[Campbell Biology P.1125] Based on the provided text and Figure 48.14, which statement about ... | Practice Question
Based on the provided text and Figure 48.14, which statement about myelin sheaths and Nodes of Ranvier is correct?
A: Myelin sheaths are formed by neurons themselves and are primarily composed of protein, facilitating continuous action potential propagation along the entire axon.
B: Nodes of Ranvier are regions where the myelin sheath is absent, and voltage-gated sodium channels are concentrated, allowing action potentials to "jump" from node to node.
C: In the PNS, oligodendrocytes are responsible for forming the myelin sheath, while Schwann cells myelinate axons in the CNS.
D: The TEM image in Figure 48.14 shows that the myelin sheath is a single layer of membrane that tightly adheres to the axon without any gaps.
Explanation
Nodes of Ranvier are critical for saltatory conduction because they are the only points where voltage-gated sodium channels are abundant and action potentials can be regenerated, allowing the signal to jump along the axon, as described in the text and illustrated in the figure.