[MUSIC] Okay. We have a tube. The tube is going to make the whole central nervous system. Back in the spinal cord, the tube becomes the spinal cord. There's not much difference between the tube and the spinal cord. It's a pretty simple thing. But a tube also becomes the brain, and it does that through a series of steps that we're going to examine. So there's just a simple tube is going to become this incredibly convoluted and complex brain. Okay, and the way that this happens is that at the front of the neural tube the place where it's going to be within the skull, with in the cranium there are three swellings, there are swellings. These are called vesicles, and the brain vesicles are going to become the bran. At the beginning there are only three of them. And so, what I've shown you here is the three vesicle stage. Back here is the tube that's going to become the spinal cord, and we're going to now, that's the last I'm going to say about the spinal cord. We're going to concentrate on this part of the neural tube that has swellings that's going to become the brain. And there are three swellings. The hind brain, the mid brain, and the fore brain. So the hind brain's next to the spinal cord, the mid brain is in the middle, and the fore brain is up and the closest, It's the most interior the farthest to the front. Very quickly the three vesicle stage has one more split. Which is at the fore brain vesicles split's into two vesicles. One is called diencephalon and one is called telencephalon. These are names for the vesicles swelling, for these swellings. They're not common English terms and unfortunately there are no common English terms that are in wide use for these two vesicles. So we're going to stick with telencephalon and diencephalon. Back in 1800 some people, term this the telencephalon the end brain and the diencephalon the interbrain. Unfortunately those nice terms are not in common usage. The diencephalon is going to become the thalamus and the hypothalamus. The telencephalon is going to become the cerebral cortex, the core parts of the basal ganglia and the amygdala. And a few other structures. So what we're going to concentrate on now is what happens to the telencephalon and the diencephalon. So once the telencephalon forms, it almost immediately invaginates, and it invaginates to make two different swellings that are actually separated across the midline. So here's the midline, we're looking down on the embryo on the brain and what you see is that there's this. This is the telencephalic hemisphere, and this is the telencephalic hemisphere. There's a left and right hemisphere. This can become the left and right hemisphere of the brain. So this happens almost immediately. And so what you have is the tube, which was like this, is now become a y. Here's the tube with the diencephalon. The midbrain, the hindbrain. Back here is the spinal cord. And up here, are the two telencephalon hemispheres. The right and the left. Okay. Now, we're going to look at one more thing which is really quite remarkable, from the diencephalon, there's an outpouching. Now, all of this, everything except for this outpouching is contained in what's called the cranium and the cranium is the vault within the skull. It's not the entire skull. It's that container where the brain goes. That's called the cranium. And what we're going to do now is look down on the bottom of the cranial cavity. So here we are. This is the front. This is the back. This is a skull. This is the foramen magnum. Down there is the spinal cord. Up here is the brain. You can see that the temporal lobe would sit right there. And right here, I don't know if you can see it, but there are two convexities. And these convexities are the top of the globe of the eye, so right here sits the two eyes. The diencephalon is sitting right about here, and that out pouching that I just showed you Is going to go out this hole and it's going to form a cup. And that is the retina. So the out pouching forms what's called the optic nerve and the retina. That out patching in the embryonic stage is called the optic vesicle. But in the adult it's going to form the retina and the optic nerve. So that's really amazing. Why is that amazing? Because what you have is an accessible piece of the central nervous system. This is central nervous system, it comes from the diencephalon, it is continuous with the diencephalon. Here's the diencephalon, and here's the optic nerve, here's the retina. It's all contains within the same meninges. It's all surrounded by CSF. So it's one that means that when you look in to somebody's eye you're looking into the central nervous system. You're not looking to the brain. But it's a window on the brain, whatever is happening inside the cranium? Can be reflected out here in the eye, so that let's say and this is how looking into the eye is commonly incredibly useful. Let's say that somebody has a stroke or tumor that has increased pressure in their brain. Now when you look into the eye you're going to see signs of that increase in pressure in the eye. And that is shown actually not increased pressure but the normal view of a retina is shown right here. And so when you look at, when you, when a. When a person with an optomoscope looks into the eye and sees the retina, they're seeing the central nervous system. That's pretty awesome. Really cheap way to image the central nervous system. Okay. Great. So in the next segment what we're going to do is we're going to look at how the brain expands into all of it's convolutions. [MUSIC]
