Myelin sheath composition refers to the unique, highly specialized molecular makeup of the multi-layered lipid and protein structure that insulates the axons of many neurons, allowing for rapid and efficient transmission of electrical impulses. This composition is characterized by an exceptionally high lipid-to-protein ratio, with cholesterol, galactolipids (like galactocerebroside), and sphingomyelin being the dominant lipid species. The integrity of this composition is crucial for nervous system function and is a major determinant of neurological health.
Origin
This term is a core concept in neurobiology, defining the structural basis of nerve impulse conduction. The ‘myelin sheath’ itself is named after the Greek word myelos, meaning ‘marrow.’ Its composition is a direct reflection of the specialized function of oligodendrocytes and Schwann cells. In the hormonal context, the synthesis and maintenance of this lipid-rich structure are profoundly influenced by thyroid hormones and sex steroids.
Mechanism
The high lipid content of the myelin sheath, approximately 70-85% of its dry weight, is responsible for its insulating properties, which drastically increase the speed of action potential propagation via saltatory conduction. Cholesterol provides rigidity and stability, while galactolipids are unique to the myelin structure and essential for its formation and maintenance. Hormones regulate the gene expression of the key enzymes involved in the synthesis of these specific lipids and myelin proteins, ensuring the precise and dynamic assembly of this critical structure throughout development and adulthood.
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