[MUSIC] Okay. So when we left off in the last segment, we had four vesicles. We had the hind brain, the mid-brain, the diencephalon, and then we had this huge expanded telencephalon that has stretched over and done the combover on top of them. And that's kind of how we left it, so let's just look at this. This is looking from the side, this is the front, and this is the back. The spinal cord, the hind brain, the mid-brain, the diencephalon, and this is one telencephalic hemisphere. And nothing's particularly joined to each other. Now, we're just going to take an imaginary slice, right through here. And if this were all that there was, this is what it would look like. You'd have the diencephalon, as a little island in between these two large hemispheres. That's not what the brain looks like when it's an adult, because there are two tracks that develop after this. And one joins the two hemispheres. And this track is called the corpus callosum. Your left and your right cerebral hemispheres, slightly different. They have different emphases, different tendencies, and they get along basically by communicating through the corpus callosum. The second thing that happens is that we join the telencephalon to the diencephalon, with two big tracks that look like this, that come down in here. And these are the internal capsules. [SOUND] And these carry information. One of the important things that these carry is motor information, going to the motor neurons. So Simon says, move your hand. That information comes down from the motor cortex, travels through the internal capsule, crosses when it gets to the spinal cord, and then goes down to talk to a motor neuron on the other side. So in that way, your left hemisphere will control your right muscles, your right hemisphere will control your left muscles through the motor neurons. So this internal capsule carries this tract, which is called the corticospinal tract. [SOUND] It carries the corticospinal tract, and it carries a bunch of other tracts that go down. So, for instance, to move your face, the muscles of your face. And so these are very important tracts. But for the purposes of right now, the thing to remember is that they mean that the brain now is one, it doesn't have islands. It's one piece of tissue. One piece of continuous, it's continuous from side to side. There is this empty space in here, and what's kind of interesting about that is that what's in here is not brain. It's inside the cranium, it's inside this cavity of the skull, but it's not brain. What it is is mostly veins and arteries, and there can be an accident and one of them can open up and have a bleed, in which case a neurosurgeon needs to come down here, and access this space. This space deep within the cranium that does not contain brain. So let's just go over here, and we'll just take a look at some of these things. This is now looking at a brain from the back. Here is the cerebellum. You see the cerebellum? You see the, this is the right hemisphere, this is the left hemisphere, these are my hands, and down here, right here is, this is all white. And this is the corpus callosum, containing axons that are going right across between the hemispheres. And they join the two hemispheres, and they make us appear as though our hemispheres are getting along well, because they communicate. Okay, and let's just take another view of that here. In the next view, what we're going to do is we're going to cut right here. That's called a midsagittal cut. And then we're going to look from the side at this half of the brain. So that looks, this. We're actually looking at the left side of the brain. And what you see is, I'm going to remind you that this is all telencephalon. This is all cerebral cortex around here. This piece right here is the corpus callosum, this is the corpus callosum. And this is joining the two hemispheres. This is joining this hemisphere with the hemisphere that we've just cut off. And just to remind you, here's the hindbrain, here's the midbrain, and this is the diencephalon. Okay. Just a couple more pictures to show you. So here, what we've done is we've cut sagittally, but not in the middle. It's not a midsaggital cut. It's a parasagittal cut, it's off to the side. And that enables us to see this piece right here, which is the internal capsule. This is the internal capsule. This is joining the telencephalon to the diencephalon. Here is one final view of this. This is now a horizontal cut, like this. Here is the front, here is the back. This is a piece of the corpus callosum. It comes around like this, and it's been cut in two places, and this is the internal capsule. So in here is diencephalon, and everything outside of the internal capsule, this is all telencephalon, telencephalon, telencephalon. The final thing I want to do is to show you how we can now take this very complicated folded over structure, and flatten it into a diagram that we can use more simply than showing all this complicated anatomy all the time. And so, this shows you that here's the spinal cord. It's the spinal cord. This part, the pons, medulla, and cerebellum is the hindbrain. Here's the midbrain. Here is the diencephalon and this is the telencephalon. And what you can see is that we've joined the telencephalon into diencephalon with two internal capsules. And we've joined the two hemispheres to each other, using the corpus callosum. And this is a diagram that we're going to reuse over and over again. So, just to reiterate this is the internal capsule. This is the corpus callosum. This is the other side internal capsule. Okay, great. [MUSIC]
