<Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> The axon hillock is a specialized part of the cell body (or soma) of a neuron that connects to the axon . </P> <P> 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 . </P> <P> The axon hillock also functions as a tight junction, since it acts as a barrier for lateral diffusion of transmembrane proteins, GPI anchored proteins such as thy1, and lipids embedded in the plasma membrane . </P>

Where is an action potential initiated in a neuron