What is the function of astrocytes
from Latin: astrum - star
Synonym: spider cell
The Astrocytes are cells of the glia of the central nervous system (neuroglia). Astrocytes can be distinguished from other glial cells by their pronounced cell processes ("rays").
Astrocytes are not identical to stellate cells. The terms are not to be treated synonymously, despite the apparent translation from Latin.
Astrocytes have a relatively small cell body (soma) with a diameter of 10-20 μm. However, they have numerous cell processes extending radially from the cell body, some of which are branched and cover the surfaces of neighboring nerve cells. Due to the dense accumulation of their processes and cell bodies, they form the following layers in the CNS:
The cell connections are represented by gap junctions (electrical coupling) and zonulae adhaerentes (mechanical coupling).
The exact shape of the astrocytes is apparently modulated by their neural environment. In vitro it has been shown that astrocytes can swell or shrink depending on the neural activity in their vicinity. The same seems to apply to the formation of cell processes (filopodia). This phenomenon is aptly referred to by some authors as "infotropism".
Based on their morphology, the following types can be distinguished:
- Fibrillary astrocytes (Astrocytus fibrosus) or fiber astrocytes have numerous slender and less branched cytoplasmic processes ("long rays"). They are mainly found in the white matter.
- Protoplasmic astrocytes (Astrocytus protoplasmaticus) have richly branched, thick cytoplasmic processes ("short rays"). They are characteristic of the gray matter.
- Plasmatofibrillary Astrocytes are on the border between white and gray matter.
Another important function of the astrocytes is the evaluation and modulation of neural activity. By releasing growth factors such as BDNF and GDNF, neurons form new synapses or ensure their preservation. Some neurons can only transmit their signals because neighboring astrocytes contribute D-serine and glutamate and secrete them into the synaptic cleft.
Astrocytes in certain areas of the brain can possibly take over the function of stem cells for neurons. If the gene for neurogenin-2 is smuggled into cultivated astrocytes, the cells show the typical shape of nerve cells after a short time in laboratory experiments and develop functional synapses.
Brain tumors that are histologically derived from astrocytes are called astrocytomas. The increased occurrence of hypertrophic or hyperplastic astrocytes is called astrogliosis.
The glial filaments contained in the cytoplasm of astrocytes consist of the acidic glial fiber protein GFAP. The protein is used as a tumor marker.
At gemistocytic astrocytes are swollen astrocytes with eosinophilic plasma that occur in demyelinating diseases or neoplasms.
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