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Overview of Demyelinating Disorders

By

Michael C. Levin

, MD, College of Medicine, University of Saskatchewan

Last full review/revision Mar 2021
CLICK HERE FOR THE PROFESSONAL VERSION
Topic Resources

Most nerve fibers 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. Much like the insulation around an electrical wire, the myelin sheath enables nerve signals (electrical impulses) to be conducted along the nerve fiber with speed and accuracy. When the myelin sheath is damaged, nerves do not conduct electrical impulses normally. Sometimes the nerve fibers are also damaged.

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 fiber can die. Nerve fibers in the central nervous system (brain and spinal cord) cannot fully regenerate themselves. Thus, these nerve cells are permanently damaged.

Insulating a Nerve Fiber

Most nerve fibers 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. Much like the insulation around an electrical wire, the myelin sheath enables nerve signals (electrical impulses) to be conducted along the nerve fiber with speed and accuracy. When the myelin sheath is damaged (called demyelination), nerves do not conduct electrical impulses normally.

Insulating a Nerve Fiber

Did You Know...

  • Nerves are covered with tissues that, much like insulation around an electric wire, help the nerve conduct impulses.

Causes of Demyelinating Disorders

When babies are born, many of their nerves lack mature myelin sheaths. As a result, their movements are jerky, uncoordinated, and awkward. As myelin sheaths develop, movements become smoother, more purposeful, and more coordinated.

In adults, the myelin sheath can be damaged or destroyed by the following:

Such destruction is called demyelination.

Some disorders that cause demyelination have no known cause. These disorders are called primary demyelinating disorders. The most common of these disorders is

Other primary demyelinating disorders include

Sometimes primary demyelinating disorders develop after a viral infection or vaccination against a viral infection. A likely explanation is that the virus or another substance somehow triggers the immune system to attack the body’s own tissues (autoimmune reaction Autoimmune Disorders An autoimmune disorder is a malfunction of the body's immune system that causes the body to attack its own tissues. What triggers autoimmune disorders is not known. Symptoms vary depending on... read more ). The autoimmune reaction results in inflammation, which damages the myelin sheath and the nerve fiber under it.

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Bell Palsy
Bell palsy is sudden weakness or paralysis of the muscles on one side of the face due to malfunction of the seventh cranial nerve. This nerve moves facial muscles, stimulates salivary and tear glands, detects tastes, and controls a muscle involved in hearing. Which of the following is often the first symptom of Bell palsy?
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