axonsegmenten

Axonsegmenten (axon segments) are portions of an axon bounded by interruptions in its myelin sheath or by points where it branches.

In myelinated axons, the axon is divided into internodes—the myelinated segments—separated by nodes of Ranvier. Myelination is produced by oligodendrocytes in the central nervous system and by Schwann cells in the peripheral nervous system. The membrane under the myelin sheath has high electrical resistance and low capacitance, facilitating rapid signal transmission. Nodes of Ranvier contain concentrated voltage-gated sodium and potassium channels that support action potential regeneration.

Functionally, axon segments enable fast conduction through saltatory conduction, where the impulse effectively leaps from node to node. The length of segments, the thickness of the myelin, and the diameter of the axon influence conduction velocity and energy efficiency. Longer internodal segments and thicker myelin generally increase speed, while larger-diameter axons also conduct more rapidly.

Relevance and variation: changes in axon segment structure occur during development and in disease. Demyelinating conditions disrupt internodal segments and impair signal propagation, contributing to neurological deficits. In research and modeling, the concept of axon segments helps characterize electrical signaling, axonal transport, and the integrity of myelin in imaging studies.