Demyelination involves loss of the myelin sheath provided by Schwann cells, resulting in reduced or disorganized propagation of action potentials. This primarily causes:

• A. Increased conduction velocity
• B. No change in conduction
• C. Increased synaptic efficiency
• D. Reduced or disorganized propagation of action potentials

Answer: (D)

Demyelination removes the insulating layer around axons that normally supports fast, efficient saltatory conduction. Without myelin, the axonal membrane has higher capacitance and lower resistance, so current leaks across the membrane and the depolarization needed to trigger the next node of Ranvier arrives more slowly or may not reach threshold at all. This slows transmission and can lead to disorganized or blocked propagation of action potentials. So the primary effect is reduced or disorganized propagation of action potentials, not faster conduction, no change, or enhanced synaptic efficiency.