Astrocytes (Astro from Greek astron = star and cyte from Greek "kytos" = cavity but also means cell), also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. The proportion of astrocytes in the brain is not well defined. Depending on the counting technique used, studies have found that the astrocyte proportion varies by region and ranges from 20% to 40% of all glia. Overall, astrocytes outnumber neurons by over fivefold. They perform many functions, including biochemical support of endothelial cells that form the blood–brain barrier, provision of nutrients to the nervous tissue, maintenance of extracellular ion balance, and a role in the repair and scarring process of the brain and spinal cord following traumatic injuries.