Okay, so this is a tutorial on the parts of the brain. This is a basic tutorial and I want to give you an overview of the different parts that make up the brain. there's not going to be huge amounts of detail here, but this is just a tutorial to sort of orientate yourself with regard to structures of the brain.
We’ll start off by looking at the brain stem. First of all, I'll just point out what we're looking at here. We're looking at a side view of the brain. Anterior is this side, posterior is this side, and obviously superior and inferior. You can sort of see the veins and how it sits there.
I'm just going to rotate it around and we'll take a look at the brain stem. I've just removed some of the nerves to make it a bit more clearer. The brain stem is this bit here and it consists of three parts. You've got the medulla oblongata, the pons, and the midbrain. The medulla oblongata is this bit here, which is most distal or most inferior, and it starts at the end of the pons and it ends where the spinal cord begins. The spinal cord begins at the opening of the skull at the foramen magnum, and this is where the medulla oblongata ends.
Just above it you've got the pons, which is this bit here. And above the pons, you've got the midbrain. What I'm going to do is just isolate the brain stem. I've just removed all the other structures. We're looking at the exact same view. You've got the medulla at the bottom; the pons and the midbrain above it.
The midbrain is this region here and it consists of -- so, at the front, you've got these bits, which are called cerebral peduncles and, at the back, you've got these little sort of hills, and these are called the corpora quadrigemina, and this is Latin for quadruplet bodies because obviously there's four little bumps.
The top ones are called superior colliculi and the bottom two are called inferior colliculi. And the word colliculi is Latin for lower hills, because of their appearance. These colliculi sit on the tectum, so the tectum is sort of the roof of the midbrain. So, tectum means roof in Latin, so here corpora quadrigemina sit on the tectum of the midbrain.
The midbrain is this structure here. You've got the cerebral peduncles and you've got the tectum with the four colliculi. In the midbrain, you've got loads of nuclei. So, nuclei are collections of cell bodies, which are contained in the nervous system. Sorry, in the central nervous system, whereas ganglia are collections of cell bodies in the peripheral nervous system. In the brain stem, there's lots of nuclei, which are important for controlling functions like heart rate and blood pressure and respiration as well as things like the level of consciousness and wakefulness and arousal. And then you've got lots of cranial nerve nuclei and nuclei related to the cerebellum, which I'm just about to show you.
I've just switched back to this model and I'll just show the cerebellum. The cerebellum is this part of the brain, which sits behind the brain stem. You can see it here, sitting directly behind the brain stem, and you can see it has these two lobes. The cerebellum means little brain in Latin, and this has loads of connections with the brain stem and it's important in motor control and coordination and balance and muscle tone, and that sort of thing.
If I remove the cerebellum, and I'll just remove the hemispheres as well. We can see the midbrain here, you can identify them by the colliculi. That's the midbrain sitting. Well, this is the dorsal surface of the brain stem.
The next part of the brain that we need to talk about is called the diencephalon, and this is the part of the brain that sits on top of the midbrain and it consists of the thalamus, the hypothalamus, and the pineal body or the pineal gland, which is what it's also called. I've just removed the cerebral hemispheres and the cerebellum, and we're looking at the back of the brain stem. Remember, you can see the midbrain here, which is easy to notice, and then, below, you've got the pons and the medulla oblongata. The midbrain is sitting just above this.
You can see this paired structure. These paired sort of oval roundish structures. These are called the thalami, and you've got two thalami. One on each side, and they're joined at the middle via the interthalamic adhesion. Just below the thalamus you've got the hypothalamus, which is a little bit smaller. The hypothalamus sits here. I just got rid of a few of these structures so you could see the oval-shaped thalamus and the hypothalamus below it. And at the back, just here, you've got the pineal gland.
The thalamus is a really important structure to know about because it essentially acts as a switchboard or gateway to the cerebral hemisphere, so it relays connections to the cerebral hemisphere - to the cerebral cortex of the cerebral hemispheres. And it contains lots of nuclei. The thalamus sends and receives fibers from the cortex and it's got thalamo-cortical loops and lots of reciprocal connections. It's important for many things such as sleep and wakefulness. It's important in coordinating information from the various sensory systems and it also has links to the basal ganglia, which I'll come to talk about, and also the cerebellum.
