Axon

An axon is a long, slender part of a nerve cell, or neuron.

You can think of it as a primary transmission line for the nervous system. Its main job is to carry electrical impulses, called action potentials, away from the cell body. These signals travel to other neurons, muscles, or even glands. While dendrites are parts of a neuron that receive signals, axons are the parts that transmit them.

This clear division helps the nervous system organize how information flows through your body.

To work, the axon uses a special internal transport system. Inside the axon is a liquid called axoplasm. Tiny tracks called microtubules run along the length of the axon. These tracks act like a road for moving important materials. One type of motor protein, called kinesin, carries things outward toward the end of the axon. Another protein, called dynein, carries waste materials back to the cell body.

This constant movement keeps the long axon healthy and growing.

Most axons end in many tiny branches called telodendria. At the very tips are swollen parts called axon terminals. These terminals reach out to touch other cells at junctions called synapses.

At a synapse, the axon membrane sits very close to a target cell. Special molecular structures then pass the electrical or chemical signals across the tiny gap. Some axons even have hundreds or thousands of these small junctions, called en passant boutons, along their entire length. This allows one single axon to talk to many different parts of the brain at once.

Axons come in many different sizes and shapes. Most are microscopic, with a diameter of about one micrometer. However, some are much larger. The squid has a giant axon that is nearly 1 millimeter wide. That is about the size of a small pencil lead!

In humans, the longest axons are in the sciatic nerve. These run all the way from the base of the spine to the big toe. Many axons are also wrapped in a fatty layer called myelin. This layer acts like insulation on an electrical wire.

In the brain, these bundled, insulated axons create the white matter.

This insulation helps signals move much faster through a process called saltatory conduction. The myelin sheath is not a solid tube, though. It has small, unmyelinated gaps called nodes of Ranvier. The electrical signal jumps between these gaps to speed things up. In the central nervous system, cells called oligodendrocytes create this myelin. In the rest of the body, cells called Schwann cells do the job.

These tiny structures work together to make sure your brain and body stay connected.