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Myelin is a fatty substance that forms a protective sheath around nerve fibers in the central nervous system, including the brain and spinal cord. This sheath is crucial for the efficient transmission of electrical signals, or action potentials, along the length of the nerve fibers. Myelin is composed of lipids, proteins, and other molecules that work together to insulate and support the nerve fibers.

The process of myelination involves the wrapping of myelin around the axon, the long, slender projection of a neuron that conducts electrical impulses away from the cell body. This wrapping is typically performed by a type of glial cell called oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. Myelination occurs during development and can also be induced in adulthood under certain conditions.

The structure of myelin is characterized by alternating layers of lipid-rich and lipid-poor regions. The lipid-rich regions, known as the compact myelin, are composed primarily of lipids, while the lipid-poor regions, known as the paranodal junction, contain proteins that facilitate the transmission of electrical signals. This alternating structure allows for saltatory conduction, a mechanism where action potentials "jump" from one node of Ranvier to the next, significantly increasing the speed of signal transmission.

Myelin is essential for the proper functioning of the nervous system. It plays a critical role in various neurological processes, including sensory perception, motor control, and cognitive functions. Dysfunction or loss of myelin, as seen in conditions such as multiple sclerosis, can lead to impaired nerve conduction and a range of neurological symptoms.

In summary, myelin is a vital component of the nervous system that provides insulation and support for nerve fibers, facilitating the efficient transmission of electrical signals. Its structure and function are crucial for the normal operation of the central and peripheral nervous systems.