Axon

Definition

The long, slender projection of a neuron that conducts electrical impulses (action potentials) away from the cell body toward other neurons, muscles, or glands. In arthropods, axons vary dramatically in caliber and conduction velocity; giant axons in the ventral nerve cord of insects and crustaceans enable rapid escape responses, while fine unmyelinated axons predominate in the dense neuropils of the brain and sensory ganglia.

Etymology

From Greek ἄξων (axōn), meaning 'axis' or 'axle', referring to the central conducting shaft of the nerve fiber.

Example

In the American cockroach (Periplaneta americana), a pair of giant axons in the ventral nerve cord run the length of the body and mediate the rapid leg movements of the escape response when activated by wind-sensitive cercal hairs.

Synonyms

• nerve fiber
• neurite

Related Terms

• Dendrite
• Synapse
• Action potential
• myelin
• neuropil
• ganglion
• Ventral nerve cord

Usage Notes

Distinguished from dendrites, which typically conduct signals toward the cell body. In invertebrate neurobiology, 'axon' often implies the entire output process including collaterals, whereas 'neurite' is sometimes preferred when polarity is unclear (e.g., in developing or regenerating neurons). Giant axons are a classic preparation in invertebrate neurophysiology due to their large diameter, which allows stable intracellular recording.