Action potentials are normally carried in only one direction: from the axon hillock toward the axon terminals. If you experimentally depolarize the middle of the axon to threshold, using an electronic probe, then .

from the axon hillock toward the axon terminals.

Explanation:

Axon hillock is a cone-shaped elevation of an axon. It is the region where axons join the cell body. In most neurons, nerve impulses arise at the junction of the axon hillock and the initial segment of axons. This region is called the trigger zone. From this region, a nerve impulse travels towards axon terminals. Axon terminals may have synaptic end bulbs at their tips. As nerve impulse travel from axon hillock to the axon terminal, synaptic vesicles having neurotransmitters are released into the synaptic cleft.