Question

Why does the AP not propagate backwards after it gets away from the axon hillock?

a. It does.
b. Because Na+ channels open so fast.
c. Because K+ channels open so fast.
d. Because of Na+ channel inactivation.
d. Because of K+ channel inactivation.

Answer 1

Voltage-gated Na+ channels become inactivated after reaching the peak of depolarization, which prevents the action potential from propagating backwards.

Step-by-step explanation:

The action potential is propagated down the axon because voltage-gated Na+ channels open and allow Na+ ions to enter the cell, leading to depolarization. However, after reaching the peak of depolarization, these Na+ channels become inactivated, which prevents them from being opened again for a brief period of time. As a result, the depolarization cannot propagate backwards towards previously opened channels, and the action potential must continue to propagate towards the axon terminals.