Neuro Primer: Glia
Every single day, a group of cells work tirelessly to monitor and protect the neural architecture of your brain. Some of them even move around, scanning neural networks like recon drones in video games. When they detect a threat, they can even change their shape to attack intruders that might be harmful to the rest of your brain.
But these cells aren’t neurons. They’re called glia.
Glorious glia are the sentries and protectors of our brains – yet we’re just now starting to understand the array of functions these cells carry out and the intricate details of how they work. Glial cells, which get their name from the Greek word for glue, were first discovered in the early to mid 1800s. They were originally noted by French physician, Rene Dutrochet, as he was studying the nervous system of the mollusk and stumbled across small “globules” among the larger ones in the nervous tissue. About 30 years later, German pathologist Rudolf Virchow also came upon them in his study of the brain, thinking that they were some kind of connective tissue holding neurons together. He thereby named them “nevernkitt”, or “nerve-glue”, which translated to neuroglia (or glia). As time went on, other scientists (such as the famous Santiago Ramón y Cajal, who is best known for his detailed scientific illustrations of neurons) contributed their own hypotheses and observations to contribute to a further characterization of these mysterious cells.
The collective research of these scientists has led us to understand that glial cells are not just sticky scaffolding for neurons to grow on. They also feed neurons with vital nutrients and precious oxygen, as well as help regulate the internal environment of the brain (otherwise known as homeostasis). Glial cells also play key roles in the creation of new synapses (synaptogenesis) and the adaptability of the brain through processes like synaptic plasticity. When neurons communicate with each other by releasing neurotransmitters across the gap known as the synaptic cleft, a special type of glial cell called an astrocyte helps clear the “used” neurotransmitters out of the space, thereby preventing a toxic build-up of these molecules. Other types of glial cells – such as microglia, oligodendrocytes, and ependymal cells – also help neurons develop, migrate, grow, thrive, and stay healthy in the dynamic environment of the brain. Microglia, in particular, have exhibited remarkable protective features by directing the overall immune response to damage in the brain and handling the inflammation that accompanies it.
Scientists used to think that glial cells far outnumbered neurons (about 10x more), but more recent research seems to suggest that glia and the neurons they look after might actually exist in varying ratios, depending on the area of the brain. In areas like the cerebral cortex, for example, glial cells (or non-neuronal cells, in general) most likely exist in about a 1:1 ratio; whereas in areas like the cerebellum, glial cells are likely in the minority at a ratio of about 0.23 to 1.
While the study of neuroscience has been around for centuries, glial cells themselves are incredibly new to the field. There is still much to learn about the variety of these cells, from the range of functions they perform to the exact mechanisms of how they do so. Many of these cells are also involved in a variety of neurodegenerative diseases, as well, such as Alzheimer’s disease and Lou Gehrig’s disease. Unlocking the mystery of how these busy little “globules” protect the brain and help it thrive could help us develop potential treatments for such diseases in the future. Moreover, it would help us better understand our brains themselves, from big concepts like how our brains adapt to the more specific concepts like how we form new memories. Despite all the mysteries and big questions, one thing is for sure – the field of neuroscience has so much more to explore thanks to these crucial little cells in our brain.
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References/Resources:
Azevedo, F. A., Carvalho, L. R., Grinberg, L. T., Farfel, J. M., Ferretti, R. E., Leite, R. E., … & Herculano‐Houzel, S. (2009). Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled‐up primate brain. Journal of Comparative Neurology, 513(5), 532-541.
Brown University Wiki. (2010). History of Glia. Brown University. Retrieved from: https://wiki.brown.edu/confluence/display/BN0193S04/History+of+Glia
Chung, W. S., Allen, N. J., & Eroglu, C. (2015). Astrocytes control synapse formation, function, and elimination. Cold Spring Harbor perspectives in biology, a020370.
Ndubaku, U., & de Bellard, M. E. (2008). Glial cells: old cells with new twists. Acta histochemica, 110(3), 182-195.
Thomas, Ben. (2013). A Secret Society of Cells Runs Your Brain. Scientific American. Retrieved from: https://blogs.scientificamerican.com/mind-guest-blog/a-secret-society-of-cells-runs-your-brain/
von Bartheld, C. S., Bahney, J., & Herculano‐Houzel, S. (2016). The search for true numbers of neurons and glial cells in the human brain: a review of 150 years of cell counting. Journal of Comparative Neurology, 524(18), 3865-3895.
