What is the function of the myelin sheath?

• A. It stores minerals.
• B. It produces bile.
• C. It regulates hormones.
• D. It speeds up electrical conduction along the nerve.

Answer: (D)

Myelin sheaths wrap around axons to insulate electrical signals, which speeds up how quickly a nerve impulse travels. This insulation increases membrane resistance and decreases membrane capacitance, so the impulse can travel rapidly from one gap in the myelin (the node of Ranvier) to the next. This jump between nodes, called saltatory conduction, makes conduction much faster than if the axon were unmyelinated. Glial cells create this insulation: oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. The other described functions—storing minerals, producing bile, and regulating hormones—are carried out by bones, the liver/gallbladder, and endocrine glands, not by the myelin sheath.