Depolarization

(electricity) The removal or prevention of polarization in a substance (for example, through the use of a depolarizer in an electric cell) or of polarization arising from the field due to the charges induced on the surface of a dielectric when an external field is applied.
(optics) The resolution of polarized light in an optical depolarizer.

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

A decrease in the electrical potential across a cell membrane. Depolarization occurs during an action potential when the potential difference across a cell membrane (especially that of a muscle fibre or neurone) becomes reversed. The inside of the cell loses its negative charge and becomes positive relative to the outside due to an influx of sodium ions. Compare resting membrane potential. See also hyperpolarization.

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

• myocardial d. — the conducted cardiac impulse transiently reverses membrane polarity. In this depolarized phase the myocardium is incapable of further contraction.

For other uses, see Depolarization (disambiguation).

Neuroscience portal

In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential. Hyperpolarization is the opposite of depolarization, and inhibits the rise of an action potential.

Contents 1 Mechanism 2 Depolarization blockers 3 References 4 External links

Mechanism

If, for example, a cell has a resting potential of -70mV, and the membrane potential changes to -50mV, then the cell has been depolarized. Depolarization is often caused by influx of cations, e.g. Na⁺ through Na⁺ channels, or Ca²⁺ through Ca²⁺ channels. On the other hand, efflux of K⁺ through K⁺ channels inhibits depolarization, as does influx of Cl^– (an anion) through Cl^– channels. If a cell has K⁺ or Cl^– currents at rest, then inhibition of those currents will also result in a depolarization.

Because depolarization is a change in membrane voltage, electrophysiologists measure it using current clamp techniques. In voltage clamp, the membrane currents giving rise to depolarization are either an increase in inward current, or a decrease in outward current.

Depolarization blockers

There are drugs, called depolarization blocking agents, that inhibit depolarization, e.g. by blocking the channels responsible for depolarization, or by opening K⁺ channels. Examples include the nicotinic agonists suxamethonium and decamethonium.^[1]

References

1. ^ Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4.  Page 149

External links

• Neuroscience - online textbook by Purves, et al.
• Basic Neurochemistry Molecular, Cellular, and Medical Aspects by Siegel, et al.

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)