glia

n. Any tissue made up of glial cells, which are nonneural cells within the nervous system which provide structural support, nutrition, or other assistance to nerve cells. Two types of glial cells, oligodendrocites and Schwann cells, form the myelin sheath which surrounds nerve tracts and increases the speed of impulse transmission. Other types of glial cells include astrocytes, which are starshaped cells which outnumber neural cells by 10 to 1 in the brain; microglia, which provide immune function in the brain; and ependymal cells, which line the walls of the ventricles within the brain.