Multiple Sclerosis is a chronic disease of the central nervous system in which myelin is destroyed.

• A. Neurons destroyed
• B. Dendrites destroyed
• C. Synapses destroyed
• D. Myelin is destroyed

Answer: (D)

The main idea here is that multiple sclerosis involves destruction of the myelin sheath in the central nervous system, not the nerve cells themselves. Myelin wraps around axons and allows electrical signals to jump quickly from node to node, a process called saltatory conduction. When the myelin is damaged in MS, these signals slow down or stop, leading to the neurological symptoms people experience. This is due to an autoimmune attack on CNS myelin produced by oligodendrocytes.

If neurons were destroyed, or dendrites or synapses were primarily damaged, the pattern of problems and the underlying disease mechanism would be different. MS is characterized by demyelination, so stating that myelin is destroyed best matches the disease.