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Depolarization
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{{Short description|Change in a cell's electric charge distribution}} {{Other uses}} {{Use American English|date=December 2020}} {{Use mdy dates |date=September 2020}} In [[biology]], '''depolarization''' or '''hypopolarization'''<ref name="Zuckerman">{{Cite book|url=https://books.google.com/books?id=TA01Duy4RLwC&q=%22Hypopolarization%22+depolarization&pg=PA172|title=Psychobiology of Personality|last=Zuckerman|first=Marvin|date=1991-05-31|publisher=Cambridge University Press|isbn=9780521359429|language=en}}</ref><ref name="Gorsuch">{{Cite book|url=https://books.google.com/books?id=PrNCrbr7fyMC&q=%22Hypopolarization%22+depolarization&pg=PA152|title=Environmental Toxicology and Risk Assessment: 2nd volume|last=Gorsuch|first=Joseph W.|date=1993-01-01|publisher=ASTM International|isbn=9780803114852|language=en}}</ref> is a change within a [[cell (biology)|cell]], during which the cell undergoes a shift in [[electric charge]] distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is essential to the function of many cells, communication between cells, and the overall [[physiology]] of an organism. [[File:1221 Action Potential.jpg|thumb|right|[[Action potential]] in a [[neuron]], showing depolarization, in which the cell's internal charge becomes less negative (more positive), and repolarization, where the internal charge returns to a more negative value.]] Most cells in higher organisms maintain an internal environment that is negatively charged relative to the cell's exterior. This difference in charge is called the cell's [[membrane potential]]. In the process of depolarization, the negative internal charge of the cell temporarily becomes more positive (less negative). This shift from a negative to a more positive membrane potential occurs during several processes, including an [[action potential]]. During an action potential, the depolarization is so large that the potential difference across the cell membrane briefly reverses polarity, with the inside of the cell becoming positively charged. The change in charge typically occurs due to an influx of [[sodium]] [[ion]]s into a cell, although it can be mediated by an influx of any kind of [[cation]] or efflux of any kind of [[anion]]. The opposite of a depolarization is called a [[hyperpolarization (biology)|hyperpolarization]]. Usage of the term "depolarization" in biology differs from its use in physics, where it refers to situations in which any form of [[Polarization (disambiguation)#In the physical sciences|polarity]] ({{hsp}}''i.e.'' the presence of any electrical charge, whether positive or negative) changes to a value of zero. Depolarization is sometimes referred to as "hypopolarization"<ref name="Zuckerman"/><ref name="Gorsuch"/> (as opposed to hyp'''er'''polarization).
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