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This video describes the structure and function of microglia. Microglia, the smallest glial cells in our central nervous system, play a crucial role in maintaining brain health. Originating from the mesoderm, they transform from resting to active states to combat inflammation. Active microglia act like macrophages, eliminating foreign cells and debris through cytotoxic factors and phagocytosis, and presenting antigens to immune cells. By Matt Jensen. Created by Matthew Barry Jensen.

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  • blobby green style avatar for user Djoka
    At , what does he mean by "micriglia also contributes to inflammation". Why would microglia contribute to inflamation instrad of stopping it?
    (14 votes)
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    • male robot hal style avatar for user Arnout Verheij
      In this case microglia contibute to this process by:
      - Releasing Cytokines (activates various immune cells), Chemokines (attacks immune cells) and other secretions. This leads to more inflammation.
      - Presenting cells so that specific immune cells (T and B) can recognize the antigens and react to them.

      Now this all leads to more inflammation. If all the invading microorganisms have been cleared the mircoglia stop with secreting and presenting. Then the inflammation will subside.

      PS: Inflammation is just a proces of the immune system. It does not have to be specific to an invading organism, it can be directed at the host own cells.

      Hope this helps!
      (18 votes)
  • blobby green style avatar for user Victoria Burmester
    Thanks for posting this video.

    1. Why are microglia not considered part of the immune system?
    2. If microglia destroy bacteria and other undesirables then consume them, why do they then need to present them for other cells, creating inflammation?
    (8 votes)
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    • aqualine ultimate style avatar for user Katarzyna Pałucka
      1. The origin of microglia is still disputable, and there are two main theories that derive them from two different layers of the embryo: the first one from mesoderm (as presented in the video), and the second one from ectoderm. The first one suggests that microglia have the same origin as immune cells (what would place them in that category), and the second that their origin is similar to the other neural cells. This question doesn't have the answer jet, as we have to wait for more research about that problem.
      2. The fact that it destroyed some bacteria doesn't have to mean that the infection is under control. The act of antigen presentation influences lymphocytes and creates immunity to whatever the antigen was, enabling the organism to fight with the pathogen. Inflammation is therefore desirable, as it is the state in which the immune cells are most effective in eliminating pathogens, which may be still present in the organism.
      (6 votes)
  • blobby green style avatar for user robmielczarek
    This is my first question on KA so I hope it's phrased correctly-
    if microglia originate from monocytes, where do the monocytes come from?
    Similarly, when a microglia is acting as a APC, where do the other leukocytes enter/exit the brain? Can they cross the blood-brain barrier or do they somehow bypass using the lymphatic system?
    (5 votes)
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    • leaf orange style avatar for user Tanj
      Monocytes develop in the haemopoietic bone marrow (red marrow). Monocytes roam around the circulatory system for a while until they enter other tissues. They differentiate into other specialised cells that more-or-less are the same ('macrophage') but with different names and jobs: Microglia, Kupffer cells, dendritic cells, alveolar macrophages...

      When a microglial cell meets a non-self object like a bacterium, the recognition of non-self antigens causes it to self-activate and induce inflammation by releasing cytokines and chemokines (which might enhance inflammation already present). Some of the chemicals released act on the capillaries in the brain, allowing them to become "leaky". The combination of chemokines and leaky vessels helps attract and allow other leukocytes to enter the BBB. This also allows bacteria and antibiotics to also cross the barrier.
      (9 votes)
  • duskpin ultimate style avatar for user The Q
    Whats to distinguish resting microglia from astoocytes?
    (5 votes)
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  • primosaur tree style avatar for user Shreya
    How, exactly, do microglia react to physical injury not caused by any invading pathogen?
    (3 votes)
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  • blobby green style avatar for user Ivelisse_diaz
    Just out of curiosity...
    Inflammation seems to be a key environment for the functioning of microglia and immune cells... so why do we always try to reduce inflammation when there is an injury of some sort? I understand that it could help alleviate pain for the patient but is there any other benefit to reducing inflammation?
    (2 votes)
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  • blobby green style avatar for user burce isik
    I need a clarification on microglia arise from mesoderm. Can we say mesoderm give rise to nerve cells then? How is it possible that they are formed from mesoderm since they are CNS cells which arise from ectoderm? Also since mesoderm is derived from ectoderm, isn't it technically derived from ectoderm. not sure what to answer if this comes up on mcat...
    (2 votes)
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  • blobby green style avatar for user Mitchell Chu
    At , he refers to presenting the debris that has been phagocytosized. That debris would include self-cells that are damaged, how does the microglia cell prevent the presentation of those self-cell antigens and the presentation of only foreign antigens?
    (1 vote)
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    • leaf blue style avatar for user dysmnemonic
      Microglia don't express MHC II or co-stimulatory molecules unless they've had an activating signal, which helps to protect the CNS from autoimmunity. Typically the activating signal will be from detecting a clearly foreign molecule in the phagocytosed material, which then tells the microglial cell that it needs to put out the signal to the immune system.
      (2 votes)
  • aqualine seed style avatar for user shafiq amar
    hi , what does microglia origination and what is its function in HIV?
    (1 vote)
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  • blobby green style avatar for user shubhajain1901
    What will happen if aggregated Tau protein would be added to microglia cells?
    (1 vote)
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Video transcript

