Final answer:
Multiple sclerosis is an autoimmune disease characterized by the breakdown of the myelin sheath surrounding nerve fibers in the central nervous system, leading to disrupted nerve signal transmission and various neurological symptoms.
Step-by-step explanation:
The correct answer to which of the following describes multiple sclerosis (MS) is A. A breakdown of the myelin sheath. MS is an autoimmune disorder that affects the central nervous system, particularly the brain and spinal cord. In MS, the immune system mistakenly attacks the myelin sheath, the protective covering that insulates nerve fibers. This deterioration disrupts the efficient transmission of electrical impulses along nerve cells and leads to the various symptoms associated with MS, such as muscle weakness, coordination issues, and sensory disturbances.
Symptoms of MS can range from mild to severe and may include visual disturbances, difficulty with coordination and balance, muscle weakness, and cognitive dysfunction. The progression of the disease varies among individuals, exhibiting episodes of symptoms that may resolve or may lead to gradual and irreversible decline. Although MS is chronic and presently incurable, certain treatments can help manage symptoms and modify the course of the disease.