A protective, insulating layer of lipoprotein material that encases the axons of many neurons in the central and peripheral nervous systems. Produced by glial cells, this sheath significantly increases the speed and efficiency of electrical impulse conduction along the nerve fiber. The integrity of the myelin sheath is crucial for rapid and coordinated communication between different regions of the brain and body.
Origin
The term is derived from the Greek myelos, meaning “marrow” or “pith,” referring to the substance’s soft, inner nature, combined with ‘sheath’ for its covering function. The structure was first described microscopically in the 19th century, with its physiological function in saltatory conduction elucidated later. Hormonal influences on its formation and maintenance highlight the intricate link between endocrinology and neurobiology.
Mechanism
Myelin acts as an electrical insulator, forcing the action potential to “jump” between the Nodes of Ranvier, a process termed saltatory conduction, which dramatically accelerates signal transmission. Hormones, particularly thyroid hormones and certain sex steroids, are essential for the proper development and maintenance of the myelin-producing cells, oligodendrocytes and Schwann cells. Hormonal dysregulation can therefore compromise the structural integrity and function of the central nervous system.
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