Axon

Axon (neuritum)

NervousNervesWhole body

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What it is

The single long output fibre. It leaves the soma at a cone-shaped axon hillock, runs inside its myelin sheath and ends in terminal branches at the synapse.

Function

Conducts the action potential - an all-or-nothing electrical impulse - away from the cell body, and transports proteins and organelles along its length in both directions.

Size

1-20 micrometres thick; from under 1 mm to over 1 m long (spinal cord to big toe)

Clinical note

After a peripheral nerve injury the axon can regrow about 1 mm a day inside its old sheath, which is why feeling returns to the fingertips months after a wrist injury.