Radialglia, also known as radial glial cells, are multipotent stem cells. All neurons of the brain, astrocytes and oligodendrocytes, develop from them.
Radialglia are instrumental in structuring the developing brain.
Glial cells in the central nervous system – microglia
Microglia make up the second largest portion of glial cells in the central nervous system, accounting for 20% of all glial cells. Unlike the macroglia, they descend from the mesodermal germ layer. Accordingly, they also differ in their function from the macroglia.
Figure 4: Immunostaining of murine microglia (green) and nerve fibers (red); Source via wikipedia.org
Microglia are part of the immune system of the central nervous system. Microglia are basically inactive and must first be activated by an external factor.
Activated microglia function as macrophages. Macrophages are so-called scavenger cells. They can recognize, ingest and digest foreign bodies. This process is called phagocytosis. Recognizing potentially toxic substances is essential, especially at the blood-brain barrier. In this way, they protect the non-regenerable neurons. But even after an injury to the central nervous system, the microglia help to clean up dead nerve tissue.
Microglia can also activate and summon other microglia and other cells. As a result, they can either inhibit or induce an inflammatory response. Furthermore, they can stimulate astrocyte proliferation after injury. This then leads to the formation of glial scars.
Another task of the microglia is the regulation of neuronal progenitor cells in embryonic development.
Glial cells in the peripheral nervous system
In the peripheral nervous system you will find the Schwann cells and the mantle cells.
As mentioned above, they take over Schwann cells the same task as the oligodendrocytes: they encase the axons with myelin.
Between two Schwann cells there is always a small space. This is called Ranvier’s node and is essential for saltatory conduction.
A special feature of Schwann cells is the ability to assist in the regeneration of axons. This allows for the regeneration of neurons in the peripheral nervous system.
Mantle cells are also known as satellite cells or amphicytes. Mantle cells – as the name suggests – encase the neurons with a single layer, flat layer in the peripheral nervous system. This is how they delineate the neurons in the peripheral nervous system. Mantle cells regulate the metabolism of the neurons.
You can compare the mantle cells to the astrocytes in the central nervous system.