Axon hillock

The axon hillock is a specialized part of the cell body (or soma) of a neuron that connects to the axon.

The axon hillock is the last site in the soma where membrane potentials propagated from synaptic inputs are summated before being transmitted to the axon. For many years, it had been believed that the axon hillock was the usual site of action potential initiation. It is now thought that the earliest site of action potential initiation is found just adjacent, in the initial (unmyelinated) segment of the axon. However, the positive point, at which the action potential starts, varies between cells. It can also be altered by hormonal stimulation of the neuron, or by second messenger effects of neurotransmitters.