Clinical meaning
Multiple sclerosis (MS) is a chronic autoimmune inflammatory disease of the central nervous system in which the immune system attacks the myelin sheath that insulates nerve fibers (axons) in the brain and spinal cord. Understanding the demyelination process explains the wide variety of neurological symptoms, the relapsing-remitting pattern of the disease, and why symptoms can differ so dramatically between patients. In a healthy nervous system, oligodendrocytes produce myelin, a fatty insulating layer that wraps around axons in the CNS. Myelin enables rapid saltatory conduction of electrical impulses by allowing signals to jump between gaps in the myelin called nodes of Ranvier. This allows nerve impulses to travel at speeds up to 120 meters per second. Without myelin, conduction slows dramatically or fails completely. In MS, autoreactive T-lymphocytes cross the blood-brain barrier and attack myelin as if it were foreign. This triggers an inflammatory cascade involving macrophages, B-cells, and inflammatory cytokines that strips myelin from axons, forming characteristic lesions called plaques or scleroses. During acute inflammation, symptoms appear (a relapse or exacerbation). When inflammation subsides, partial remyelination can occur (a remission),...