USA Biology Olympiad (USABO) Practice Exam

What cell myelinates the axon in the peripheral nervous system?

1. Oligodendrocyte

2. Astrocyte

3. Schwann cell

4. Microglia

The correct answer is: Schwann cell

In the peripheral nervous system (PNS), Schwann cells are responsible for the myelination of axons. Myelination is a process that involves wrapping the axon with a protective sheath made of myelin, which is essential for the efficient conduction of electrical impulses along the nerve fibers. Schwann cells create this myelin sheath by surrounding individual axons, providing not only insulation but also facilitating the rapid transmission of action potentials through a process called saltatory conduction. Other cell types mentioned serve different functions within the nervous system. Oligodendrocytes, for example, are the myelinating cells in the central nervous system (CNS), where they can myelinate multiple axons at once, unlike Schwann cells, which typically myelinate a single axon. Astrocytes play a crucial role in maintaining the blood-brain barrier and providing metabolic support to neurons, while microglia act as the immune cells of the CNS, involved in responding to injury and disease. Thus, Schwann cells are uniquely adapted for myelination in the peripheral nervous system, making them the correct answer.