mielinie

Mielinie, in Polish and other languages, refers to the myelin sheath of nerve fibers. The myelin sheath is a lipid-rich, insulating layer that surrounds many axons in the vertebrate nervous system and is essential for rapid signal transmission.

Structure and formation: In the central nervous system (CNS), myelin is produced by oligodendrocytes, each wrapping segments of several axons. In the peripheral nervous system (PNS), Schwann cells form myelin around a single axon. The sheath consists of multiple compact lamellae of glial plasma membrane, high in lipids and specialized proteins such as MBP and PLP in the CNS, and P0 and PMP22 in the PNS. Gaps in the sheath, called nodes of Ranvier, expose the axon membrane and contain a high density of voltage-gated channels to facilitate saltatory conduction.

Function: Myelin increases the speed of electrical impulses by reducing membrane capacitance and enabling saltatory conduction, thereby improving conduction velocity and energy efficiency. It also provides metabolic support and protects axons.

Development and turnover: Myelination begins in prenatal life and continues into adolescence, varying by region and neuron type. Myelin can be damaged and subsequently remyelinated, though remyelination may be incomplete in certain injuries or diseases.

Clinical significance: Demyelinating diseases disrupt nerve signaling. In the CNS, multiple sclerosis is a prominent example; in the PNS, Guillain-Barré syndrome is typical. Other disorders include leukodystrophies. Diagnosis often involves MRI and cerebrospinal fluid analysis, while treatment focuses on symptom management and, where possible, promoting remyelination.

See also: myelin, oligodendrocyte, Schwann cell, multiple sclerosis, leukodystrophy.