I've just switched to this lateral view. I've removed various structures so you can visualize the thalamus right in the center very clearly. You get a lot of fibers projecting into the thalamus and the thalamus coordinates all this information and it projects fibers into the cortex and it also receives fibers back from the cortex. You’ll often hear the thalamus referred to as a relay or switchboard or a gateway for this reason.
The cerebral hemispheres are what most people think of when they think of the brain. We're looking at these two cerebral hemispheres here. You've got a right and a left cerebral hemisphere. And the cerebral hemisphere is responsible for higher functions. So, thinking, memory, consciousness, language, emotion, movement, and sensory perception - these kinds of things. The cerebral hemisphere consists of an outer cortex, which is made up of six layers of gray matter, and you've got the inner portion of the cerebral hemisphere, which is made up of white matter.
I'm just going to rotate the brain around and I'm going to switch to a diagram to illustrate the cerebral cortex. So if we take a… imagine just cutting the brain through this axis here. So, directly -- we're going to take a slice of the brain down here.
We’re looking at this cross section of the slice we've just taken, so this is a coronal section. And what I wanted to show you on this slice is the cerebral cortex. The cortex is the outer part of the cerebrum and it is gray matter. You can see this thin bit on the edge of the cerebrum. This is the cerebral cortex and it consists of up to six layers of neural tissue.
The neocortex is where the cortex has six layers. Any other parts with less than six layers is referred to as the allocortex. And this allocortex can be subdivided into an archicortex and a paleocortex, so these are part of the cortex with less than six layers. The neocortex is the one to remember because this is the newer, sort of evolutionarily newer, part of the cortex and is responsible for higher functions like language and conscious thought. So the neocortex has six layers.
Gyri and Sulci
Just looking at the outside of the cerebral hemisphere, you can see that there are these grooves and you've got ridges. The ridges are called gyri and the grooves are called sulci. And you've got lots of these different grooves and ridges, as you can see, and they all have different names. But two important ones to remember are the central sulcus, which I'm showing you here with the arrow, and the lateral sulcus. And I'll do another tutorial, which goes through all these different grooves and ridges.
Lobes of the Brain
But the reason I showed you these - the two sulci, the central sulcus and the lateral sulcus - is because these two sulci can be used to separate some functionally important lobes of the brain. you've got four lobes of the brain, which are separated by various grooves.
Anterior to the central sulcus, which I'm drawing along here, you've got the frontal lobe because it sits behind the frontal bone of the skull. This is the frontal lobe that I've outlined in red. Posterior to the central sulcus, you've got the parietal lobe, and this runs like this, so I'm outlining this in yellow. And this is called the parietal lobe because it lies under the parietal bone. And inferior to the lateral sulcus, which I'm drawing on in green, we've got the temporal lobe. I'm just outlining the temporal lobe here, and it runs like that. And right at the back we've got this lobe here, called the occipital lobe, which I've just outlined in blue.
This is quite a rough illustration of the four lobes, but I wanted to show you how the central sulcus and the lateral sulcus are important and defining these different areas. Anterior to the central sulcus, you've got the front lobe; posterior to it, you've got the parietal lobe. And then you've got the lateral sulcus, which, inferior to the lateral sulcus, you've got the temporal lobe.
The frontal lobe is important in decision making, problem solving, and planning. The temporal lobe is important in memory, language, emotion, and hearing. And the parietal lobe acts as sort of integrator of sensory information, so it receives and processes sensory information and the occipital lobe, sitting at the back, is responsible for vision.
That's a very crude overview of their functions, but it gives you an idea that different lobes have different functions.
The cerebral hemispheres cover a lot of other stuff that's contained within the brain. you can't see here, the midbrain or the diencephalon, which I showed you, but there are also other things contained - other structures in the brain, which we need to know about.
I'll just remove the cerebral hemispheres. What we're looking at now is some of the stuff that's contained within the hemispheres. I'll just show you what I did here. we're looking lateral view of the brain. We've got the cerebral hemispheres, we've got our cerebellum, and we can see the medulla and the pons from this lateral view.
I'll remove the left cerebral hemisphere and we've got these structures that are contained within it. You can see that the hemisphere was here and I've removed it, and we're looking at these structures inside the brain. I'll get rid of that one as well. I'll just show you some familiar structures. You can see the thalamus on either side, the thalami. You can see the hypothalamus. And if I remove the cerebellum, you can see the midbrain with the colliculi sitting on the tectum.
