Initial (axon) segment


The first 5 -10 micrometers of the axon, precisely where it originates from the axon hillock, are called the "initial segment" - IS.

The initial segment, which is comparatively narrow, is very easily affected by electrochemical stimuli. This is where the information captured by the dendrites and the cell body can be made to give rise to nerve impulses/action potentials that spread out along the axon. Nerve endings that have synapses directly on the initial axon segment itself are therefore particularly important for the signaling behavior of the nerve cell.