astrocytes CNS glia that function to orient neuroblast migration in the cerebral and cerebellar hemispheres, provide mechanical support, react to injury, insulate synaptic surfaces, provide a source and sink for extracellular potassium, and uptake neurotransmitters to terminate their synaptic action astrocytoma most common central nervous system tumor derived from astrocytes astrocytosis reaction of astrocytes to neuronal injury characterized by an increase in the number and size of astrocytes (primary reaction) and cytoplasmic changes including increased glial filaments and glassy eosinophilic cytoplasm followed by formation of a dense gliotic scar (secondary reaction)