depolarization


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depolarization

 [de-po″lar-ĭ-za″shun]
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.

de·po·lar·i·za·tion

(dē-pō'lăr-i-zā'shŭn),
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.

depolarization

Cardiac pacing
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.

de·po·lar·i·za·tion

(dē-pō'lăr-ī-zā'shŭn)
The destruction, neutralization, or change in direction of polarity.

depolarization

The 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.
Depolarizationclick for a larger image
Fig. 129 Depolarization . Depolarization of a nerve fibre.

depolarization

the 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.

depolarization

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.

de·po·lar·i·za·tion

(dē-pō'lăr-ī-zā'shŭn)
Destruction, neutralization, or change in direction of polarity.
References in periodicals archive ?
The numerical simulations have been performed by changing the filling factor function, the depolarization factor, and the mixing model.
The PP experiment allows probing more narrowly distributed relaxation modes and, in the conceptual limit of a very narrow polarization window, the experimental depolarization current peak is supposed to correspond to a single mode of relaxation [13], We used polarization windows two degrees wide, and we tacitly assumed that this window isolated single relaxation processes.
Since weak depolarization of postsynaptic membrane and activation of postsynaptic [G.sub.q/11]-coupled receptors can be achieved by synaptic activity, [Ca.sup.2+]-assisted RER appears to be most relevant for synaptically-driven eCB-STD (see below) among CaER, RER and [Ca.sup.2+]-assisted RER.
We also detected a lengthening in APD90, with a larger relative change in repolarization time than in depolarization time.
integerrima fruit extract in doses of 100 and 200 mg/kg/daily increased the depolarization phase and reduced the repolarization phase of ventricular muscle in rat.
The estimation of the conductivity for HV insulation under polarization and depolarization test result can be expressed from the PDC value [11-15].
(18) We have calculated the MEA from the vectors of ventricular depolarization in leads H and III by using the Bailey hexaxial system.
The changes of the polarization of initially polarized light when it propagates through a turbulent atmosphere can be easily accounted for with the use of the degree of depolarization [34]
The depolarization curve is a part of the hysteresis loop between the points (0, [D.sub.r]) and (-[E.sub.c], 0), for p = 1 (Fig.
Since a calcium-based depolarization is elicited by the addition of lysozyme [12] as well as the lysozyme fragment, CB2 [8], to T.
Trapping parameters of electrons in the dielectric is determined by using the thermally stimulated depolarization current technique.
Spreading depression (SD) is the historical term used to describe intense neuronal and glial depolarization events that propagate within cortical or subcortical grey matter at a rate of 2-4 mm/min regardless of functional divisions or arterial boundaries [22].