In this video, we're going to talk about microglia, which are glial cells of the central nervous system. Their name comes from Greek words meaning "small glue," which doesn't actually make a lot of sense. But when all the glial cells were having their names handed out, the microglia were noticeably smaller than all the other glial cells. So the cells ended up being named microglia. And all the other glial cells will sometimes be referred to collectively as macroglia because they all tend to be larger than the microglia. Most or all microglia probably derived from circulating monocytes from the bone marrow, that then enter the central nervous system. So that they are therefore from the part of the embryo called the mesoderm, as opposed to the ectoderm that all the other neural cells are derived from. Microglia come in a few different shapes. Resting microglia have a small soma and lots of long, highly branched processes heading out in every direction. And when they're in this shape, they're called resting microglia. Active microglia are larger and just kind of blob shaped. Some people say they're shaped like an amoeba. So when they're shaped like this, they're called active microglia. When microglia are resting, they're basically just sitting there sampling the interstitial fluid. They have all these long, highly branched processes heading out, just keeping an eye on the interstitial fluid. And they're basically looking for trouble. And when resting microglia do detect that there's trouble going on, they convert into active microglia. They retract all these long, branch processes and turn into these blob-like active microglia. And the main type of trouble they're looking for is inflammation. And whether that's inflammation from injury to the tissue of the central nervous system or an infection of some sort, like a bacteria or a virus has entered the central nervous system. Now active microglia look and act like macrophages anywhere else in the body, which is a type of cell that moves around through tissues looking for dead or damaged cells or foreign cells. So active microglia will move or migrate over to areas of inflammation and they're looking for things like bacteria or other foreign cells that have invaded and are causing an infection or dead or damaged cells of the central nervous system. Now, if an active microglia finds a foreign cell like a bacteria, it can secrete substances that are called cytotoxic, that can kill these foreign cells. For example, reactive oxygen species-- that I'll just shorten to "ROS"-- that could kill a cell like a bacteria. And secretion of cytotoxic factors is one of the main functions of microglia. Now after the microglia killed the bacteria, the bacteria would turn into just debris, just broken up pieces of bacteria. And there is nothing that microglia enjoy more than chowing down on debris. And it doesn't have to be foreign cell debris, like a bacteria. But any cell of the central nervous system, if it's dead or its damaged and there's debris, basically anything that's not a normal healthy cell of the central nervous system, the microglia will eat it. It'll take it inside its own cell and break it down into smaller pieces. So this is another main function of microglia, which is called phagocytosis, which means eating cells or eating debris. Just like other types of cells do all over the body, when they're like macrophages, they look just like active microglia. Now, these functions don't have to occur in this order. If a microglia bumps into something abnormal and phagocytoses it, that often gets the microglia fired up and it may then start at creating cytotoxic factors, or other substances that interact with immune cells to further fire up information. Now after the microglia eats the debris, it performs its next major function, which is to take those broken up pieces of the debris that it ate and stick little pieces out on its surface for other cells to see and specifically other cells of the immune system, like lymphocytes. Lymphocytes will come in here and they will recognize or they'll look at these pieces of the debris that the microglia ate and is now presenting on its surface for the lymphocyte. Any molecule that a cell of the immune system can recognize, we call an antigen. So this function is called antigen presentation. With the effect that these immune cells further increase inflammation and try to make the inflammation more specific to whatever the antigen was, particularly if it's from a foreign cell. So that the microglia is activated by inflammation and the microglia also contributes to inflammation. Therefore, microglia play a major role in inflammation in the central nervous system. In addition to these functions, microglia appear to influence neurons, other glia, and other cells of the immune system and vice versa, through exchange of a variety of substances.