So now that we have discussed, remember that we're on the cerebrum. Remember, we're discussing the cerebral cortex, just that ribbon of gray matter that is the most superficial part of the cerebrum. And now we're going to be discussing the next part of the functional areas or the next category of functional areas, which are the motor areas. All of this stuff in red, which you'll notice is actually not that large a part of the brain. It turns out that movement is very important.
It takes up a big part of the cerebral cortex. However, it doesn't take up hardly as much, not even like a half as much space as all that. that sensory stuff.
But movement nonetheless is important. So we are going to be looking first of all at the primary motor cortex. The primary motor cortex is just this one gyrus. It's also called the precentral gyrus because it is just anterior to the central sulcus. So this is a bump.
It goes from side to side. It makes a headband. We're only looking at one side here. We're only looking at the left side. But remember that there will be a mirror image on the other side, which is the right side.
side of the brain. The primary motor cortex is responsible for conscious control of precise, skilled, voluntary movements. This is the part of the brain that the surgeons will look to when they're trying to, for example, allow a tetraplegic individual to have some amount of movement given back to them. They will be planting those electrodes directly on the primary motor cortex. So how do they know where to go?
This figure in your book, which is figure 12.7, is going to be the first one. going to give you a good idea. This is called a motor homunculus. Now on this side is the motor homunculus, on this side is the sensory homunculus.
This is a very unfortunate figure. I really wish they would separate these out because I think it can be confusing. So I'm just going to go ahead and block the sensory part of it because I want you to keep in mind that this is the motor side, however it does extend all the way to the other side and is a mirror image on the other side. Okay, so I hope you understand what I'm saying, is that if you had, it looks as though, oh, okay, this strip of brain, this side is responsible for the motor movement, and then the other side is responsible for sensation. That is not true.
Sensation. The primary somatosensory cortex, which we'll talk about in the next video, is the postcentral gyrus. We're talking about the precentral gyrus, which does extend all the way from left to right.
So we have a mirror image on both sides. on both sides. Okay, so when we look at this, what you'll notice is that there are representations on the primary motor cortex for different parts of your body. Lips, face, eye.
You notice that the lips take up a great deal of the space. of space. The tongue has its own little portion of the motor cortex, the primary motor cortex.
The thumb is very important. The fingers are very important. So they take up a great deal of space here.
A great deal of the architecture of the primary motor cortex will be responsible for just the movement of one little finger. It's very important then. We understand that. However, things like the entire arm will only have a small representation. representation on the primary motor cortex because the movement of the arm, of course, is very important, but precise movement of the arm is not important.
So you need to be able to move your arm, but do you need to move it precisely? Not really. So the entire trunk, the entire hip will only have small representation, the knee, the foot, even the toes do not have great representation.
The genitals, movement of the genitals is actually not that complicated and therefore it does not have a great deal of representation. However, it does have a lot of sensation. So the other side of it is going to be well represented.
So movement is not as important as sensation in the genitals. Okay, so I think that's what I wanted to say about this. So if you were a surgeon coming along and trying to hook up an electrode in a way that allowed a person to move their arm, basically you know generally where that person's arm is represented because everybody's arm is represented in about the same way. Now, will there be some variability from one person to the other? Yes, that is why these surgeons have to map out and kind of test things out and make sure that they're moving the right place, moving the right area.
However, you know, they can basically train the machine. and then move the electrode into more appropriate areas that allow for the movement that they want. So hopefully that makes sense.
So this is our primary motor cortex. Just anterior to the primary motor cortex and taking up more space is called the premotor cortex. So the premotor cortex is basically what we call an association area for the primary motor cortex. We're going to show this pattern where we're going to have a primary area and then an association area.
So movements will go through the primary area, but the primary thing will go through the primary area. but there will oftentimes be an association area that helps you to get a better quality of that thing. So in this case, we're talking about movements of different parts of the body. How do we move them? Well, we go through the primary motor cortex to move them, but if we want a more qualitative way to control those parts, then we're going to be turning to the premotor cortex.
So the premotor cortex is responsible for learned, repetitious, or patterned motor skills. The premotor cortex coordinates simultaneous or sequential actions, and it's also responsible for the planning of movements. Additionally, inside of the premotor cortex, we have a very important type of memory, which is called procedural memory. Most of the memory that we think of as memory is declarative memory. However, there's a certain amount of memory of movement that we have, we oftentimes will call this muscle memory, and that is actually stored here in the brain in the premotor cortex.
So if we remember how to tie your shoes without even thinking about it, then that is the responsibility of the premotor cortex. Yes, the movement of those fingers goes to the primary motor cortex, but the storage of which neurons to move in which sequential order will go through the premotor cortex. The next part of the movement, the motor areas that we're going to be looking at, is called Broca's area.
Broca's area is here, is here in this dotted line here. This is only going to be found in one hemisphere, usually the left hemisphere. This directs the actions of the tongue.
This directs the muscles of the tongue involved in speech. You can see that it is a massive area. It turns out speech is very important to humans. No surprise here.
The speech is very important. It allows us to communicate with each other, which is probably the most powerful thing that we do as humans, is to be able to communicate with each other. So a huge architecture, a huge amount of our cerebral cortex is devoted just to allowing the movements of our mouth when we are speaking. The last motor area we're going to be looking at is right...
up in this area here. This is called the frontal eye field. The frontal eye field, you may mistake this for vision.
It is not vision. This is a movement. This is not receiving any kind of information about light or color or anything like that. Rather, it is directing the voluntary movements of the eye.
This is responsible for things like psychotic movement or smooth tracking. We'll do a little very short experiment in class showing how psychotic movements work versus smooth tracking movements. But so the frontal eye field is a fairly substantial part of the brain considering that the only thing it does is moves the eyeballs.
It basically allows the eyes to move in a way that allows us to see something better. Like if you want to turn your eyes, if you want to... Move your eyes to look at something. That is the responsibility of the frontal eye field. Interestingly, that is very far separated from the visual cortex, which is responsible for actually perceiving vision, which is way back in here.
So the frontal eye field is the movement of the eyes. The visual cortex way back here in the sensory cortex allows us to actually perceive sight.