If the insulation around an axon (myelin) is damaged, what effect is most likely?

• A. Slower signal transmission
• B. Faster signal transmission
• C. More neurotransmitter production
• D. Increased neuron size

Answer: (A)

When a nerve fiber is myelinated, the insulation and the gaps at the nodes of Ranvier let the electrical signal hop quickly from node to node, a process called saltatory conduction. This arrangement increases conduction velocity and reduces the energy needed to reset ion concentrations after each impulse. If the myelin sheath is damaged, the insulating effect is lost and current leaks across the membrane between nodes. The signal has to travel more slowly and may even fail to propagate reliably, so transmission becomes much slower and less efficient. Neurotransmitter production happens at synapses, not along the length of the axon, and isn’t directly increased by healthy myelin; similarly, neuron size isn’t determined by myelin status in this context. Therefore, the most likely outcome of damaged myelin is slower signal transmission.