Organization of the Nervous System

by Jason Amores Sumpter
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hi. In this lesson, we'll talk about the structure and organization of the nervous system. Now the nervous system can be divided between the central nervous system and the peripheral nervous system. And the central nervous system is composed of the brain and spinal cord, and everything else is considered part of the peripheral nervous system. Now we often classify the tissue found here as being either gray matter or white matter, and that distinction is based upon whether or not the tissue mostly consist of neuron cell bodies or militated axons. Remember that Meilan is a fatty substance, coating the outside of axons and, just like fats, appear to the naked eye. When you look at a bunch of myelin ated axons, they just kind of look white from all the fat, whereas the cell bodies take on that gray appearance and you can see that in the brain. The outside of the brain, for the most part, is made up of gray. Matter can see it all along here, this darker stuff along the outside, that's all gray matter. Of course, there are some pockets within the brain as well. However, the general trend is that the gray matters on the outside, and the white matter is on the inside. All this business in here, that's all white matter. Now the organization in the spine is actually the opposite, whereas in the brain, the gray matters on the outside of the white matters on the inside, in the spine, which we're looking at here, this is the spine. You can see that the gray matter is actually found on the inside right, and the white matter is on the outside, and that's just a little pattern to take note of. It's not something that you need toe really stress about as being super important and related to a bunch of other stuff. Now, within the central nervous system, we often find bundles of axons traveling around together, and we call these tracks and make this distinction, because when we talk about bundled axons outside of the peripheral nervous system, we call them nerves. So you know, for our purposes, tracks nerves. Same difference. Really. We don't need to care too much about those distinctions, but I want to point out the difference in terminology. Now the brain and the spine are not actually solid masses. The brain has thes cavities called ventricles, and this is where the cerebrospinal fluid is produced. That's the fluid that actually bathes the brain and the spine. The spine itself, although you can't really see it in this picture, has a teeny little hole in it. And this is called the Central Canal. It's just a hollow tube that runs through the spine, so the the central nervous system is obviously an incredibly important structure. It is the command center of the body. As such, it kind of needs to be isolated. You know, you often get toxins, pathogens, all that bad stuff in your body, right? That's what your immune systems for. That's what your livers for. That's what your kidneys air for. Get that stuff out of there. However, the central nervous system is too important to be compromised, so it's actually gated from the rest of the body by what's known as the blood brain barrier. This is an end Athena Liam barrier that is composed of Astra sites, which are a type of glide all cell, and it's going to separate the extra cellular fluid of the central nervous system that is the fluid around the brain and spinal cord from the blood and you can see this right here. These cells are all Astra sites, and you can see that they are, uh, kind of like glue ping around this blood vessel. You can see the red blood cells right there. They're glue ping around it to create a barrier. So the blood brain barrier isn't so much like one wall in one location. It kind of is a structure that is very diffuse, but it's super important. And it's importance comes from the fact that the central nervous system has to be very, very carefully regulated. And we don't want toxins, pathogens, any of that stuff getting in, if it all possible now, the peripheral nervous system extends throughout the body, and it's made up of nerves which remember acts on bundles and ganglia, which are clusters of cell bodies outside of the brain and the spinal cord so similar to how in the brain, the cell bodies of neurons group together in the gray matter. Likewise, in the peripheral nervous system, you often see the cell bodies of neurons grouping together and sending their axons together as bundles. And you can see here everything in blue is part of the peripheral nervous system. The spine and the brain are kind of yellowish color. Uh, and all the other stuff is the peripheral nervous system on. You can see it's it's very diffuse. Network goes all throughout the body Now the other thing I want to point out is here We're looking at a section of the spine. Very similar Thio. This one right here. It's just not as good a picture. But what I want to point out to you is this ganglion. There are ganglia, riches, the plural of ganglion that run along the side of the spine. These air actually known as dorsal root ganglion. They're not the only gangly of the peripheral nervous system, but they're very important one, and I want to just point them out. And, of course, over here these are nerves that will connect to the spine, and you can see that there are a variety of ganglia and our ganglia there. So with that, let's go ahead and flip the page