<prompt> Initiation of nerve impulse occurs at the axon hillock because:It has a lower threshold than the rest of the axonIt is unmyelinatedNeurotransmitter release occurs hereNone of the above  <response>: The membrane of the axon hillockinitial 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 hillockinitial segment. 