Which statement best contrasts CNS oligodendrocyte myelination with PNS Schwann cell myelination?

• A. CNS glial cells in the brain are unmyelinating overall.
• B. PNS Schwann cells myelinate axons in the brain only.
• C. Oligodendrocytes myelinate a single axon in the CNS.
• D. In the CNS, oligodendrocytes myelinate multiple axons; in the PNS, Schwann cells myelinate a single axon.

Answer: (D)

The main idea is how myelin is produced and organized by glial cells in the CNS versus the PNS. Oligodendrocytes in the CNS extend their processes to wrap myelin around multiple axons, so a single oligodendrocyte can contribute myelin sheaths to several different axons. In contrast, Schwann cells in the PNS each form a myelin sheath around a single axon segment, meaning one Schwann cell myelinates only one axon (for that segment), while many Schwann cells line the same axon to cover its length. Therefore, describing the CNS as having oligodendrocytes that myelinate multiple axons and the PNS as having Schwann cells that myelinate a single axon correctly contrasts their typical organization.