress in the field, following the establishment of its bioelectronics R&D unit last year.
New investors Covidien Ventures, the venture capital investment arm of Covidien plc (NYSE:COV), Action Potential Venture Capital Limited, GlaxoSmithKline's (LON:GSK) new USD50m strategic venture capital, and Boston Scientific (NYSE:BSX) participated in the round together with existing investors.

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