This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
[{'content': 'Saltatory conduction in myelinated axons results from the fact that \nSelect and explain. \nA. Salt concentration is increased beneath the myelin segments, B. Non gated ion channels are present beneath the segments of myelin, C. Membrane resistance is decreased beneath the segments of myelin, D. Voltage-gated sodium channels are concentrated at the nodes of Ranvier', 'role': 'user'}, {'content': 'Answer: D \nExplanation: "Saltatory" Conduction in Myelinated Fibers from Node to Node: Even though almost no ions can flow through the thick myelin sheaths of myelinated nerves, they can flow with ease through the nodes of Ranvier.Therefore, action potentials occur only at the nodes. Yet the action potentials are conducted from node to node, this is called saltatory conduction.That is, electrical current flows through the surrounding extracellular fluid outside the myelin sheath, as well as through the axoplasm inside the axon from node to node, exciting successive nodes one after another. Thus, the nerve impulse jumps along the fiber, which is the origin of the term "saltatory."Ref: Guyton; 13th edition; Chapter 5; Membrane Potentials and Action Potentials', 'role': 'assistant'}]