Myelin
From Freepedia
In neuroscience, myelin is an electrically insulating fatty layer that surrounds the axons of many neurons, especially those in the peripheral nervous system. It is an outgrowth of glial cells: Schwann cells supply the myelin for peripheral neurons while oligodendrocytes supply it to those of the Central nervous system. The myelin produced by the different cell types varies in its chemical composition or configuration, but performs the same function. Myelinated neurons are white in appearance, hence the well known "white matter" of the brain. Myelin is made up primarily of a sphingolipid called sphingomyelin, and it is thought that the intertwining of the hydrocarbon chains of sphingomyelin serves to strengthen the myelin sheath.
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"). Myelination also helps prevent the electrical current from leaving the axon and causing a short circuit in the brain. 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 sytsem do not regenerate.
Demyelination is a loss of myelin and is the root cause of symptoms experienced by patients with diseases such as multiple sclerosis and transverse myelitis. The immune system may play a role in demyelination associated with such diseases. Heavy metal poisoning may also lead to demyelination. When an axon's myelin degrades due to these diseases, conduction can be impaired or lost.
Research is currently being undertaken to repair damaged myelin sheaths. These techniques include surgically implanting oligodendrocytes in the central nervous system and inducing myelin repair with certain antibodies. However, whether or not these strategies can lead to a cure for patients suffering from multiple sclerosis is very speculative.
External links
- Athabasca University Biological Psychology Website
- The MS Information Sourcebook, Myelin
- The Myelin Repair Foundation
- H & E Histology
- Luxol Fast Blue: Modified Kluver's Method to stain for Myelin Sheath
