Role of Astrocytes in the Central Nervous System:
Astrocytes or astrocytic glial cells collectively form astroglia, star-shaped cells surrounding neurons in the brain and spinal cord, outnumbering neurons 50:1, and are very active in the Central Nervous System, and not, as previously through, mainly “filler” cells. Non neuronal cells in the nervous system are glial cells, and astrocytes constitute a subtype of this category. They serve to maintain, support, and repair the nervous tissue that they serve, and are responsible, in large part, for the plasticity of the nervous system. They also modulate synaptic transmission by making and releasing glutamate, the principle excitatory neurotrans, and their many process often envelope neural synapses. Research suggests that astrocytes communicate with neurons through the release of transmitters, known as gliotransmitters, through a calcium ion dependent mechanism.
Fibrous, Protoplasmic, and Radial Astrocytes:
There are three forms of astrocytes in the CNS. These are, fibrous, protoplasmic, and radial astrocytes. Fibrous astroglia are generally found in white matter, have few organelles, and long unbranched processes. Protoplasmic glia have a huge quantity of organelles relative to fibrous cells, with short and highly branched cellular processes. They are generally found in gray matter. Radial astroglia exist at the intersection of gray matter and the pia mater, which is the innermost layer of the membranes surrounding the brain and spinal cord. Radial glia are also found in the vertebrate eye, where they form the Mueller Cells of the retina, and as Bergmann glia, epithelial cells in the cerebellum. are part of the radial glial cells.
Many primary astrocytes express GFAP, the intermediate filament glial fibrillary acidic protein, a characteristic trait.