What is the primary functional effect of myelin on nerve fibers?

• A. Reduces conduction velocity
• B. Increases speed and efficiency of signal transmission
• C. Increases energy consumption
• D. Blocks ion flow

Answer: (B)

Myelin increases the speed and efficiency of electrical signaling along axons. It wraps the axon as an insulating sheath, which raises the membrane’s resistance and lowers its capacitance. This keeps the depolarizing current from leaking away, allowing the signal to travel quickly to the next exposed region. The action potential is then regenerated at the nodes of Ranvier, so the electrical impulse “jumps” from node to node in a process called saltatory conduction. This arrangement dramatically speeds conduction and reduces energy use, since fewer ions cross the membrane and fewer pumps must restore ion balances over time. In the central nervous system, oligodendrocytes provide this myelin, while in the peripheral nervous system, Schwann cells do. Myelin does not slow conduction, it does not increase energy consumption, and it does not block ion flow; ions still flow at the nodes to sustain propagation.