What fatty substance surrounds the axon and increases the speed at which signals travel?

• A. Myelin
• B. Nerves
• C. Dendrites
• D. Synapse

Answer: (A)

The main idea here is that the myelin sheath acts as insulation around the axon, speeding up how quickly a nerve signal travels. Myelin is a fatty layer produced by glial cells (Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system). This insulation increases electrical resistance across the axon membrane and reduces the area that must be depolarized, so the electrical signal doesn’t leak away. Because signals jump from one gap, called a node of Ranvier, to the next, the conduction velocity increases dramatically—a process known as saltatory conduction. If there were no myelin, the impulse would have to travel along every inch of the membrane, which is much slower. The other terms describe different parts or features: nerves are bundles of many neurons; dendrites are the receiving branches of a neuron; and a synapse is the junction where a signal passes from one neuron to another or to a muscle/gland.