An astrocyte is a sub-type of the glial cells in the brain and spinal cord. It is also known as astrocytic glial cell. Its processes envelope synapses made by neurons. Astrocytes are classically identified histologically as many of these cells express the intermediate filament glial fibrillary acidic protein.
There are three types of astrocytes in the Central Nervous System, fibrous, protoplasmic, and radial. The fibrous glial cells are usually located within white matter, have relatively few organelles, and exhibit long unbranched cellular processes. This type has "vascular feet" that physically connect the cells to the outside of capillary wall when they are in close proximity of them. The protoplasmic astrocytes are found in grey matter tissue, possess a larger quantity of organelles, and exhibit short and highly branched cellular processes. Finally, the radial astrocytes are disposed in a plane perpendicular to axis of ventricles.