Question at position 22 Which statement best explains why myelination increases the velocity of nerve impulse transmission?Myelin prevents ion exchange along the entire axon membrane.Myelin converts electrical signals into chemical signals along the axon.Myelin allows action potentials to propagate through saltatory conduction between nodes of Ranvier.Which statement best explains why myelination increases the velocity of nerve impulse transmission?Clear my selection

Question

BlackTom AI · Accepted Answer

Myelination enables saltatory conduction, allowing action potentials to “jump” between nodes of Ranvier and thereby travel much faster along an axon.

1. Relevant knowledge points and concepts
- Neurons propagate action potentials (APs) via ion fluxes across the membrane (Na+ influx for depolarization, K+ efflux for repolarization).
- Myelin is a multilayered lipid sheath produced by Schwann cells (PNS) or oligodendrocytes (CNS) that covers internodal regions of the axon.
- Nodes of Ranvier are small gaps between myelinated segments rich in voltage-gated Na+ and K+ channels.
- Saltatory conduction: APs are regenerated only at nodes and passively spread under the myelin between nodes.

2. Step-by-step reasoning
- Under myelin, membrane capacitance is reduced and membrane resistance is increased. Reduced capacitance means less charge is required to change membrane potential; increased resistance reduces current leak.
- When an AP at one node depolarizes the membrane, current flows rapidly through the low-capacitance internode to the next node.
- At the next node, sufficient depolarization opens voltage-gated Na+ channels, regenerating a full AP there. The signal thus “jumps” node-to-node instead of being continuously regenerated along the whole membrane.

3. Calculations / intermediate steps
- No numerical calculation is required, but conceptually: lower capacitance (C) reduces the time constant τ = Rm·C, so τ decreases and membrane potential can change faster; higher membrane resistance (Rm) preserves current over distance (length constant increases), enabling effective passive spread to the next node.

4. Why the correct answer is correct
- The statement “Myelin allows action potentials to propagate through saltatory conduction between nodes of Ranvier” directly describes the biophysical mechanism that increases conduction velocity by limiting AP regeneration to nodes and enabling fast passive spread across internodes.

5. Why other options are incorrect
- “Myelin prevents ion exchange along the entire axon membrane.” Incorrect: myelin prevents ion exchange only at internodes, not at nodes; ion exchange still occurs at nodes where APs are regenerated.
- “Myelin converts electrical signals into chemical signals along the axon.” Incorrect: myelin does not convert modalities; electrical signaling remains electrical along the axon; chemical transmission occurs at synapses, not along the axon.
- The fourth option is a repeat/question formatting artifact and not a valid explanation.

6. Conclusion
Therefore, the correct answer is: Myelin allows action potentials to propagate through saltatory conduction between nodes of Ranvier. This matches the provided answer.

类似问题

Rapid conduction of action potentials around the nervous system is achieved in several ways, including:

When an axon is myelinated, one of the consequences is the redistribution of:

Which of the following statements with regards to myelinated and unmyelinated axons is CORRECT? (1 mark)

What is the primary function of the nodes of Ranvier in a myelinated neuron?

The Myelin sheath;

In __________ conduction, the impulse jumps from node of Ranvier to node of Ranvier.

In __________ conduction, the impulse jumps from node of Ranvier to node of Ranvier.

In a myelinated axon, the action potential _____ the segments of myelin, going from one node of Ranvier to the next.

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