Which cells wrap around the axon to form the insulating myelin sheath?

The correct answer is Schwann Cells, as they are responsible for wrapping around the axons of peripheral neurons to create the myelin sheath. Myelin is a fatty substance that insulates the axons and enhances the speed of electrical impulses, allowing for efficient communication between neurons. Each Schwann cell forms one segment of the myelin sheath and provides not only insulation but also support for the regrowth of peripheral nerves following injury.

Oligodendrocytes, while similar in function, are found in the central nervous system; they create the myelin sheath for multiple axons, unlike Schwann cells which myelinate a single axon in the peripheral nervous system. Astrocytes play a supportive role in the brain and spinal cord, maintaining the blood-brain barrier and providing nutrients but are not involved in myelination. Microglia act as the immune cells of the central nervous system, responsible for cleaning up debris and responding to injury or disease, but they also do not contribute to the formation of the myelin sheath.