What we've got inside, contained in the hemispheres, are basal ganglia, the limbic system, and ventricles. We’ll take a look at the basal ganglia first. we'll actually use this model with one-half of the cerebral hemisphere because it's a bit easier to orientate yourself when you can see the hemisphere.
The basal ganglia - the term is actually a bit of a misnomer. It should be basal nuclei because these are collections of cell bodies, which are contained in white matter in the central nervous system. they should be called nuclei rather than ganglia, but they're called basal ganglia, so we'll stick with that.
You’ve got three parts to the basal ganglia. You've got the caudate nucleus, which is this structure here. you can see here it's got three parts. It's got a head, a body, and a tail, which winds around like this. that's the caudate nucleus. And then, outside the caudate nucleus, you've got the putamen. So this is this round, curved structure. this is the putamen. And just sitting medial to the putamen, you've got the globus pallidus.
I've just faded away the various structures, so you can see the globus pallidus, which has an internal and external or lateral and media part. So the globus pallidus is these two structures. The lateral and the medial globus pallidus. these structures sit medial to the putamen.
Collectively, the globus pallidus and the putamen are referred to as the lentiform nucleus or the lenticular nucleus. And the caudate nucleus, which is this structure with the head, the body, and the tail that winds around, combined with the putamen, is called the neostriatum. you've got these structures on both sides. If I just rotate around to the other side, you can see the c-shaped caudate nucleus. you can see its head, the body, and the tail, you can see the putamen sitting laterally, and you can see the globus pallidus with its lateral and medial parts sitting medially.
And from this anterior view, which we're now looking at, you can our see structures from the diencephalon - the thalami. these sit medial to the globus pallidus. There are also two other components of the basal ganglia, which are the subthalamic nucleus and the substantia nigra, which I'll show you another tutorial.
The next part is the limbic system, which is quite complicated because it's not actually an anatomically distinct set of structures. It's not very clearly defined. It's more a collection of functionally related nuclei and cortical areas, but there are few structures that are worth pointing out.
We’ve got the hippocampus here, or the hippocampal formation, and this structure is important in the formation of memory. this structure actually sits medially in the temporal lobe. if I just rotate around, you could see the temporal lobe here and it sits within the medial aspect of the temporal lobe. And then you've got the fornix. if I just remove the basal ganglia and the lateral ventricle -- so the fornix runs up like this. You can see it here. And you've got the mammillary bodies down here.
And if we follow the caudate nucleus around - follow the head, body, and the tail -, at the end we've got this walnut-shaped structure, which is called the amygdala or amygdaloid body. This is often included by definition with the basal ganglia, but it's part of the limbic system. So those are just a few parts of the limbic system, which are worth pointing out, but it's a lot more complicated than that.
Finally we've got the ventricles. The ventricles are these gray parts of this model. You’ve probably been wondering what these are, but these -- I’ll just rotate it on the right. These are the ventricles. And the ventricles are developed from the neural tube and are remnants of the neutral tube, and they're filled with cerebrospinal fluid, which is a colorless fluid, which protects and nourishes the neural tissue.
I've just switched to a diagram of the ventricular system of the brain. you can see there are the C-shaped ventricles on either side, so these are the lateral ventricles. You've got one on either side and they connect to a third ventricle, which sits in the midline, and they're connected to the third ventricle by interventricular foramina, so these little bits on either side. And then the third ventricle connects to the fourth ventricle, which lies within the pons.
You can see the ventricles in relation to these other structures and you can see the third ventricle in the midline. And the walls of the third ventricle are made; are supported by the thalamus. They're made up by the walls of the thalamus. And the cerebral aqueduct runs within the midbrain to connect to the fourth ventricle.
If I just rotate this around; remove the cerebellum. You can see the fourth ventricle here, sitting within the pons. if I just fade out the -- very slowly, you can see the cerebral aqueduct connecting the third ventricle to the fourth ventricle like that.
Those are the parts of the brain. we've gone through the brainstem, the cerebellum, the diencephalon, which consist of the thalamus, hypothalamus, and pineal body. We've talked about the cerebral hemispheres and the cerebral cortex. We've talked about the lobes and we've talked about the stuff that's contained inside the hemispheres - the basal ganglia, the limbic system, and the ventricles. I hope that's given you a sort of three-dimensional idea of how the parts of the brain relate to each other.