What is Myelin?

Most nerve fibres inside and outside the brain are wrapped with many layers of tissue composed of a fat (lipoprotein) called myelin.

These layers form the myelin sheath. Like the insulation around an electrical wire, the myelin sheath enables electrical impulses to be conducted along the nerve fibre with speed and accuracy. When the myelin sheath is damaged, nerves do not conduct impulses normally.

In adults, the myelin sheath can be destroyed by stroke, inflammation, immune disorders, metabolic disorders and nutritional deficiencies (for example, a lack of vitamin B12). Such destruction is called demyelination. Poisons, drugs (such as the antibiotic ethambutol) and excessive use of alcohol can damage or destroy the myelin sheath. If the sheath is able to repair and regenerate itself, normal nerve function may return.

However, if the sheath is severely damaged, the underlying nerve fibre can die causing irreversible damage. Generally nerve fibres cannot regenerate themselves.

Disorders that cause demyelination in the central nervous system (the brain and spinal cord) and have no known cause are called primary demyelinating disorders. Multiple sclerosis is the most common of these disorders.

The term "multiple sclerosis" refers to the many areas of scarring (sclerosis) that result from demyelination of nerves.

Amended April 2008