Which structure insulates the axon to speed conduction?

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

Answer: (D)

Insulating the axon increases conduction speed. The insulation comes in the form of the myelin sheath, a fatty wrapping produced by glial cells (Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system). This sheath wraps the axon in segments and leaves gaps called nodes of Ranvier. Because myelin reduces current leakage and raises membrane resistance while lowering membrane capacitance, the electrical signal travels much faster by jumping from node to node—a process known as saltatory conduction. The soma and dendrites aren’t involved in speeding conduction along the axon, and the axon itself is the conducting fiber, not the insulation. Without myelin, conduction would be slower; with it, signals move quickly across long distances.