Question

what characterizes repolarization, the second phase of the action potential?
once the membrane depolarizes to a peak value of +30 mv, it repolarizes to its negative resting value of -70 mv.
before the membrane has a chance to reach a positive voltage, it repolarizes to its negative resting value of approximately -70 mv.
as the membrane repolarizes to a negative value, it goes beyond the resting state to a value of -80 mv.
once the membrane depolarizes to a threshold value of approximately -55 mv, it repolarizes to its resting value of -70 mv.

Explanation:

Action potential has three phases: depolarization (membrane potential becomes less negative, reaches a peak like +30 mV), repolarization (after depolarization peak, membrane potential returns to negative resting value), and hyperpolarization (temporarily more negative than resting value).

• Option 1: Correctly describes repolarization as going from depolarization peak (+30 mV) back to negative resting value (-70 mV).
• Option 2: Incorrect as membrane does reach positive voltage (depolarization peak) before repolarization.
• Option 3: Describes hyperpolarization (going beyond resting state to -80 mV), not repolarization.
• Option 4: -55 mV is threshold for depolarization initiation, not related to repolarization description.

Answer:

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.