What forms the myelin sheath that covers many CNS axons?

The myelin sheath that covers many central nervous system (CNS) axons is formed by oligodendrocytes. These specialized glial cells extend their membranes around multiple axons, creating segments of myelin that insulate the axonal fibers. Myelination is crucial because it enhances the speed and efficiency of electrical signal transmission along the axon, a process known as saltatory conduction, where action potentials jump from one node of Ranvier to the next between myelinated segments. This is essential for proper functioning of the nervous system and plays a significant role in cognitive and motor functions.

In contrast, Schwann cells are responsible for myelinating axons in the peripheral nervous system (PNS), while astrocytes serve various functions including supporting neuronal metabolism and maintaining the blood-brain barrier. Microglia act as the resident immune cells in the CNS, involved in immune responses and clearing debris. Therefore, oligodendrocytes specifically cater to the myelination needs within the CNS, making their role in forming the myelin sheath distinctive and critical.