The central nervous system consists of neurons and glial cells. Neurons constitue about half the volume of the CNS and glial cells make up the rest. Glial cells provide support and protection for neurons. They are thus known as the "supporting cells" of the nervous system. The four main functions of glial cells are: to surround neurons and hold them in place, to supply nutrients and oxygen to neurons, to insulate one neuron from another, and to destroy and remove the carcasses of dead neurons (clean up). The three types of CNS supporting cells are Astrocytes, Oligodendrocytes, and Microglia. The supporting cells of the PNS are known as Schwann Cells.
From Tripod. Text posted here because I could not link to the actual page, but I needed to be able to retrieve the information; the URL address stopped at www.tripod.com.