Which structure coats and insulates the axon to speed neural transmission?

• A. Myelin
• B. Soma
• C. Axon Terminal
• D. Dendrite

Answer: (A)

Conduction speed along the axon is increased by a myelin sheath. Myelin coats the axon and acts as insulation, produced by glial cells (oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system). This insulation reduces leakage of electrical current and raises membrane resistance while lowering capacitance, so the nerve impulse can travel faster. In myelinated fibers, signals jump from one gap called a node of Ranvier to the next, a process known as saltatory conduction, which speeds transmission dramatically. The other structures—soma, axon terminal, and dendrites—have different roles in neuron function and do not provide this insulating, speed-enhancing sheath.