Final answer:
The oligodendrocyte (option A) is the glial cell type that forms the myelin sheath in the CNS, insulating multiple axons, unlike Schwann cells in the PNS which only insulate one axon segment.
Step-by-step explanation:
The type of glial cell that forms the myelin sheath in the central nervous system (CNS) is the oligodendrocyte. Oligodendrocytes have a few processes that extend from the cell body, each reaching out to insulate axons with a myelin sheath. Unlike Schwann cells in the peripheral nervous system (PNS), which insulate only one axon segment, an oligodendrocyte can provide myelin for multiple axon segments, either for the same axon or for different axons.
In summary, the CNS contains several types of glial cells including oligodendrocytes, the myelin-forming cells, as well as astrocytes, microglia, and ependymal cells, each with their distinct functions supporting neurons. Astrocytes maintain the chemical environment, microglia act as phagocytes in immune surveillance, and ependymal cells produce cerebrospinal fluid for cushioning neurons.