(ak'son‵ , ak'sōn‵)

[Gr. axōn, axle, axis]

The long, slender process of a nerve cell (neuron) that contains neurofilaments, microtubules, and organelles. Axons make neurons the longest cells in the body; in humans, a microscopically thin axon can be more than 2 ft long. Axons arise from a portion of the cell body (the axon hillock) that has very few ribosomes. (The cytoplasm inside axons has no ribosomes at all.) All axonal proteins are made in the cell body and are actively transported down the axon (along with mitochondria, vesicles, and other organelles). The axon is structurally similar whether growing or stationary; however, when an axon is elongating, its end becomes a specialized motile organelle (the growth cone). When the axon stops at a target cell, its end turns into a secretory organelle (the presynaptic terminal).

Axons carry electrochemical impulses and are the “wires” of the nervous system. Inside the central nervous system, axons follow stereotypically located paths (tracts); in the peripheral nervous system, axons run inside stereotypically located nerves. Most axons conduct impulses anterogradely (away from their neuronal cell body). The notable exception is the dorsal root ganglion cell, which has an axon that branches, and , as one branch carries impulses anterogradely, the other branch carries impulses toward the cell body and acts like a dendrite.

SYN: nerve fiber; neuraxon.

SEE: nerve.

axonal,

(ak'sŏ-năl )