Editing Hyperpolarization (biology) (section)

{{Short description|Change in a cell membrane potential causing it to become more negative}}
{{more citations needed|date=May 2013}}
{{Use American English|date=December 2020}}
{{Use mdy dates |date=December 2020}}
[[Image:Apshoot.jpg|thumb|right|300px|Diagram of membrane potential changes during an action potential]]'''Hyperpolarization''' is a change in a [[cell (biology)|cell's]] [[membrane potential]] that makes it more negative. Cells typically have a negative resting potential, with neuronal action potentials depolarizing the membrane. When the resting membrane potential is made more negative, it increases the minimum stimulus needed to surpass the needed threshold. Neurons naturally become hyperpolarized at the end of an [[action potential]], which is often referred to as the relative refractory period. Relative [[Refractory period (physiology)|refractory periods]] typically last 2 milliseconds, during which a stronger stimulus is needed to trigger another action potential. Cells can also become hyperpolarized depending on channels and receptors present on the membrane, which can have an inhibitory effect.

Hyperpolarization is often caused by efflux of [[potassium|K<sup>+</sup>]] (a [[cation]]) through [[potassium channel|K<sup>+</sup> channels]], or influx of [[chloride|Cl<sup>&ndash;</sup>]] (an [[anion]]) through [[chloride channel|Cl<sup>&ndash;</sup> channels]]. On the other hand, influx of [[cation]]s, e.g. [[sodium|Na<sup>+</sup>]] through [[sodium channel|Na<sup>+</sup> channels]] or [[Calcium|Ca<sup>2+</sup>]] through [[Calcium channel|Ca<sup>2+</sup> channels]], inhibits hyperpolarization. If a cell has Na<sup>+</sup> or Ca<sup>2+</sup> currents at rest, then inhibition of those currents will also result in hyperpolarization. This voltage-gated ion channel response is how the hyperpolarization state is achieved. <ref>Pack, Phillip E. "Cliffs AP Biology 3rd Edition"</ref>