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An Overview
Multiple Sclerosis is a chronic disease of the central nervous system (CNS), which consists of the brain and the spinal cord. Multiple Sclerosis refers to the numerous areas of patchy scarring, or plaques, that result from Demyelination. Demyelination is the destruction of the myelin sheath, a fatty insulation that covers most nerve fibers. Myelin is made of cell membranes that are produced by specialized cells called oligodendrocytes. Myelin coats lie in segments along the axons, long filaments that carry electric impulses away from the nerve cell. Nodes of Ranvier separate the myelin coat segments. In addition the nodes of Ranvier contain channels for sodium ions, which boost the electrical charge required to pass signals from one nerve to another. During multiple sclerosis when the myelin sheath is destroyed signals transmitted throughout the CNS are disrupted. The body tries to compensate for the myelin loss by increasing the density of the sodium channels within the nodes of Ranvier so electrical charges can continue to be carried, in spite of myelin loss. Unfortunately, multiple sclerosis outpaces this corrective action, and after demyelination, axon destruction occurs which results in the irreversibility of the disease.
Multiple Sclerosis is defined as a autoimmune disease, meaning that the body's immune system is damaged by either genetic or environmental factors, which results in the attacking of the body's own tissues. In the case of MS, these tissues are the myelin sheath that surrounds the nerve fibers in the brain.
The severity of MS is dependent on the location of the plaques within the CNS and the extent of the demyelination. Multiple sclerosis is usually grouped into four types: relapsing-remitting, primary-progressive, secondary-progressive, progressive-relapsing MS. The latter three forms generally fall into the category of chronic-progressive MS.
Relapsing-remitting multiple sclerosis usually occurs in younger patients and is the most common form of MS. Relapsing-remitting MS is classified by a symptom flare up for several days, that afterward go into remission for over four to eight weeks. Studies have shown that the symptoms during the flare up period are fairly mild for about half of the patients. In addition, the remission period may be spontaneous or induced by immunosuppressive drugs. Spontaneous remission probably occurs when demyelinated nerve cells are compensating by increasing the density of the sodium channels that carry electric charges. A person in remission may have subtle attacks however may not notice it, for example there may be a slight awkwardness in gait or coordination.
Chronic-progressive MS is used to describe cases where symptoms worsen and there is no remission. Studies show that chronic-progressive MS is due to the severing of nerve axons during the disease process. Chronic-Progressive MS leads to speech problems and paralysis, which usually goes downhill from there.
Please email questions or comments to: remckoy@davidson.edu
This web page is an assignment for the advanced neuroscience class at Davidson College. It should only be used for information purposes.