Another cell type is added to the list of those that can be produced on demand in the laboratory: "Pity the lowly astrocyte, the most common cell in the human nervous system. Long considered to be little more than putty in the brain and spinal cord, the star-shaped astrocyte has found new respect among neuroscientists who have begun to recognize its many functions in the brain, not to mention its role in a range of disorders of the central nervous system. [Now] a group [reports] it has been able to direct embryonic and induced human stem cells to become astrocytes in the lab dish. The ability to make large, uniform batches of astrocytes [opens] a new avenue to more fully understanding the functional roles of the brain's most commonplace cell, as well as its involvement in a host of central nervous system disorders ranging from headaches to dementia. What's more, the ability to culture the cells gives researchers a powerful tool to devise new therapies and drugs for neurological disorders. ... Not a lot of attention has been paid to these cells because human astrocytes have been hard to get. But we can make billions or trillions of them from a single stem cell. Without the astrocyte, neurons can't function. Astrocytes wrap around nerve cells to protect them and keep them healthy. They participate in virtually every function or disorder of the brain. ... They could be used as screens to identify new drugs for treating diseases of the brain, they can be used to model disease in the lab dish and, in the more distant future, it may be possible to transplant the cells to treat a variety of neurological conditions, including brain trauma, Parkinson's disease and spinal cord injury. It is possible that astrocytes prepared for clinical use could be among the first cells transplanted to intervene in a neurological condition as the motor neurons affected by the fatal amyotrophic lateral sclerosis, also known as Lou Gehrig's disease, are swathed in astrocytes."