Myelinatie

Myelinatie, often called myelination in English, is the biological process by which glial cells form a myelin sheath around axons in the nervous system. The term refers to the development and maturation of insulating layers that wrap the nerve fiber to improve signal transmission.

In the central nervous system, oligodendrocytes extend their membranes to enwrap segments of several different axons, creating internodes separated by nodes of Ranvier. In the peripheral nervous system, Schwann cells wrap a single axon segment to form the myelin sheath, also with nodes of Ranvier between segments. The myelin sheath is a lipid-rich membrane that acts as insulation, reducing ionic leakage and increasing the speed of electrical conduction along the axon.

The main functional benefit of myelination is faster nerve signal transmission, achieved through saltatory conduction, where impulses jump between nodes rather than traveling along every millimeter of axon. Myelination also lowers the metabolic cost of signaling by reducing the need for widespread ion pumping across the membrane.

Development and regulation of myelination vary by region and species. In humans, myelination begins prenatally and continues after birth, with different brain areas myelinating at different times. Signals such as neuregulins, thyroid hormones, and activity-dependent cues influence myelination, and glial-axon interactions help determine sheath thickness and length.

Demyelinating diseases disrupt conduction and can cause sensory, motor, or cognitive deficits. Multiple sclerosis is a common central nervous system disorder characterized by loss of myelin, while peripheral neuropathies involve Schwann cell–derived myelin loss. Remyelination can occur but may be incomplete or fail over time.