Axon structure, signaling, and clinical relevance

Axon definition and core functions

An axon is a long, slender projection of a neuron found in most animals. It typically conducts electrical impulses called action potentials away from the cell body and transmits information to other neurons, muscles, and glands. In sensory neurons (such as pseudounipolar neurons), impulses can travel from the periphery to the cell body and then onward to the spinal cord. Axons are one of two main types of neuronal cytoplasmic protrusions (the other being dendrites) and are distinguished by their shape, length, and their role in transmitting signals rather than receiving them. Core axonal functions include signal transmission via action potentials and synaptic communication. Axons may be myelinated or unmyelinated; myelination (by Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system) speeds conduction through saltatory conduction between nodes of Ranvier. The axonal initial segment (AIS) and axon hillock are specialized regions that help initiate action potentials, with a high concentration of voltage-gated sodium channels. Axons also support long-distance intracellular trafficking through axonal transport: anterograde transport delivers materials from the cell body to terminals, while retrograde transport returns waste to the cell body. At axon terminals, action potentials trigger neurotransmitter release, enabling synaptic connections (including synapses made along the axon via en passant boutons).

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Axon versus dendrite distinctions

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