First discovered by Santiago Ramon y Cajal (1832-1934) in 1891, they are cell types in the central nervous system (astroglial cells and oligoglial cells) connected to neural cells and, in contrast to these cells, having no role in information transport over long distances (i.e., in the conduction of nerve impulses). Moreover, unlike neurons, they are capable of mitosis. They do, however, support non-neuronal cells of the nervous system. In development, they perform the special function of supplying guides to the migration of neurons on their extended processes; other glial cells form the myelin sheaths of axons. The average number of glial cells in the adult cerebral cortex has been estimated at 39 billion for young adults and at 36 million for older adults. Such estimates indicate that the average number of glial cells in the brain exceeds that for neurons by 10-50 times (a fact that led to media-generated claim that we only use about 10% of our brains). The term ‘glia’ is derived from the Greek for ‘glue’, as is a legacy from 19th century neuroanatomy when is was widely held that they in some way ‘held’ the nervous system together. Glial cells were brought to public attention when the brain of Albert Einstein (1879-1955) was subjected to extensive neuroanatomical research by Marian C. Diamond and colleagues. Published in 1985, findings indicated that while the brain weighed less (1230 gr) than the human adult average (1360 gr), his brain had overabundance of glial cells (especially astrocytes) relative to gray cells, especially in the left hemisphere of Brodmann’s area 39 (parietal cortex).
See Astrocyte, Brain (or encephalon), Cell migration, Ependymal cell, Glioblasts, Mitosis, Myelin, Myelination, Neural crest, Notch, Parasympathetic nervous system (PNS), Parietal cortex, Proliferative ventricular zone, Purines, Purkinje cell layer, Radial glial cells