Question

Identify the region where all $N{a}^{+}$ channels are reactivated but closed and all $K^{+}$ channels are open.

• A. D
• B. C
• C. B
• D. A

Answer 1

Answer: (C)

B

At the beginning of the action potential, the $N{a}^{+}$ channels open and $N{a}^{+}$ moves into the axon, causing depolarization. Repolarization occurs when the $K^{+}$ channels open and $K^{+}$ moves out of the axon. This creates a change in polarity between the outside of the cell and the inside. The impulse travels down the axon in one direction only, to the axon terminal where it signals other neurons. The refractory periods are due to the inactivation property of voltage-gated sodium channels and the lag of potassium channels in closing.