What characterizes MS?

• A. Slowed or blocked action potential conduction
• B. Loss of saltatory conduction
• C. Increased ion leakage along axons
• D. Impaired communication between neurons

Answer: (A)

Multiple sclerosis is a demyelinating disease of the central nervous system. Myelin normally speeds nerve impulses by enabling saltatory conduction, where signals jump between nodes of Ranvier. When myelin is damaged, insulation is lost, which raises membrane resistance and capacitance at the affected stretches and disrupts the rapid, jump-like propagation. The result is that action potential conduction becomes slower and can even be blocked in demyelinated segments. So, the defining functional change is slowed or blocked conduction along affected axons. (Loss of saltatory conduction is a consequence of demyelination, and broader impaired neural communication can occur, but the clearest signature is the slowed or blocked conduction.)