<prompt> Hyperpolarization is caused by which ions -KNaCa-HCO3  <response>: Ans. is a i.e., K o During depolarization spike potential there is opening of Na channels causing Na influx. This causes membrane potential to become 35 to 40 mV from -70 mV of resting potential,o During repolarization phase channels open and there is K efflux. The membrane voltage falls back repolarizes to resting potential, i.e., -70 mV. At this voltage. K channels close, but quite slowly. Therefore, more K ions leak out, causing a brief period in which the voltage falls below -70 mV, i.e. hyperplorization.o Then, KNa pump works to re-establish resting potential by pumping N ions back out and K. ions back into the cells. 