Microglia are a type of glial cell (neuron support cell) that serves an immunological function in the central nervous system (CNS). The term Microglial cells can be simplified as "microglia." Microglia is the glial cells which provide nutrition. It is compared with macrophages. About 15-20% of microglia are in the human brain and spinal cord. These cells protect the brain from invading microorganisms. The main function of microglia is clearing the dead cells to protect our body from a disease.
In 1880, Franz Nissl and F. Robertson first found out what microglia do. They showed that microglia are related to macrophages. In 1897, Victor Babes found out about the activation of microglia and formation of ramified microglia clusters. He found that the microglial cells are found in a variety of viral brain. In 1920, Pio del Rio-Hortega first called the cells “microglia”. In 1932, he found out about the “fountains of microglia” are in the corpus callosum and white matter areas. For many years, Rio-Hortega searched more about microglia and he is known as the father of microglia. In 1988, Hickey and Kimura found out about “perivascular microglial cells” that are bone-marrow derived. They showed that function of microglia cells and macrophages are similar. 
Microglia are known as the macrophages of the central nervous system (CNS) which remove the toxic and dead cells. They both act as immune cells in CNS. Microglia mostly act in CNS trauma, apoptosis, ischemia, and etc.
There are some major functions of microglia. First, microglia clean up the various materials such as damaged cells, dead cells, viruses, bacteria, and other foreign materials. This activity is called phagocytosis. Microglia contain cytotoxicity. Cytotoxicity helps microglia to destroy or remove infected organisms, but it can cause a collateral neural damage. When there is a neural damage, microglia can regenerate and repair the damaged tissue by removing branches. This also is one of the function of microglia. When there are less microglia, the damage in the brain and eyes, areas of CNS, wouldn't or would slowly regenerate. Because these cells maintain homeostasis, microglia protect the areas of brain. 
Types of microglial cells
There are five types of microglial cells.
Ameboid cells are found in white matter areas. These areas are in the corpus callosum.
Ramified microglia possesses proliferative capability.
This is the white blood cells. It protects our body from bacteria and dead cells. 
It is called as a "compound granule cell" or "compound granular corpuscle." It is found in the basal lamina wall.
This is one of the connective tissue cells.
This is found in the wall of the blood vessels. It is very similar to perivascular cells. 
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