axon

An axon is the long, thin tail that grows out of a nerve cell and carries the cell's outgoing message away from its body. A nerve cell, called a neuron, has a plump central part (the cell body, or soma) where it lives and makes decisions, a bushy crown of short branches that catch incoming signals, and then a single long fiber that leaves the body to deliver the cell's own reply. That fiber is the axon. Think of the neuron as a tiny radio station: the branches are its antennas listening for news, and the axon is the broadcast cable running out the door to send the station's own signal onward.

The axon's job is one-way output. A signal starts where the axon joins the cell body, then travels down the fiber as a fast electrical pulse, finally reaching tiny terminals at the far end that hand the message to the next cell across a narrow gap called a synapse. Axons can be astonishingly long for a single cell: some that run from your spinal cord down to a toe are nearly a meter from end to end. To move signals quickly over such distances, many axons are wrapped in myelin, a fatty insulating sheath that lets the pulse skip along and arrive sooner. Bundles of these fibers, grouped together, are what we casually call nerves.

Because the axon is the part that reaches out and connects, it is central to how the whole nervous system is wired. One neuron's axon can branch and touch thousands of other cells, and the precise pattern of which axon meets which target is what builds the circuits behind moving, sensing, remembering, and thinking. When an axon is cut or its myelin is damaged, messages slow down or stop, which is why injuries and diseases affecting axons can rob a person of movement or feeling.