myeliinin

Myeliinin is a term sometimes used to refer to the insulating layer surrounding many nerve fibers, more commonly known as myelin. In vertebrates, myelin is produced by oligodendrocytes in the central nervous system (CNS) and by Schwann cells in the peripheral nervous system (PNS). The sheath is highly enriched in lipids, with a significant but variable content of proteins that help stabilize the membrane and support signaling.

Structure and composition: Myelin forms multilayered wraps around axons, creating internodes separated by nodes of Ranvier. The lipid-rich sheath increases membrane resistance and reduces capacitance, facilitating rapid impulse transmission. In the CNS, key proteins include myelin basic protein (MBP) and proteolipid protein (PLP); in the PNS, major proteins include MPZ (myelin protein zero) and PMP22. The different protein complements contribute to tissue-specific properties and resilience.

Function: The primary role of myeliinin is to enable saltatory conduction, allowing electrical impulses to travel quickly along myelinated segments. It also provides metabolic and structural support to axons, helping to maintain integrity during signaling and over long distances.

Development and variation: Myelination begins in the late prenatal period and continues into adolescence, with regional and sensory-mystems differences in timing. CNS myelination tends to be more protracted and variable than PNS myelination.

Clinical relevance: Demyelinating diseases, such as multiple sclerosis (CNS) and Guillain-Barré syndrome (PNS), disrupt myeliinin, slowing or blocking nerve conduction. Injury and aging can also diminish myelin integrity. In the PNS, Schwann cells can promote some regeneration, whereas CNS repair is more limited.

See also: myelin sheath, nodes of Ranvier, saltatory conduction.