Final answer:
Hyperpolarization is an overshoot of the resting potential during the repolarization phase of an action potential, caused by delayed closing of K+ channels and the K+ equilibrium being below -70 mV.
Step-by-step explanation:
During an action potential, after the cell membrane depolarizes, it must repolarize to reset its resting potential. This process involves potassium ions (K+) moving out of the cell.
As K+ channels are slow to close, the membrane potential overshoots, causing a period known as hyperpolarization. Hyperpolarization occurs because K+ ions reach equilibrium when the membrane voltage drops below the typical resting potential of -70 mV. Eventually, the membrane potential returns to its resting state as these delayed potassium channels close, and the Na+/K+ pump restores the ion balance.