Hyperpolarization (biology)

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Hyperpolarization is a change in a cell's membrane potential that makes it more negative. It is the opposite of a depolarization. It inhibits action potentials by increasing the stimulus required to move the membrane potential to the action potential threshold.

Hyperpolarization is often caused by efflux of K⁺ (a cation) through K⁺ channels, or influx of Cl^– (an anion) through Cl^– channels. On the other hand, influx of cations, e.g. Na⁺ through Na⁺ channels or Ca²⁺ through Ca²⁺ channels, inhibits hyperpolarization. If a cell has Na⁺ or Ca²⁺ currents at rest, then inhibition of those currents will also result in a hyperpolarization. This voltage-gated ion channel response is how the hyperpolarization state is achieved. In neurons, the cell enters a state of hyperpolarization immediately following the generation of an action potential. While hyperpolarized, the neuron is in a refractory period that lasts roughly 2 milliseconds, during which the neuron is unable to generate subsequent action potentials. Sodium-potassium ATPases redistribute K⁺ and Na⁺ ions until the membrane potential is back to its resting potential of around –70 millivolts, at which point the neuron is once again ready to transmit another action potential.^[1]