Axons

An axon is a slender, elongated projection of a neuron that conducts electrical impulses away from the cell body. Axons can vary greatly in length, with some extending over long distances to reach distant targets. The axon typically originates at the axon hillock, where the initial segment near the soma is specialized for initiating action potentials.

Structure and components: The axon is enclosed by a membrane called the axolemma and contains axoplasm, a cytoplasm rich in microtubules, neurofilaments, and other proteins that support transport and structure. At its distal end, the axon forms synaptic terminals or boutons that establish chemical or electrical contacts with target cells. The axon is often insulated by myelin, produced by Schwann cells in the peripheral nervous system or oligodendrocytes in the central nervous system, which increases conduction velocity. Gaps in the myelin known as the nodes of Ranvier are rich in voltage-gated sodium channels and enable saltatory conduction.

Axonal transport and signaling: Materials such as organelles, vesicles, and signaling molecules are transported along the axon by microtubule-based motor proteins. Anterograde transport moves cargo from the soma to the terminal, while retrograde transport returns signals and used components to the cell body. This transport supports growth, maintenance, and communication.

Function and clinical relevance: Action potentials propagate along the axon to trigger neurotransmitter release at the synapse, conveying information to other neurons or effector cells. Axonal integrity is essential for neural communication; damage can lead to impaired signaling and degeneration. Conditions such as demyelinating diseases, peripheral neuropathies, and axonal injuries illustrate the clinical importance of axons.