<prompt> Repolarization of a nerve is due to: September 2009Hydrogen ionsPotassium ionsSodium ionsCalcium ions  <response>: Ans. B: Potassium ionsThe Na channels rapidly enter the inactivated state and remain in this state for a few milliseconds before returning to the resting state. In addition, the direction of the electrical gradient for Na is reversed during the overshoot because the membrane potential is reversed, and this limits Na influx.A third factor producing repolarization is the opening of voltage-gated K channels.The net movement of positive charge out of the cell due to K efflux at this time helps complete the process of repolarization.The slow return of the K channels to the closed state also explains the after-hyperpolarization. 