[MUSIC] Okay, welcome to neuroanatomy, a week on neuroanatomy. And we're going to look at neuroanatomy in three modules. We're going to start with development because understanding how the nervous system develops is incredibly helpful for understanding the, the eventual, very complicated structure of the brain. And then we're going to look at the neuroanatomy and the regional functional anatomy of, of the nervous system. And finally, we're going to look at lesions, what can go wrong. Most notably, we'll look at strokes and how they, how they happen, and the blood supply to the brain. Okay, so we're going to start with development. And we're going to start with happy birthday to the nervous system. The bir, the nervous system is going to get born at around 15-to-20 days of gestation. At this point, at the beginning of this point, the, the embryo is a few dozen cells, and it's divided into these three layers, the ectoderm, the mesoderm, and the endoderm. And we're going to concentrate on this outer layer, the ectoderm, because that is going to become the nervous system and the skin. And that's really interesting and it's important and we'll see, we'll come back to that. Because they, because the nervous system and the skin share a developmental origin, there are disorders that happen that involve both skin and nervous system effects. Okay, so around 15-to-20 days, at, at this point a piece of this neuroectoderm become, of this ectoderm becomes special. And it turns into what we call neuroectoderm. And the neuroectoderm is going to form the entire nervous system. It's going to do that in two parts. We're going to separately form the central nervous system and the peripheral nervous system. The central part of this neuroectoderm, this piece here, is going to go off and become the central nervous system, which is the spinal cord and the brain. And then, these wings here, these part, this part of the neuroectoderm actually contains these migratory cells. These are, are cells on the march, they are going places. They go all over the body. And so they are actually are going to form the peripheral nervous system. So the peripheral nervous system is formed by the migratory cells out here which are called neural crest cells, okay. So, let's just look at that in situ. So the, neural tube is going to form the brain and the spinal cord. And the neural crest, I'm going to reverse my colors here, neural crest is going to form three different types of cells, sensory cells, that sit out here and send information into the central nervous system. So the second part of the peripheral nervous system are these autonomic ganglia neurons. And these are neurons that innervate things like sweat glands and hair follicles and the heart, and the the air ways, the, the lung, the bronchi. And do things that we're not in conscious control of, such as sweating, piloerection, speeding up our heart rate or slowing down our heart rate. And these all come from the autonomic ganglia. And we'll look at them a bit more later. And the third piece of the peripheral nervous system is called the enteric nervous system. We're going to look at that in the next slide. So the enteric nervous system actually lines the gut from the esophagus all the way down through the colon. And this is responsible for the automatic movement of the contents of the gastrointestinal tract through the entirety of that tract from from your esophagus out until you void feces. And so in situations where there is no enteric nervous system, or more commonly where there is a reduced number neurons in the enteric nervous system. This typically happens at birth a, a newborn will be born with something called megacolon, which is exactly what it sounds like. It means that the colon is really big because it contains a lot of feces that have not been pushed out. This has to be corrected. And this is a piece of the enteric nervous system. And just to show you, so on a, on a person, the enteric nervous system is lining the ens, esophagus down through the stomach, through the intestines, through the large intest, testine, and out through the colon. That entire length of the GI tract is, is lined with the enteric nervous system. Okay. So, one of the amazing features about neural crest is that it's not devoted only to the nervous system. It also produces many other tissues that are non-neural. So for example, the pigment-containing cells that, that you have, both in your skin and in your hair these are called melanocytes, they, they give you coloring. It, neural crest is also responsible for producing your cornea, for your aorta for the meninges that cover the brain. And it's also, it doesn't become, but it is needed, it's absolutely required for the correct development of teeth, for the the bones and the muscles in the face, and for the inner ear. So, if there is a problem with the neural crest, the result will be a combination of both neural and non-neural problems. And the, the best example of that is a syndrome called Waardenburg syndrome. And this shows a, a young girl with this syndrome. It is neural crest disease. And she's very likely deaf. We can't tell that by looking at her but Waardenburg syndrome comes with deafness because the inner ear does not develop correctly. You can see other aspects of it. She has this abnormal pigmenting in her hair. She probably also has it on parts, parts of her body and her skin. She also has blue eyes, Waardenburg syndrome patients have blue eyes. And you can see that there's a a particular appearance to the, to the face. The eyes are, are very far the inner parts of the eyes are, are far apart, leading to a very broad bridge of the nose. And, and they're, and this person may also have megacolon. There are a variety of other symptoms that can accompany this. Okay. So, that's our, our short introduction into how we get a peripheral nervous system. And now what we're going to do its turn our attention to the development of central nervous system. [MUSIC]
