There’s a common brain myth that you “only use 10% of your brain”. The movie Lucy capitalizes on this idea, starring Scarlett Johansson as a woman who “unlocks” the other 90% and, as a result, is capable of feats of strength, time travel, and telepathy. Perhaps unfortunately (time travel sounds sweet!), this is nothing more than an interesting and oft-quoted myth, and has no basis in reality. But if that’s true, where did the myth come from? It may be because only 10% of the cells in your brain are neurons, and they get all of the attention. This makes a lot of sense – your neurons are responsible for making all of the connections to contain all of your memories, and for sending all of the signals that allow you to walk, talk, and interact with the world. It’s pretty apparent that these cells are superstars; they do a lot of work and get a lot done. But if only 10% of your brain cells are neurons, what makes up the other 90%, and what are they even good for?
The other cells in your brain are collectively called “glia”, which literally translates to “brain glue”. Scientists lumped all of these cells together because for many, many decades, we assumed that they were pretty unimportant. Because these cells act as scaffolding to hold the neurons in place, insulation to help the neurons send signals better and faster, and providers of nutrients and oxygen to keep neurons alive and healthy, we wrote off 90% of the brain as static and uninteresting, and focused all of our attention on the exciting, active neurons. Think about it this way: we care about Beyoncé and the next album she puts out, but we don’t spend too much time thinking about the people who do her make up, tailor her clothing, or construct her music videos. Just because we don’t notice them doesn’t mean they aren’t vital to keeping Beyoncé as vibrant, talented, and visible as always. No entourage means no Beyoncé, even if she’s the stunning face we all see. Beyond their support roles, there’s more and more evidence that some of these “boring” glial cells are actually really important to helping your neurons form and maintain their connections with one another.
Within the category of glia, we have a few major cell types:
- Oligodendrocytes are considered the brain’s insulation. They use their cell membranes to wrap around the long, slender axon of a neuron, insulating the axon so that the neuron’s signal can travel faster down the length of the cell. Since neuronal axons can get pretty long (your sciatic nerve runs all the way from the base of your spine to your foot!) it’s important to have insulation to send fast signals to your brain.
- Microglia are important for the brain’s immune system. These cells travel around the brain, cleaning up dead cells, debris, and infectious intruders, keeping things healthy. They may also help prune your neurons to ensure they make appropriate connections.
- Astrocytes are my favorite brain cell (maybe you could have guessed that from my name!) They act as important scaffolding for your neurons and provide them with oxygen and nutrients, but that’s not all they do – they also play important and active roles in the connections in your brain! Your neurons connect with one another at spots called synapses. These are gaps between the individual cells, and your neurons communicate with each other by sending chemical signals across those gaps, called neurotransmitters. Astrocytes often have long, skinny bits, called processes, wrapped around these synapses. They can help control the signal by cleaning up extra neurotransmitter at the gap, and by providing the neurons with new materials to make more neurotransmitters. These astrocytes also release different proteins that can affect the structure and function of the synapse. We’ve learned that astrocytes are vital for helping properly form certain types of connections, and they may also be important for changing and adapting connections during learning and memory formation.
I find glia exciting because we’re learning new things about them every day; our research on the brain has demonstrated that it’s a dynamic and complicated organ, and these underappreciated cells are no exception. My own research focuses on trying to better understand how glia influence synapse formation and what can go wrong during that process. I’ll be posting more here about new and exciting research centered on glial cells and their roles in the brain. I want to provide a behind-the-scenes glimpse at the life of the “neuron-tourage” keeping those neurons so fresh and healthy; I hope you’ll come back to learn more soon!