The central nervous system consists of neurons and glial cells. Neurons constitue about half the volume of the central nervous system 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 glia cells are: astrocytes, oligodendrocytes, and microglia.
