Author: Nina Stöberl
Many of you have probably heard of neurons, the basic working unit of our nervous system and our brain. They transmit information to other nerve cells, muscles and glands and they are the reason that we can move and think.
However, the brain contains at least as many glia cells as neurons (though defining this ratio is still a matter of research). In Greek “glia” means glue and this describes perfectly what scientists thought about these cells for a long time, namely that they hold neurons in place.
Nowadays we know that glia cells have lots of important roles in the brain including an active role in the transmission of information, supplying neurons with nutrients and oxygen, and maintaining a healthy brain environment.
Glia cells are actually a group of different cells that can be further divided into macroglia and microglia, which are basically defined by their size: macroglia are big, microglia are small.
So does this mean microglia are just the “small glue” of the brain? To say yes wouldn’t do justice to their broader impact and function. Microglia are the resident immune cells of the brain and behave like macrophages, which are their immune cell equivalent elsewhere in the body. Macrophage, however, translates to “big-eater” in Greek, which I think is a much better name for these amazing cells.
The main function of our brain microglia is to eat the debris or trash in our brain, such as dying neurons. As immune cells, they protect the brain from infectious agents before these can harm neurons. Microglia also help to make the brain more efficient during development by eating up redundant connections between neurons.
Today, microglia research is a hot topic and these cells are getting a lot of attention. Many human genetic studies conducted over the last few years have determined that microglia are involved in many neurodegenerative disorders, including Alzheimer’s disease. These studies showed that microglia have important functions far beyond acting as a “glue” between neurons which progressively die in these debilitating diseases. However, scientists are still unsure if microglia help or hurt in the progression of neurodegenerative diseases. To find out, more and more researchers are now investigating microglia, hoping to identify precisely how they impact human health and disease.
Image taken from:
Sierra et al., 2016: The “Big-Bang” for Modern Glial Biology: Translation and Comments on Pío del Río-Hortega 1919 Series of Papers on Microglia. Figure I.1 Main types of normal human microglia
References and further reading:
https://www.healthline.com/health/neurons
https://www.neuroscientificallychallenged.com/glossary/glia
https://www.vettimes.co.uk/the-big-eater/
https://www.britannica.com/science/microglia
Bartheld et al., 2016:The search for true numbers of neurons and glial cells in the human brain: A review of 150 years of cell counting (doi: 10.1002/cne.24040)
Hansen et al., 2018: Microglia in Alzheimer’s disease (doi: 10.1083/jcb.201709069)
Hickman et al., 2018: Microglia in neurodegeneration (doi: 10.1038/s41593-018-0242-x)