Final answer:
Astrocytes are essential for the formation and maintenance of the blood-brain barrier, providing both nutrients and protection to the brain by preventing harmful substances from entering.
Step-by-step explanation:
The type of glial cell that is necessary for the normal development of the blood-brain barrier is A. Astrocytes. Astrocytes make contact with both capillaries and neurons in the central nervous system (CNS).
They are essential not only for providing nutrients and regulatory substances to neurons but also for the formation of the blood-brain barrier, which is a crucial structure that prevents the entrance of harmful substances into the brain. Astrocytes maintain the extracellular environment and play a significant role in the chemical and structural support of the brain.