Information AboutMyelin |
| CATEGORIES ABOUT MYELIN | |
| nervous system | |
| neurons | |
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Myelin is an electrically insulating '''. COMPOSITION OF MYELIN Myelin made by different cell types varies in chemical composition and configuration, but performs the same insulating function. Myelinated neurons are white in appearance, hence the "white matter" of the brain. Myelin is composed of about 80% Lipid Fat and about 20% Protein . Some of the proteins that make up myelin are Myelin Basic Protein (MBP), Myelin Oligodendrocyte Glycoprotein (MOG) and Proteolipid Protein (PLP). Myelin is made up primarily of a Glycolipid called galactocerebroside. The intertwining of the hydrocarbon chains of sphingomyelin serve to strengthen the myelin sheath. FUNCTION OF MYELIN LAYER The main consequence of a myelin layer (or ''sheath'') is an increase in the speed at which Impulses propagate along the ''myelinated'' fiber. Along ''unmyelinated'' fibers, impulses move continuously as waves, but, in myelinated fibers, they hop or "propagate by Saltation ". Myelin increases resistance across the cell membrane by a factor of 5,000 and decreases capacitance by a factor of 50. Myelination also helps prevent the electrical current from leaving the axon. When a peripheral fiber is severed, the myelin sheath provides a track along which regrowth can occur. Unmyelinated fibers and myelinated axons of the mammalian central nervous system do not regenerate. DEMYELINATION AND DYSMYELINATION Demyelination is the act of demyelinating, or the loss of the myelin sheath insulating the nerves, and is the hallmark of some Neurodegenerative Autoimmune diseases, including Multiple Sclerosis , Transverse Myelitis , Chronic Inflammatory Demyelinating Polyneuropathy , Guillain-Barre Syndrome . When myelin degrades, conduction of signals along the nerve can be impaired or lost, and the nerve eventually withers. The . Heavy Metal poisoning may also lead to demyelination. Even very small amounts of Mercury have been shown to be particularly destructive to nerve sheaths. {Link without Title} University of Calgary: How Mercury Causes Brain Neuron Degeneration Research to repair damaged myelin sheaths is ongoing. Techniques include surgically implanting Oligodendrocyte Precursor Cell s in the central nervous system and inducing myelin repair with certain antibodies. While there have been some encouraging results in mice (via Stem Cell ) implant, it is still unknown whether this technique can be effective in humans. {Link without Title} FuturePundit January 20, 2004 Dysmyelination on the other hand is different from the lesions producing process of active demyelination and is characterized by defective structure and function of myelin sheaths. Such defective sheaths often arise from genetic mutations affecting the biosynthesis and formation of myelin. Examples of human diseases where dysmyelination has been implicated include leukodystrophies (Pelizaeus-Merzbacher disease, Canavan disease) and schizophrenia. Krämer-Albers at al., 2006 Matalon et al., 2006 Tkachev et al., 2007 SYMPTOMS OF DEMYELINATION Demyelination destruction or loss of the myelin sheath typically results in diverse symptoms. The symptoms are determined by the functions normally contributed by the affected neurons. Damage to the myelin sheath disrupts signals between the brain and other parts of the body producing a range of symptoms. Symptoms are often Heterogeneous — dependent on Pathophysiology of demyelination — differing from patient to patient, and have different presentations upon clinical observation and in laboratory studies.
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