Axon hillock

Axon hillock
Red labeled is pointing directly at the axon hillock.
Details
Part of	Axon of a nerve
System	Nervous system
Identifiers
Latin	colliculus axonis
TH	H2.00.06.1.00006
Anatomical terminology [edit on Wikidata]

The axon hillock is a specialized part of the cell body (or soma) of a neuron that connects to the axon. It can be identified using light microscopy from its appearance and location in a neuron and from its sparse distribution of Nissl substance.^[1]

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.^[2] For many years, it was believed that the axon hillock was the usual site of initiation of action potentials—the trigger zone. It is now thought that the earliest site of action potential initiation is at the axonal initial segment: just between the peak of the axon hillock and the initial (unmyelinated) segment of the axon.^[3] However, the positive point, at which the action potential starts, varies between cells.^{[citation needed]} It can also be altered by hormonal stimulation of the neuron, or by second messenger effects of neurotransmitters.^{[citation needed]}

The axon hillock also delineates separate membrane domains between the cell body and axon.^[4] This allows for localization of membrane proteins to either the axonal or somal side of the cell.