astrocytes are the largest type of glia, and may affect the growth of neurons due to their close proximity. They perform nutritive and metabolic functions to neurons, and regulate chemical content of extracellular space (such as determine how far neurotransmitters released into the synapse can travel.
-Oligodendrocytes make myelin for the axons of the brain and spinal cord. Myelin on other axons is produced by schwann cells.
-Microglia are phagocytes that remove debris from the nervous system (which accumulates from injury, aging, disease, etc.) Microglia are produced by macrophages outside of the brain and spinal cord.