Final answer:
Astrocytes are responsible for the formation of the blood-brain barrier in the CNS, providing structural support and regulating the extracellular chemical environment for neurons.
Step-by-step explanation:
The function of astrocytes includes several crucial roles within the central nervous system (CNS). Astrocytes facilitate the formation of the blood-brain barrier (BBB), a structure that blocks the entrance of toxic substances into the brain.
Additionally, they regulate the concentrations of ions and chemicals in the extracellular fluid, provide structural support for neurons and synapses, and maintain the chemical environment necessary for proper neural function. They do not myelinate CNS axons, as this is the job of oligodendrocytes; they do not secrete and circulate cerebrospinal fluid, which is a function of ependymal cells; and they do not act as phagocytes, a role fulfilled by microglia.