Glial cells outnumber neurons in the central nervous system and provide support and protection for neurons. There are several types of glial cells - astrocytes, oligodendrocytes, microglia, and ependymal cells. In disease states, glial cells can become reactive or activated and contribute to conditions like stroke, cerebral edema, Alzheimer's disease, neuropathic pain, epilepsy, and glioma. The document provides an overview of glial cell types, functions, pathophysiology, and their involvement in specific nervous system diseases and conditions.