Initiation of nerve impulse occurs at the axon hillock because:: (A) It has a lower threshold than the rest of the axon, (B) It is unmyelinated, (C) Neurotransmitter release occurs here, (D) None of the above
Answer is A. The membrane of the axon hillock/initial segment contains a high density of voltage-gated Na+ and K+ channels. These channels are fewer along the dendrites and cell body. The axon hillock has a lower threshold for firing an action potential. This region is also known as the trigger zone for the action potential. It requires a relatively low degree of depolarization for initiation of spike at the axon hillock/initial segment.