Nodes of Ranvier contribute to conduction by which description?

• A. Gaps in the myelin sheath where ions exchange to boost conduction
• B. Regions where neurotransmitters are released
• C. Areas of myelination by Schwann cells
• D. The site of axon hillock

Answer: (A)

Nodes of Ranvier are gaps in the myelin sheath along a myelinated axon where voltage-gated sodium and potassium channels are concentrated. This setup lets the action potential be regenerated at each node: when the signal reaches a node, sodium channels open, Na+ ions rush in, and the membrane depolarizes again. Because the myelin elsewhere reduces leakage and lowers the membrane capacitance, the depolarizing current can travel quickly to the next node, producing saltatory conduction. This is why these gaps boost conduction efficiency and speed.

The other options don’t fit because neurotransmitter release occurs at synapses, not along the axon’s gaps; Schwann cells create the myelin segments themselves, not the gaps; and the axon hillock is the initial point where action potentials begin, not where they are reinitiated during propagation along the axon.