Microglia

This is an image of cells in the brain including microglia

Microglia is a term that is used to describe the tissue-resident macrophages of the central nervous system. These macrophages were originally classified as glial cells, under the assumption that the cells had a merely structural function, before it was realized that the cells were in fact immune cells. As the tissue-resident sentinel cells of the central nervous system, microglia survey their environment for abnormalities such as infection or tissue damage, and then initiate an immune response to fight the infection or repair the tissue damage.

Microglia Activity

Microglia function in multiple capacities:

Apoptosis

One of their functions is to clean up the remains of a cell after it has apoptosed (self induction of cell death). This is important because the contents of a cell can be harmful when not contained by cell or organelle membranes. The microglia when activated takes on a blob-like structure and ingests the dead cell and its contents. Microglia can also prompt cells to become apoptotic.

Neural Pruning

Microglia also prune neurons at the synapses, which are the spaces between neurons across which neurotransmitters travel. If these are damaged, dysfunctional or underused microglia will repair or remove the problem area. This function of microglia is important to development but may become harmful during neuroinflammatory events. During inflammation of the brain, the microglia may prune too much causing a loss of synaptic integrity.

Priming and Microglia Activation

Several events can cause microglia to become primed. Priming means that microglia will respond more aggressively and more easily to activating factors, and occurs when the microglia are over-exposed to harmful events or stimuli. One of the events that can prime microglia is aging. Usually, cells in the body are continuously recycled and regenerated so that they function like new. Microglia are not replaced often, however,  and can wear from use.

Infections can also cause microglial priming. During an infection, immune molecules called cytokines circulate throughout the body. Some of these molecules can get directly into the brain and activate microglia, or they can indirectly activate microglia through neural signaling of the vagus nerve. If an infection persists for an extended period of time, microglia will continuously be activated and may become damaged from use.

Traumatic brain injuries also prime microglia. Direct damage to the brain (e.g. concussion, stroke or blunt force trauma) causes the microglia to work continuously to resolve the damage. The damage itself also causes the release of inflammatory markers that activate the microglia. Continued functioning can cause persistent symptoms of the initial damage.

Notable studies

• 2019, Evidence of widespread metabolite abnormalities in Myalgic encephalomyelitis/chronic fatigue syndrome: assessment with whole-brain magnetic resonance spectroscopy
• 2019, Hyperactivation of proprioceptors induces microglia-mediated long-lasting pain in a rat model of chronic fatigue syndrome (Full text)

See also

• Macrophage
• Glial cell
• Nervous system
• Alzheimer's
• Dorsal root ganglia
• Jarred Younger
• Low dose naltrexone

Learn more

• Cell Motility of Microglia Cultured in TIC by Cell Press via YouTube
• Depletion of microglia and inhibition of exosome synthesis halt tau propagation by Research Square via YouTube
• 2-Minute Neuroscience: Glial Cells by Neuroscientifically Challenged via YouTube
• February 21, 2018 - Microglia in Fibromyalgia and Chronic Fatigue Syndrome by Adrienne Dellwo for Very Well Health

microglia A type of immune cell, called a macrophage, that lives in the brain. For historical reasons, macrophages have different names based on the part of the body that they normally live in. Macrophages that normally live in the blood are called monocytes. Macrophages that normally live in the skin are called Langerhans cells. Macrophages that normally live in the liver are called Kupffer cells. And macrophages that normally live in the central nervous system are called microglia. Microglia were originally classified as glial cells, under the assumption that the cells had a merely structural function, before it was realized that the cells were in fact immune cells. As the "sentinel cells" of the central nervous system, microglia survey their environment for abnormalities such as infection or tissue damage, and then initiate an immune response to fight the infection or repair the tissue damage.

microglia A type of immune cell, called a macrophage, that lives in the brain. For historical reasons, macrophages have different names based on the part of the body that they normally live in. Macrophages that normally live in the blood are called monocytes. Macrophages that normally live in the skin are called Langerhans cells. Macrophages that normally live in the liver are called Kupffer cells. And macrophages that normally live in the central nervous system are called microglia. Microglia were originally classified as glial cells, under the assumption that the cells had a merely structural function, before it was realized that the cells were in fact immune cells. As the "sentinel cells" of the central nervous system, microglia survey their environment for abnormalities such as infection or tissue damage, and then initiate an immune response to fight the infection or repair the tissue damage.

central nervous system (CNS) - One of the two parts of the human nervous system, the other part being the peripheral nervous system. The central nervous system consists of the brain and spinal cord, while the peripheral nervous system consists of nerves that travel from the central nervous system into the various organs and tissues of the body.

apoptosis a type of cell death in which a cell, in response to a threat, initiates a series of molecular steps that lead to its orderly death. This is one method the body uses to get rid of unneeded or abnormal cells. This form of cell suicide is also called programmed cell death.

membrane The word "membrane" can have different meanings in different fields of biology. In cell biology, a membrane is a layer of molecules that surround its contents. Examples of cell-biology membranes include the "cell membrane" that surrounds a cell, the "mitochondrial membranes" that form the outer layers of mitochondria, and the "viral envelope" that surrounds enveloped viruses. In anatomy or tissue biology, a membrane is a barrier formed by a layer of cells. Examples of anatomical membranes include the pleural membranes that surrounds the lungs, the pericardium which surrounds the heart, and some of the layers within the blood-brain barrier.

apoptosis a type of cell death in which a cell, in response to a threat, initiates a series of molecular steps that lead to its orderly death. This is one method the body uses to get rid of unneeded or abnormal cells. This form of cell suicide is also called programmed cell death.

microglia A type of immune cell, called a macrophage, that lives in the brain. For historical reasons, macrophages have different names based on the part of the body that they normally live in. Macrophages that normally live in the blood are called monocytes. Macrophages that normally live in the skin are called Langerhans cells. Macrophages that normally live in the liver are called Kupffer cells. And macrophages that normally live in the central nervous system are called microglia. Microglia were originally classified as glial cells, under the assumption that the cells had a merely structural function, before it was realized that the cells were in fact immune cells. As the "sentinel cells" of the central nervous system, microglia survey their environment for abnormalities such as infection or tissue damage, and then initiate an immune response to fight the infection or repair the tissue damage.