Mielinu

Mielinu is a term used in some contexts to refer to the myelin sheath, the lipid-rich insulating layer that surrounds axons in the vertebrate nervous system. Myelin enhances the speed and efficiency of electrical signal transmission along nerve fibers.

In the central nervous system, myelin is produced by oligodendrocytes, which wrap their membranes around multiple axons. In the peripheral nervous system, Schwann cells generate myelin by encasing individual axons. The sheath is organized into segments called internodes, separated by nodes of Ranvier, where the axon membrane is exposed. The myelin sheath comprises mostly lipids with specific proteins; in the CNS the major proteins include myelin basic protein (MBP) and proteolipid protein (PLP), while in the PNS proteins such as P0 and PMP22 play key roles.

The primary function of myelin is to insulate axons and accelerate action potential conduction through saltatory conduction, allowing signals to jump between nodes of Ranvier. This arrangement reduces energetic cost by decreasing the need for continuous ion pumping along the axon.

Developmentally, myelination begins before birth in many species and continues after birth into adolescence, with ongoing plasticity and, in some contexts, remyelination after injury. Disruptions to myelin can lead to neurological diseases; demyelinating conditions such as multiple sclerosis and various leukodystrophies impair signal transmission and can be monitored with magnetic resonance imaging. Therapeutic research often focuses on promoting remyelination and protecting existing myelin.