 You think that the neuron is the most important cell in the nervous system because we have talked only about neurons so far, but the fact is only 10% of nervous tissue is made up of neurons and the rest of it are glial cells. And glial cells are, oh, we love them. Okay, there we go. Neuroglia, that's another name for them, indicating that they are part of the nervous system. Now, we can sort our glial cells into two categories and we can sort them by where they're found. Four of our six are found in the central nervous system. The other two are found in the peripheral system, but we can almost think of them as having... The ones found in the peripheral system, nervous system have counterpoint, counter, what? Counter something, counterparts. Counterparts in the central nervous system. Oh, man, so let's sort them in all sorts of different ways, shall we? First of all, I want to sort out the ones that are not found in the peripheral nervous system and those are my appendable cells, holy hell, my appendable cell and my microglia do not have counterparts in the peripheral nervous system. Appendable cells, check these puppies out. What kind of... what do they look like? I don't know, they look to me like simple cuboidal epithelium. What? What a coincidence, that's what they are. They're epithelial cells that line spaces like the central canal in the spinal cord and they produce cerebrospinal fluid, they barf out cerebrospinal fluid and they circulate it with these little cilia attachments that are waving around and moving the cerebrospinal fluid around. Cerebrospinal fluid, it's actually found in your brain and it's found all the way down into your spinal cord and it surrounds the whole, all those structures that circulate it from your brain to your spinal cord. And who's doing that? Your friendly little appendable cells. The other guys that are not found in the peripheral nervous system are your microglia. These guys are basically macrophages, which just means that it's an immune system cell that is kind of like an amoeba. They go around, they're called amylizing, very specific scientific term, just kidding. They go around yumturalizing or eating or phagocytizing substances in the environment. They're cleaners. They make sure that the crap doesn't stick around and all of these guys, what are they doing? They're supporting the neurons. They're like, the neurons are like the professional athletes and everybody else is a support team. The neurons are like the president of the United States and everybody else is like the security people and everything that goes with them. What are those people called? Security people and everything. The ones that do have counterparts in the peripheral nervous system. First of all, who's this guy and what do you think he's doing? What are you doing grabbing a hold of that axon and wrapping yourself around that axon? Make a dendrocytes, make myelin. And the myelin, this is fantastic. The myelin is literally wrapped cell membrane. That's how it ends up being fatty because it's cell membrane, which is a phospholipid. Fat, phospho, fat. The lipid part is the fat part, not the phospho part. But anyway, they wrap themselves around the neurons axon to create the myelin sheath. Yes, who is also doing that in the peripheral nervous system? The Schwann cells. They are different. They are structurally different. You can see that we haven't drawn them the same and that's cool. We'll just know that the oligodendrocytes and the Schwann cells carry out the same function just in different parts of the nervous system. The other guy, now this guy, I'm sorry, but I'm going to argue that this one possibly might be the most important glial cell and maybe the most important cell in the nervous system period. The astrocytes, I think of them as little mama cells. They actually surround the neuron cell body. They've got their hands on the neuron. Okay, they're not hands, but I think of them as hands. They've got little extensions of cell body that they wrap around the neuron. They actually wrap themselves around capillaries in the nervous system and create a second barrier between stuff that's in the blood, like poison that you put in there, like alcohol or drugs, and the neuron itself. So they're like this barrier between the blood and the neuron cells in your brain, also known as the blood-brain barrier. Those are the astrocytes who are doing that stuff. The protector, they claim they have... There's current research that's showing that they actually participate in communication. We think of just the neurons are the ones that are passing information back and forth, but there's an argument that no astrocytes are playing a role as well. There's an argument that the astrocytes are playing a role in telling the neurons where to create synapses with other neurons, where they're playing a role in directing traffic. Unbelievable. Their counterpart in the peripheral nervous system are the satellite cells. Now, we're going to see these. Does this... this is a neuron cell body right here. Does this kind of make you think of the ganglion? Yes, the satellite cells are protecting the cell bodies found in the ganglia. And so we'll actually see them in our slides today. Okay, now let's go talk about the histology that we're going to do in class.