Myelin

Myelin is a specialized, multilayered membrane that wraps around selected axons in the nervous system. It is produced by glial cells, specifically oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. Myelin contains a high proportion of lipids along with specialized proteins, giving it electrical insulating properties .^1,2

Myelin is arranged in segments along an axon rather than forming one continuous covering. Small gaps between adjacent myelin segments are called nodes of Ranvier. At these nodes, voltage-gated ion channels are concentrated, allowing action potentials to be regenerated at intervals along the axon. This organization produces saltatory conduction and enables faster, more energy-efficient signaling than in comparable unmyelinated axons .^1,2

Myelin also participates in the long-term relationship between glial cells and axons. Myelinating glia provide metabolic and trophic support that helps maintain axonal integrity, so their functions extend beyond electrical insulation alone .^1,2

Myelin in the central and peripheral nervous systems serves a similar basic purpose but is produced by different glial cells. A single oligodendrocyte can form myelin around segments of multiple axons, whereas an individual myelinating Schwann cell forms one myelin segment around one peripheral axon. The myelin sheath refers specifically to the layered myelin wrapping surrounding an axonal segment .^1,2