Myelin Sheath
Definition
- A white, fatty substance that insulates and protects the axon for some neurons.

Facts
- The Myelin Sheath speeds the transmission of impulses.
- The Myelin Sheath is wrapped around the axon to protect it.
- The myelin sheath of the central (and sometimes peripheral) nervous system bears the brunt of pathologic process while other neural structures are relatively spared.
- Discovered by the German Pathologist Rudolph Virchow in 1854


external image schwann_myelin.jpg


Anatomy of the Myelin Sheath
Schwann Cell - surround the axons that is being covered by the Myelin Sheath
Axon - Axon is what the Myelin Sheath is protecting. It is a long threadlike part of a nerve cell which impulses are conducted from the cell.
Nodes of Ranvier - a gap in between the Myelin Sheath of a nerve, but between adjacent Schwann Cells.

Disorders
- Dysmyelinatin – Profound disturbance in the formation and preservation of myelin so that its proper functioning is never established. These disorders are also termed leukodystrophies, and almost all of them manifest themselves early in life and are genetically determined.
- Demyelinating – the Myelin Sheath, once properly formed and functioning, is destroyed by a disease process. Examples include, central pontine myelinolysis, progressive mulifocal leukoencephalopaty, and subacute combined degeneration of the spinal cord
- Krabbes Disease – usually appears in early years of life, die after one to two years.
- Multiple Sclerosis - destroys the Myelin Sheath causing peoples behavior to become erratic and uncoordinated
-Schilder's Disease - Schilder's disease is not the same as Addison-Schilder disease (adrenoleukodystrophy). Schilder's disease is a rare progressive demyelinating disorder which usually begins in childhood
-Other disorders include Leukodystrophy, Centreal Pontine Myelinolysis, Progressive Multifocal Leukoencephalopathy, Metachromatic Leukodystrophy, Alexander’s disease, Gamma Globulin, Obligoclonal Bands, Perivenous Encephalomyelitis, Post Vaccinal, Post Infectious, Experimental Allergic Encephalomyelitis

References
http://www.britannica.com/EBchecked/topic/400357/myelin-sheath
http://www.uvm.edu/~jkessler/NP/neumyshe.htm

Books
Understanding Psychology ~ Glencoe by Richard A. Kasschau