Briefly explain why the action potential flows only from the axon hillock to the terminal web.

Answer;
The action potential originates from the axon hillock which initiates the flow of the presence of higher density voltage-gated ion channels.

Explanation;
Action potentials are initiated at a low threshold (trigger zone) which is more excitable than any other part of the soma or dendrites. The trigger zone is located at the axon initial segment, called the axon hillock, contains the highest density of sodium gated voltage gated ion channels.