Myelin sheath is a fatty product formed from specific neuroglial cells that provides numerous vital supporting functions as well as increases the rate of conduction of action potentials for some central and peripheral nervous system neurons. An axon wrapped in myelin sheath is said to be myelinated fibers, as such, axons not wrapped in myelin are non-myelinated fibers. In the central nervous system, the myelinated fibers have the collective name of white matter, and the nonmyelinated fibers are collectively known as gray matter as they look white and gray respectively on gross inspection of the brain in sagittal cross-section. Myelin is formed via oligodendrocytes and Schwann cells in the central and peripheral nervous systems respectively. Many physiologic complications and clinical symptoms can arise from the malformation and destruction of myelin.
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