Myelin

Myelin is a fatty substance that surrounds the axon of some nerve cells, forming an electrically insulating layer. It is essential for the proper functioning of the nervous system. It is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination or myelinogenesis.

Structure

Myelin is composed of about 40% water; the dry mass is about 70–85% lipids and about 15–30% proteins. Some of the proteins that make up myelin are Myelin basic protein (MBP), Myelin oligodendrocyte glycoprotein (MOG), and Proteolipid protein (PLP). The most important lipids of myelin are cholesterol, phospholipids, and galactocerebrosides.

Function

The main role of a myelin layer (or sheath) is to increase 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 saltatory conduction".

Clinical significance

Demyelination is the loss of the myelin sheath insulating the nerves, and is the hallmark of some neurodegenerative autoimmune diseases, including multiple sclerosis and acute disseminated encephalomyelitis.

See also

• Neuron
• Nervous system
• Neuroscience

References

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Myelin

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  Myelinated neuron

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  Myelin sheath

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  Saltatory conduction