Explanation

In neurons, the restoration of resting potential is called repolarization. After depolarization, with the increase of sodium ions inside the nerve fibre, the membrane becomes less permeable to $Na^{+}$ and more to $K^{+}$. the $Na^{+}$ channels of axon membrane close and $K^{+}$ channels open. $Na^{+}$ influx stops and $K^{+}$ outflow starts until the original resting state of ionic concentration is achieved. Thus, resting potential is restored, which is called repolarization of the membrane. Until repolarization occurs, neuron cannot conduct another impulse. The time taken for this restoration is called refractory period.