[MUSIC] Okay, so we're going to now figure out how we can get from this plate of neuroectoderm, to a nervous system. And the central nervous system has to go from the caudal end of the spinal cord about here in an adult, all the way to the front of the brain. And this is a complicated thing, and how are you going to make the plate into this the central nervous system? Well, the strategy that is used is that we make a tube. So we make a tube that stretches from the back end of the spinal cord to the very front end of the brain. So here is an overview of where we're going. This is making the neural tube, here's the neural plate, this is neuroectoderm. And the central portion of it folds up, and then it actually folds and closes and becomes a tube. And then that buds off and now we have a tube from the front end of the central nervous system to the tip of the spinal cord, the back end of the central nervous system. So what's folding up is the central portion of the neuoectoderm. Now let's go to the board, and remember that neuroectoderm has two parts. It has this central part that's going to become the neural tube and then these two side wings that are the neural crests. Neural tube is going to become central nervous system. Neural crest is going to become peripheral nervous system plus a lot of other stuff like melanocytes. Remember Waardenburg syndrome? Okay, so this is the situation when at about day 21. And by the end of day 21 we already have this invagination and by the end of the fourth week by day 28, we're going to have a tube that stretches from one end to the other. And the way this works is that this tube, or this flat plate of neuroectoderm invaginates, it folds in, you can call this the neural fold. Some people call it the neural groove, really doesn't matter what you call it, it's a folding in. And then that increases until you have almost a tube, people will call this an omega shape, and then that does in fact become a tube. So here's the tube, here are the neural crest cells, they're on the wings of either side. And here is overlying skin and there's going to be muscle and bone in here. So after the tube forms, other tissues have to come in and cover the nervous system, that's important. We don't want our nervous system to be exposed. This whole process takes a week. And the way that it works, is that if we look down, now we're looking down at the length of the embryo, this is the front, this is the back. And around here, which is where the neck of the adult will be, this will become the neck region. Around here the neural tube first closes up so it's folding, it's folding. Where's the first place where it touches and becomes a tube? Right here, and from that one point it will zip. It'll zip up and then it will zip down. It'll zip up and then there's another point up here which starts to close and where these meet, there's one last opening where they meet. And that's called a neuropore, a neuropore. You have it right here, okay? So that's the anterior neuropore, the one in the front is the anterior neuropore, the one in the back is the posterior neuropore. These two are the last places that have to bud off. It's a little bit of a problem, it's little bit difficult and what we're going to see in the next segment is that it doesn't always work. But when the neural tube closure works correctly, what we get is a long tube from the sacral cord of the spinal cord. From the very back end of the spinal cord where your tail would be if you had a tail, all the way to the front of the nervous system to the front of the brain. Okay, so next we're going to look at what can, unfortunately, go wrong. [MUSIC]
