Which statement about myelin and conduction velocity is correct?

• A. It equally distributes ion channels along the entire axon surface.
• B. It eliminates the need for voltage-gated channels.
• C. It increases conduction velocity by enabling saltatory conduction between nodes of Ranvier.
• D. It blocks synaptic transmission at the axon terminals.

Answer: (C)

Myelin increases conduction velocity by enabling saltatory conduction between nodes of Ranvier. The insulating myelin sheath wraps the axon and reduces leak of current across the membrane, which lowers membrane capacitance and increases membrane resistance. Because of this, the depolarizing current travels quickly inside the myelinated segments and only needs to be reactivated at the nodes, where voltage-gated Na+ channels are concentrated. At each node, the signal is regenerated, so the impulse effectively "hops" from node to node, dramatically speeding up transmission compared with unmyelinated fibers. Thicker myelin and larger axon diameter both boost speed, while the channels are not spread evenly along the entire surface—channels cluster at the nodes. Myelin does not eliminate voltage-gated channels, nor does it block synaptic transmission at terminals.