Subcortical cerebrum

Voiceover: In this video, I'm going to talk about the subcortical cerebrum, the deep part of the cerebrum, when we look deep inside. Recall that the cerebrum is the top part of the brain here, and inside the cerebrum, we have both grey and white matter. I have a few different illustrations here, and there are some grey matter nuclei, and white matter. The entire cerebrum is covered with grey matter that we call cerebral cortex. These deep structures, like this deep white matter, and these deep grey matter nuclei, we call subcortical, beause they're deep to the cerebral cortex. They're beneath the cerebral cortex. I've got three very nice illustrations here to point out some of the structures that are subcortical structures of the cerebrum. To orient you, this illustration right here is looking from the front, just like my outline over here. Let me just draw an arrow over here. We're looking from the front, and we've cut down into the brain, so we're looking into the brain tissue. This illustration, this view from the front, is cut at one level here, and it's cut a little farther back over on this side. Over here, in this illustration, we're actually looking down from the top, so this is like if we've cut across the cerebrum like this, horizontally through the cerebrum, and we're looking down from the top. This is a top-down view, that's this guy over here. Let me just label that top. This one right here, we've actually cut down the middle, so we've cut down, if we're looking from the front here we've cut right down and we're separating the right and left, the right cerebral hemisphere from the left cerebral hemisphere. In this view we're actually looking at it from the right. We're looking at the middle from the right side. Let me just write that here, so I'll just write, we're looking from the right side, at the middle of the cerebrum, if we've divided the left and the right half. We're actually looking at the right side of the left cerebral hemisphere. As you can see from these illustrations, there's a lot of white matter deep in the cerebrum. This cerebral hemispheric white matter contains myelinated axons projecting to or from the cerebral cortex here on the outside of the cerebrum, and to and from these subcortical structures, like these grey nuclei deep in the cerebrum, and/or to and from the brainstem. Here we're seeing the brainstem down here, and all this white matter is connected. There's lots of names for different areas of this white matter. I'll just mention a couple of them. One important subcortical white matter structure deep in the cerebrum is this one right here. Let me color this in, this band of white matter that's going deep in the cerebrum, between some of these grey matter nuclei that are deep in the cerebrum. The name of this subcortical band of white matter is called the internal capsule. I'll write that right here. If we look at it on this illustration that's a top-down view, they've actually colored it in on this side, and tried to show how these axons are coursing out and connecting different areas of the cerebrum. Let me just color that in, it's this part right here. On these top-down views, it makes this V shape, it's kind of shaped like the letter V, and it separates some of these subcortical grey matter nuclei. The internal capsule contains a number of important pathways for information traveling around the central nervous system, including quite importantly, the corticospinal tract that contain the upper motor neurons, passes through the internal capsule. Several white matter structures connect the two cerebral hemispheres. I'll just mention the biggest one, which is right here. It's a big band of white matter connecting the right and the left cerebral hemisphere. You can see it over here, just part of it, in this top-down view as well. When we're looking at this view, where we've split the two cerebral hemispheres, it's this big band of white matter right here. Let me just color this in. This important connection between the right and the left cerebral hemispheres is called the corpus callosum. There are some other connections, but this is the biggest and the most important one, that allows information to travel from one cerebral hemisphere over to the other cerebral hemisphere, and vice versa. Several subcortical nuclei function as a unit, and so they're collectively called the basal ganglia. If we're looking from the front, these nuclei right here are part of the basal ganglia, as is this one right over here. If we're looking from the top, these nuclei right here are part of the basal ganglia, as is this one. There are some others as well, that aren't on these illustrations. Even though they're anatomically separated by white matter, like the internal capsule here, they function as a unit, so they're collectively called the basal ganglia. The basal ganglia play a major role in motor functions. They don't have upper motor neurons themselves, but they help out the motor areas of the cerebral cortex to perform proper movements. Some parts of the basal ganglia also contribute to cognition and emotion. So there's some cognitive and emotional functions that the basal ganglia also contribute to, in addition to their major role in motor functions. Another group of subcortical cerebral nuclei are collectively called the thalamus. The thalamus is sometimes also called the diencephalon, which is the name of the embryonic structure that it develops from. You might hear people using either name, thalamus or diencephalon. In this top-down view, all of these nuclei, this collection of nuclei right here, are the thalamus. If we look between the two hemispheres, the thalamus is right around here. It's just underneath this part of the brain right here. The thalamus plays a very important role in sensory functions, because almost all of the senses have pathways that travel to the thalamus, and there's sensory processing that occurs in the thalamus, and then they pass through the thalamus, on the way to areas of the cerebral cortex involved in those, doing more processing of those senses. But the thalamus is also very important for all of the higher functions of the brain, including cognition, emotion and consciousness, because the thalamus is connected to many, many brain areas. It plays a role in processing and passing information around from different areas of the cerebral cortex and other subcortical structures. The last collection of nuclei that I'll mention, although there are many more, is a group of nuclei that we collectively call the hypothalamus. It's called hypothalamus because it's right below the thalamus. The thalamus is around here, and this area right here is the hypothalamus. If we're looking at some of these other views like this top-down view, some of this would be part of the hypothalamus, because here they've drawn that they've cut deeper onto this side, so we're below the thalamus over here. The hypothalamus is connected to and controls this structure right here, which is called the pituitary gland. I'll just circle that right there. The pituitary is the master gland that plays a huge role in controlling all the other glands in the body. Our system of glands we call the endocrine system. The hypothalamus plays a major role in controlling and interacting with the endocrine system, and is really the link between the nervous system and the endocrine system. But in addition to this, like the thalamus, the hypothalamus is connected to many brain areas, and plays a role in many of the higher functions of the brain as well, including cognition, emotion, and consciousness. There are other subcortical nuclei that also have extensive interconnections with all sorts of different areas in the brain and are involved in many of the lower and higher functions of the brain, but I'll stop here, because I just want to introduce these structures that are deep down in the cerebrum which we call subcortical, so you can see where they stand in relation to the cerebral cortex on the outside of the cerebrum, and the brainstem below the cerebrum.