Myelin Sheath

Description

Longitudinal profile of a myelinated peripheral nerve fiber highlights a central axon ensheathed by concentric myelin lamellae formed by a Schwann cell, with the outermost neurolemma and intermittent cytoplasmic clefts separating the compact wraps. Nodes of Ranvier interrupt the insulation at regular intervals, creating short, unmyelinated gaps between adjacent internodes. Paranodal myelin terminal loops abut each node, while the axolemma remains continuous from proximal to distal segment. Spatially, compact myelin sits circumferentially around the axon, and the nodes lie between successive Schwann cell domains. Saltatory conduction depends on this geometry: voltage-gated sodium channels cluster at the nodes of Ranvier while the internodal membrane is electrically insulated, so action potentials effectively regenerate node-to-node rather than continuously along the axolemma. That is the teaching point. Clinically, the same microanatomy explains why demyelinating neuropathies such as Guillain–Barré syndrome or inherited Charcot–Marie–Tooth disease slow conduction velocity and can produce conduction block, and why remyelination with shortened internodes changes waveform dispersion on nerve conduction studies. The Schwann cell association also cues the peripheral pattern, distinct from oligodendrocyte myelin in the CNS. Use this artwork for neuroanatomy and neurophysiology lectures, histology lab manuals introducing myelin and Schwann cells, or neurology and neurosurgery texts correlating nodal organization with electrophysiology and peripheral neuropathy. It also fits patient-facing materials on demyelination when paired with simplified diagrams of nerve conduction. Anatomical accuracy verified by SciePro's Medical Advisory Board.