What is the gap between myelin sheath segments along an axon called?

• A. Axon
• B. Node of Ranvier
• C. Nucleus
• D. Neurilemma

Answer: (B)

The gap between myelin sheath segments along an axon is called the node of Ranvier. Myelin from glial cells insulates the axon, but at these gaps the membrane is exposed and rich in voltage-gated sodium channels. This lets the action potential be re-generated at each node, producing saltatory conduction where the nerve signal jumps from one node to the next, greatly speeding up transmission compared with unmyelinated fibers. The axon is the threadlike part of the neuron that carries impulses; the nucleus is the cell’s control center; the neurilemma is the outermost layer surrounding a peripheral nerve fiber formed by Schwann cells.