depolarization(redirected from phase 4 depolarization)
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Related to phase 4 depolarization: pacemaker cell
the reduction of a membrane's resting potential so that it becomes less negative. In cardiac physiology there are several forms: the normal slow diastolic depolarization of pacemaker cells; the slow but normal depolarization of cells of the atrioventricular and sinoatrial nodes; the rapid phase 0 depolarization of normal atrial, His-Purkinje, and ventricular cells; and abnormal depolarization resulting from disease.
phase 4 depolarization the slow reduction of the membrane potential during phase 4 (electrical diastole); normal in pacemaker cells but sometimes abnormally accelerated.
rapid depolarization the sudden reversal in electrical potential from negative to positive; it is represented by phase 0 of the action potential.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
1. A relative reduction in magnitude of polarization; in nerve cells, depolarization may result from an increase in the permeability of the cell membrane to sodium ions.
2. The destruction, neutralization, or change in direction of polarity.
Farlex Partner Medical Dictionary © Farlex 2012
1. The sudden change in electrical potential from negative to slightly positive which occurs during phase O of an action potential in an excitable cell membrane–in nerve and heart muscle.
2. A rapid alteration of the resting potential in a large mass of tissue–eg, heart ventricles, which usually results in a contraction. See Action potential, Latency period, Resting potential.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.
The destruction, neutralization, or change in direction of polarity.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
depolarizationThe immediate cause of the formation of a nerve impulse. Nerve fibres normally carry a positive charge of some 70 millivolts on the outside of the fibre, which is balanced by an equal negative charge on the inside. When movement of potassium ions causes a local reversal of this polarization, the fibre is said to be depolarized. A zone of depolarization then passes along the fibre. This is the nerve impulse.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
depolarizationthe process of reversing the charge across a cell membrane (usually a NEURON), so causing an ACTION POTENTIAL. In depolarization, the inside of the membrane, which is normally negatively charged, becomes positive and the outside negative. This is brought about by positive sodium ions rapidly passing into the axon. The RESTING POTENTIAL is restored by the SODIUM PUMP mechanism.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
A change in the value of the resting membrane potential towards zero. The inside of the cell becomes less negative compared to the outside. This is due to a change in permeability and migration of sodium ions into the interior of the cell. Depolarization is excitatory because the membrane potential shifts towards the neuron's threshold at which an action potential occurs. See hyperpolarization; synapse.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
Destruction, neutralization, or change in direction of polarity.
Medical Dictionary for the Dental Professions © Farlex 2012