axones

Axones, an alternate spelling for axons in some contexts, are the long, slender projections of neurons that conduct electrical impulses away from the cell body. Each axon arises from the axon hillock, extends to reach synaptic targets, and may branch into collateral fibers.

Most axons are insulated by myelin sheaths produced by glial cells: oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. Myelin speeds impulse conduction and enables saltatory transmission, with gaps at the nodes of Ranvier where the membrane is exposed.

Axons rely on active transport to move proteins, mitochondria, and other cargo between the soma and distal terminals. This transport uses microtubules and motor proteins, with kinesin mediating anterograde transport toward the synapse and dynein supporting retrograde transport.

At their distal ends, axons form synapses with other neurons, muscle fibers, or glandular cells. The axon terminal contains synaptic vesicles filled with neurotransmitters that are released in response to activity, enabling communication across the synaptic cleft.

Developmentally, axons extend from growth cones and are guided by molecular cues to reach their targets, establishing functional circuits. Injury triggers Wallerian degeneration of the distal segment; the peripheral nervous system has some regenerative capacity, whereas central axons generally do not.

Clinically, axon pathology contributes to several disorders, including axonopathies and neuropathies. Demyelinating conditions such as multiple sclerosis impair conduction along axons, while diseases like amyotrophic lateral sclerosis involve degeneration of motor neuron axons.