RanvierKnoten

RanvierKnoten are gaps in the myelin sheath along myelinated axons, exposing the axolemma at regular intervals. They separate adjacent myelin segments produced by Schwann cells in the peripheral nervous system or by oligodendrocytes in the central nervous system. Each node is a compact, highly specialized region that hosts a high density of voltage-gated sodium channels, enabling the regeneration of action potentials as they propagate along the axon.

Anatomy and location: Run through along the axon at intervals corresponding to internodes, with node lengths typically on the order of 0.5 to 2 micrometers and internodal distances ranging from tens to hundreds of micrometers depending on the nerve and species. The node is flanked by paranodal junctions, where axons connect with glial cells, and juxtaparanodal regions that contain potassium channels. Molecular components such as Caspr and contactin organize the axoglial junctions at the paranodes, helping to maintain node integrity and segregate ion channel populations.

Function: The primary role of RanvierKnoten is to enable saltatory conduction, where action potentials jump from one node to the next. This mechanism dramatically increases conduction velocity in myelinated fibers and reduces the metabolic cost of impulse transmission by limiting membrane depolarization to the nodes.

Development and plasticity: Nodes form during myelination and are stabilized by glial-axon adhesion molecules and cytoskeletal scaffolding. Channel localization and node spacing can adapt during development and in response to injury or disease.

Clinical relevance: Disruption of nodes or myelin is implicated in demyelinating diseases such as multiple sclerosis and in hereditary paranodal disorders. Autoimmune responses targeting nodal or paranodal proteins can contribute to neuropathies and encephalitides.

History: The structure and its functional significance were described in the late 19th century by Louis-Antoine Ranvier. In some German texts, the term RanvierKnoten is used to denote the same structure.