Multiple sclerosis — mechanism

• A. Inflammation of the brain
• B. Demyelination — gradual loss of the myelin sheath surrounding nerve cells
• C. Neuronal death
• D. Demyelination and remyelination cycles

Answer: (B)

MS is driven by an autoimmune attack on the myelin sheath that surrounds nerve fibers in the central nervous system. Myelin speeds nerve impulses, so when it’s damaged conduction becomes slow or blocked, producing the diverse neurological symptoms seen in MS. The formation of demyelinated patches, or plaques, explains why function can deteriorate over time and why attacks can come and go as inflammation flares.

Inflammation is part of the disease process, especially in acute lesions, but the key mechanism producing the symptoms is demyelination. Neuronal death can occur later or as a secondary consequence of prolonged conduction disruption, but it is not the primary process that defines MS. Remyelination can occur to some extent, but repair is often incomplete, leaving lasting deficits.