Final answer:
Astrocytes are the glial cells responsible for maintaining the chemical environment around neurons and crucially regulating the blood-brain barrier, not ependymal cells which produce CSF.
Step-by-step explanation:
The cells that play a role in the establishment of the blood-brain barrier are known as astrocytes. These cells are one of several types of glial cells found in the central nervous system (CNS), which also include oligodendrocytes, microglia, and ependymal cells. Astrocytes have many functions, including the regulation of ions, uptake and/or breakdown of some neurotransmitters, and contributing significantly to the formation of the blood-brain barrier, which separates the circulatory system from the brain. While ependymal cells are responsible for creating cerebrospinal fluid (CSF), their role does not directly include establishing the blood-brain barrier.