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In biology, depolarization is a positive-going 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. The membrane potential is reduced by the removal of some of the electrical charge.  Hyperpolarization is the opposite of depolarization, and inhibits the rise of an action potential. This rise of an action potential is also known as the threshold of excitation. 
If, for example, a cell has a resting potential of –70mV, once 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.
Expand on the mechanism, potentially mentioning repolarization, resting potential, etc. Look for picture of charges inside and outside of a neuron.
There are drugs, called depolarization blocking agents, that cause prolonged depolarization by opening channels responsible for depolarization and not allowing them to close, preventing repolarization. Examples include the nicotinic agonists suxamethonium and decamethonium.
Research more information regarding these blockers so this section may be a bit more specific. Possibly find empirical articles to use.
Depolarization in the Heart
Here is where depolarization of the heart will be briefly mentioned and then will be compared to depolarization of neurons in the brain. Another picture could be useful as well.
- Purves D, Augustine GJ, Fitzpatrick D; et al., eds. (2001). Neuroscience (2. ed.). Sunderland, Mass: Sinauer Assoc. ISBN 0-87893-742-0.
- "Depolarization (Animation)". Psychology Department, Hanover College. Retrieved 18 May 2013.
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