During an action potential, the membrane potential returning toward the resting value as potassium exits the cell is called

• A. Depolarization
• B. Repolarization
• C. Hyperpolarization
• D. Plateau phase

Answer: (B)

Repolarization is the phase where the membrane potential moves back toward the resting value as potassium leaves the cell. After the peak of the action potential, voltage-gated potassium channels open and K+ exits the neuron, pulling the membrane potential from a positive level back toward the resting potential. This outward positive current counteracts the earlier inward Na+ current that caused depolarization. This step distinguishes itself from depolarization (the initial rise in membrane potential due to Na+ influx) and from hyperpolarization (when the membrane becomes more negative than resting), and from the plateau phase (a prolonged depolarization seen in cardiac cells due to Ca2+ influx).