Final answer:
Astrocytes are the glial cells that form the blood-brain barrier, regulating molecule passage to protect the CNS.
Step-by-step explanation:
Among the glial cells found in the central nervous system (CNS), astrocytes are the particular type that are part of the blood-brain barrier (BBB). Astrocytes assist in maintaining the chemical environment needed for neuron function and are vital for the regulation of the BBB, which is a membrane that separates the brain's circulatory system from the surrounding tissue, helping to protect the CNS from potential toxins and regulate the passage of molecules.
While other glial cells, such as oligodendrocytes, are involved in the formation of the myelin sheath, and microglia serve as phagocytes engaged in immune surveillance, it is the astrocytes that have the unique role of forming the BBB. Thus, the correct answer to which glial cells are part of the blood-brain barrier is astrocytes.