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

/de·po·lar·iza·tion/ (de-po″lahr-ĭ-za´shun)
1. the process or act of neutralizing polarity.
2. in electrophysiology, reversal of the resting potential in excitable cell membranes when stimulated.

atrial premature depolarization  (APD) see under complex.
ventricular premature depolarization  (VPD) see under complex.

depolarization

[dēpō′lərīzā′shən]
the reduction of a membrane potential to a less negative value. It is caused by the influx of cations, such as sodium and calcium, through ion channels in the membrane. In many neurons and muscle cells, depolarization may lead to an electric impulse called an action potential.

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

reduction of the normal voltage difference between the inside and the outside of a cell. See also action potential, membrane potential.

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.

depolarization (dēpō´lərizā´shən),

n a neutralization of polarity; the breaking down of polarized semipermeable membranes, as in nerve or muscle cells in the induction of impulses.

depolarization

the process or act of neutralizing polarity as in the decrease of membrane potential.

myocardial depolarization
the conducted cardiac impulse transiently reverses membrane polarity. In this depolarized phase the myocardium is incapable of further contraction.
References in periodicals archive ?
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.
18) We have calculated the MEA from the vectors of ventricular depolarization in leads H and III by using the Bailey hexaxial system.
In conclusion, our results demonstrate that tacrine-induced depolarization of mitochondria initiates ROS formation and the excessive production of ROS creates a situation of oxidative bursts and thus causes mtDNA damage, further mitochondrial dysfunction and cytotoxicity.
These results suggested that both ECON and ECAP trials did not result in the prolongation of the QT and/or RT intervals during postexercise recovery, indicating no adverse effect upon cardiac depolarization and repolarization process.
Stimulation of the hair bundle, as we have seen, causes membrane depolarization, neurotransmitter release, and action potential discharges in auditory nerve fibers.
The PRK 25B opto-electronic sensor range comes in three basic variants, a retro-reflective unit with a large sensing distance up to 10m ideal for standard applications, a depolarization sensor for detection of stretch or shrink-wrapped items with a range of 8m, and a laser version for greater precision over a distance of 15m.
The product was found to inhibit the depolarization of sensory nerve cells upon stress.
Procoralan is the first pure heart rate-lowering agent and acts by selective inhibition of the cardiac pacemaker If current that controls the spontaneous diastolic depolarization in the sinus node and regulates heart rate.
At this level of accuracy no depolarization was observed.
Rather than inducing a stroke, the small embolus or platelet plug precipitates a spreading wave of depolarization that is recognized as the neurologic phenomenon of migraine," Dr.
The optimized geometries, conformational stabilities, infrared intensities, Raman Activities, depolarization ratios and vibrational wave number have been obtained from MP2/6-31G(d) ab initio calculations.