List out the phases in action membrane potential.

Explanation

Action membrane potential: An action potential occurs when a neuron sends information down an axon, away from the cell body. It includes following phases, depolarization, repolarisation and hyper polarization.

Repolarisation [Falling Phase]: When the membrane reaches the spike potential, the sodium voltage-gate closes and potassium voltage-gate opens. It checks influx of `Na^+` ions and initiates the efflux of `K^+` ions which lowers the number of positive ions within the cell. Thus, the potential falls back towards the resting potential. The reversal of membrane potential inside the axolemma to negative occurs due to the efflux of `K^+` ions. This is called Repolarisation.
Hyperpolarization: If repolarization becomes more negative than the resting potential –70 mV to about – 90 mV, it is called Hyperpolarization. During this, `K^+` ion gates are more permeable to `K^+` even after reaching the threshold level as it closes slowly, hence called Lazy gates, The membrane potential returns to its original resting state when `K^+` ion channels close completely. During hyperpolarization the `Na^+` voltage gate remains closed.