What is the process by which myelination increases the speed of action potential conduction?

What is the process by which myelination increases the speed of action potential conduction?

• A. Saltatory conduction, where the action potential jumps between nodes of Ranvier
• B. Continuous conduction along unmyelinated axons
• C. Retrograde conduction back toward the soma
• D. Passive diffusion of ions along the axon

Answer: (A)

Myelination speeds up conduction through saltatory conduction. The myelin sheath insulates segments of the axon, leaving gaps called nodes of Ranvier where voltage-gated sodium channels are concentrated. This insulation increases membrane resistance and decreases membrane capacitance, so the depolarizing current travels quickly along the insulated internodes with little leakage. When the depolarization reaches a node, it triggers a new action potential, which then propagates to the next node. The signal thus jumps from node to node, skipping the myelinated stretches, which makes transmission much faster than along unmyelinated axons where the action potential must be regenerated continuously along every patch. Retrograde conduction toward the soma and passive diffusion of ions do not account for this rapid, node-to-node propagation.

Myelination speeds up conduction through saltatory conduction. The myelin sheath insulates segments of the axon, leaving gaps called nodes of Ranvier where voltage-gated sodium channels are concentrated. This insulation increases membrane resistance and decreases membrane capacitance, so the depolarizing current travels quickly along the insulated internodes with little leakage. When the depolarization reaches a node, it triggers a new action potential, which then propagates to the next node. The signal thus jumps from node to node, skipping the myelinated stretches, which makes transmission much faster than along unmyelinated axons where the action potential must be regenerated continuously along every patch. Retrograde conduction toward the soma and passive diffusion of ions do not account for this rapid, node-to-node propagation.