The myelin sheath serves to insulate around some axons to speed impulses.

• A. Produce neurotransmitters
• B. Insulate around axons to speed impulses
• C. Store nutrients
• D. Remove waste

Answer: (B)

Insulating axons to speed impulse conduction is what the myelin sheath does. By wrapping around many axons, myelin creates a high resistance layer that reduces current leakage and allows electrical signals to jump from one node of Ranvier to the next. This saltatory conduction makes nerve impulses travel much faster than they would along unmyelinated fibers. In the nervous system, Schwann cells form myelin in the peripheral nerves and oligodendrocytes do so in the central nervous system.

Other roles listed don’t fit myelin: neurotransmitters are produced at synapses, not by the myelin sheath; nutrient storage isn’t a function of myelin; waste removal is handled by other glial cells and cellular processes, not by the myelin sheath itself.