Final answer:
Schwann cells are NOT associated with the CNS as they myelinate axons in the PNS, unlike oligodendrocytes, astrocytes, and microglia which are found in the CNS.
Step-by-step explanation:
Among the glial cells listed - microglia, astrocytes, Schwann cells, and oligodendrocytes - Schwann cells are the ones that are NOT associated with the central nervous system (CNS). Schwann cells are responsible for myelination in the peripheral nervous system (PNS), whereas oligodendrocytes perform a similar role within the CNS. Astrocytes support neurons in the CNS by maintaining the chemical environment around the neuron and are crucial for regulating the blood-brain barrier. Microglia act as phagocytes in the CNS, playing a key role in immune surveillance and protecting the nervous system.