[MUSIC] Okay, neurons are the star of the show, there's no question but neurons don't exist on their own, they need Glia cells. So, glia cells are not the star, they're the supporting cast. But just as a show does not go on without the supporting cast, the brain does not function without glia. So, we're going to look at glia for just one short segment. There are few different types but before we get to the types, I want to tell you that the reason I'm telling you about this is because when we originally gave this course I was contacted by a student who said, you said something wrong. The thing that I said that was wrong is that I said that there are ten times more glia than there are neurons. And what you'll see is that, that is contained in every textbook that I am aware of, including my own. So the student wrote me and said, you know that's not actually the case and there is a woman, a Brazilian neuro scientist named Suzana, Herculano Houzel. I'm not sure if I'm saying that correctly but that's her name, who has very carefully and methodically counted the number of neurons and the number of glia cells in a wide variety of animals, lots of different mammals, including humans, including mice, and rats, and elephants. What she has to say is endlessly fascinating, really worth reading about. But when she counted glia cells in the human brain, when she counted the neurons and glia cells, what she found out was that the brain contains 86 billion neurons and 85 billion glia. For a ratio of 0.99 which we're going to say equals 1. So there is a one to one relationship between the number of neurons, and the number of glia in the human brain, and pretty much in other animals it's not far off that either. Okay, so there are not more glia than neurons. That's just false. Okay, so what are different types if glia? Well, there are Astrocytes and Astrocytes are really important type of Glia. They're essentially responsible for keeping the environment clean, they're the sanitation worker of the brain, if you will. So they are picking up all this refuse that the neurons have let loose including excess ions, excess non-transmiters and their metabolites. They're cleaning up. They also are very important during development. They allow neurons to get to where they have to go during development. Neurons are born in one place and they have to go some place else, and what highway did they take? They hitch on a progenitor cell that is going to become Astrocytes. And, in addition when synapses are formed, the synapses are not or not maintained without some effort and part of that is that the synapses are enveloped in the processes of Astrocytes. So, there's a lot of structural and metabolic support that the Astrocytes are providing for neurons. And then there are these two different types of glia cells. Both of these glia cells make myelin. And the oligodendrocytes make myelin in the CNS and the Schwann cells make it in the Peripheral Nervous System. So all these demyelinating diseases will affect either central myelin or peripheral myelin. They will not affect both, central or peripheral. Because they are made by two different types. The Oligodendrocytes in the central nervous system and a Schwann cells in the peripheral nervous system. Now it turns out that this is about, Astrocytes can comprise about 20% of all the Glia cells, and these Oligodendrocytes comprise about 75% of the central glia cells. The remainder are these microglia, and microglia are the one exception to the rule that nervous system, that the cells of the nervous system come from Ectoderm. These are actually essentially immune cells coming from the blood lineage. These are immune cells that have invaded into the central nervous system and their job is to be quiet. And if we're healthy and everything goes well, they are quiet. But when there is a problem these microglia react, they try to rectify things, they try and bring some attention to areas of damage and what is emerging is that sometimes they go overboard and they start to participate in making the problem as well as solving the problem. Microglia are a hot topic. They are implicated in all manner of diseases from chronic pain, from maintaining chronic pain, conditions through all the neuro general disorders such as Alzheimer's and so on. So this is a very hot topic of research right now. These are the glia and we're probably not going to talk about the poor, underappreciated glia again. But there they are. [MUSIC]
