| 单词 | action potential | |||
| 释义 | action potentialaction potentialaction potentialac′tion poten`tialn. action potential- A brief electrical signal transmitted along a nerve or muscle fiber following stimulation.
Action Potentialaction potential[′ak·shən pə‚ten·chəl]Potential, Actionrapid 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 action potentialaction potentialOn 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. ac·tion po·ten·tialaction potentialAction PotentialAn 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 potentialCardiology 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)action potentialThe 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 potentialthe 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.ac·tion po·ten·ti·al(ak'shŭn pŏ-ten'shăl)action potential
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action potential - the local voltage change across the cell wall as a nerve impulse is transmitted