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 ?
ECAP and EABR thresholds and wave eV latencies obtained in EABR thresholds Mean[+ or -]Standard ECAP EABR Deviation threshold (CU) threshold (CU) Basal electrode 171.5[+ or -]11.38 169.69[+ or -]12.17 Medial electrode 169.69[+ or -]20.32 165.62[+ or -]16.41 Apical electrode 160.81[+ or -]20.03 160[+ or -]15.49 Mean[+ or -]Standard Wave eV latency at Deviation threshold (msec) Basal electrode 4.88[+ or -]0.4 Medial electrode 4.58[+ or -]0.32 Apical electrode 4.53[+ or -]0.35 ECAP: electrically compound action potentials; EABR: electrically evoked auditory brainstem response; CU: current unit; msec: millisecond Table 2.
Using evoked compound action potentials to assess activation of electrodes and predict c-levels in the tempo+ cochlear implant speech processor.
elegans into the ranks of spike-producing animals, the action potentials observed in this organism were not identical to those seen elsewhere.
The action potential is governed by the FHN-type model (4) in the form of two coupled equations:
Mitchell et al., "In vivo gene transfer of Kv1.5 normalizes action potential duration and shortens QT interval in mice with long QT phenotype," American Journal of Physiology-Heart and Circulatory Physiology, vol.
sidoides (EOL) and thymol on conduction velocity of compound action potential component.
Based on this, the current study utilised big data to establish a standardised heart outer membrane action potential mode and modulated this model with simple parameters, to enable this model to show different heart outer membrane action potential characteristics and reversely calculate this model with ECG eigenvalue.
The action potential firing process is as follows: (1) After postsynaptic neuron receiving impulse from presynaptic neuron, the neuron membrane increases its permeability to [Na.sup.+] changes and begins to depolarize (subthreshold activity); (2) permeability further increases, with enormous [Na.sup.+] flow inward, and membrane potential rises rapidly (suprathreshold activity); (3) permeability to [Na.sup.+] decreases and permeability to [K.sup.+] increases, and repolarization begins; (4) permeability to [K.sup.+] continues to increase and [K.sup.+] flows outward until hyperpolarization; (5) after permeability to [K.sup.+] decreases, membrane potential rises to a resting level.
reported that triiodothyronine (T3) treatment of mouse ESC-derived cardiomyocytes for 7 days increased expressions of cardiac-specific genes (such as Nkx2.5 and MLC2v) and led to a more adult-like action potential profil e and calcium handing [46].
One can therefore measure and record the action potential of individual cells using a special camera.
The recommended criteria for an abnormal study is: 1) a value for the mean MCD of 20 fiber pairs greater than the 95% upper confidence limit for that muscle; or 2) jitter values in more than 10% of pairs greater than the 95% upper CL for action potential pairs in a muscle (7).

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