Final answer:
The statement is true; an action potential travels in one direction because voltage-gated Na+ channels behind it are in an absolute refractory state and cannot immediately reopen, preventing reverse propagation.
Step-by-step explanation:
The statement that an Action Potential will ONLY propagate in the "forward" direction is True because voltage-gated Na+ channels in the "backward" direction are in a refractory state. As the action potential moves down the axon, these channels enter an absolute refractory period during which they cannot reopen, preventing the action potential from moving in the reverse direction.
During this period, the gates of these channels are closed and they are inactivated. Only after the membrane potential has returned close to the resting potential do these Na+ channels transition from the inactivated state to the closed, or resting, state, which signifies the end of the refractory period. Consequently, only then can they respond to a new stimulus, provided that the stimulus is relatively stronger due to the ongoing efflux of K+ from the cell, which characterizes the relative refractory period.