Which feature insulates some axons to speed up transmission?

Which feature insulates some axons to speed up transmission?

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

Answer: (A)

The speed at which a nerve impulse travels along an axon is greatly increased when the axon is insulated by a myelin sheath. This fatty coating is produced by glial cells (oligodendrocytes in the CNS and Schwann cells in the PNS) and wraps around the axon with small gaps called nodes of Ranvier. The insulation raises membrane resistance and lowers membrane capacitance, so the electrical current travels more efficiently and leaks less across the membrane. As a result, the action potential can skip rapidly from one node to the next, a process known as saltatory conduction, which speeds up transmission dramatically compared to continuous conduction along an unmyelinated axon. The other structures—dendrites, soma, and neurotransmitters—play different roles (receiving signals, processing cell body functions, and chemical signaling at synapses), but they do not provide this rapid, insulating mechanism.

The speed at which a nerve impulse travels along an axon is greatly increased when the axon is insulated by a myelin sheath. This fatty coating is produced by glial cells (oligodendrocytes in the CNS and Schwann cells in the PNS) and wraps around the axon with small gaps called nodes of Ranvier. The insulation raises membrane resistance and lowers membrane capacitance, so the electrical current travels more efficiently and leaks less across the membrane. As a result, the action potential can skip rapidly from one node to the next, a process known as saltatory conduction, which speeds up transmission dramatically compared to continuous conduction along an unmyelinated axon. The other structures—dendrites, soma, and neurotransmitters—play different roles (receiving signals, processing cell body functions, and chemical signaling at synapses), but they do not provide this rapid, insulating mechanism.