<P> In neuroscience, repolarization refers to the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential has changed the membrane potential to a positive value . The repolarization phase usually returns the membrane potential back to the resting membrane potential . The efflux of K ions results in the falling phase of an action potential . The ions pass through the selectivity filter of the K channel pore . There are several K channels that contribute to repolarization, including A-type channels, delayed rectifiers, and Ca - activated K channels . </P> <P> Repolarization typically results from the movement of positively charged K ions out of the cell . The repolarization phase of an action potential initially results in hyperpolarization, attainment of a membrane potential, termed the afterhyperpolarization, that is more negative than the resting potential . Repolarization usually takes several milliseconds . </P>

What ion drives the membrane potential back to resting membrane potential (repolarization)