What’s up. Meditay here. Let’s continue the anatomy of the Central Nervous System.
In this segment, we’ll cover the anatomy of the Cerebral Cortex, which is what we call the external Telencephalon. So remember, the central nervous system consists of two parts: the encephalon and the spinal cord. The encephalon is then further divided into specific parts.
We have the brainstem, which consists of the medulla, pons, and the midbrain or the mesencephalon. We have the cerebellum back here, then the diencephalon and the Telencephalon. Our focus in this video is going to be the telencephalon, which is this blue part here.
But If we change this picture into a little more realistic one, we’ll find the spinal cord, the medulla, pons, and the Cerebellum. And then the Telencephalon would be the whole blue area right here. Let’s now make a vertical section just like this, cut it, and then look at the brain from this perspective.
We’ll see this. SO this is what we call a coronal section of the brain, and what we can see here is Pons and the Midbrain, which are a part of the brainstem, and the diencephalon. The rest of the tissue you see in front of you now is what is referred to as the Telencephalon, which is Latin for the cerebrum.
When you look at the cerebrum, you’ll notice straight away that it consist of two hemispheres. So the Right Hemisphere, and the Left hemisphere. And each of these two hemispheres is divided into two specific parts: the Pallium and the Sub-Pallium.
The Pallium is sort of the two outermost layers of the brain, which is the Cerebral Cortex, on the surface here filled with nerve cell bodies, and the white matter that is just underneath the cerebral cortex formed by myelinated axons. The subpallium consists of what we call the Basal Ganglia, which are nuclei located in the deep white matter of the Telencephalon. So again, the cerebral cortex is what we’re going to focus on today.
So in this video, we’re first going to look at the Functions of the Cortex. Then we’re gonna go through the different surfaces and the fissures. While doing so, we’ll go through the dural septae because they’re located within the fissures of the brain.
After that, we’re gonna go through all the Sulci and Gyri associated with each lobe. And then, in the next video, we’re going to talk about the rest of the Pallium, which is the white matter of the brain, and the Basal Ganglia So, the cerebral cortex is a highly folded sheet of neurons, which has a thickness of around 1,5-5 mm depending on the region you’re measuring. Now, why do you think the cerebral cortex differs in thickness along different regions?
Well, to understand that, we need to have a basic understanding of the cortex layers. So if we take a small sample of it and look at it underneath the microscope, you’ll see 6 distinct layers. The molecular layer is the most superficial one, then the External Granular Layer, External Pyramidal, Internal granular and Internal pyramidal, and then the Multiform layer.
The thickness of the cortex varies because these layers differ in thickness depending on the function of the specific area we’re looking at. So, for example. We got areas in the cerebral cortex we call Sensory areas that receive sensory information from the body.
The primary somatosensory cortex receives information regarding somatic sensations. These sensations detect things like touch, pain, temperature, and proprioception. We have the primary visual cortex, which receives visual sensation through the optic nerve.
We got the primary auditory cortex, which receives auditory information through the cochlear nerve. Through an MRI, in general, you’ll see that the sensory cortical areas are thinner on average, while the motor cortical areas, especially the primary motor cortex, will send down motor impulses are generally thicker, and that is because the internal pyramidal layer has a denser amount of pyramidal cells, which are the ones sending down motor pyramidal tracts like the corticospinal tract or the corticonuclear tract. Between all the primary areas of the brain, we got association areas that interpret information from the primary sensory areas.
And based on that interpretation, we react, and we communicate. So, in general, everything that goes through your cerebral cortex is conscious. Everything that does not go through your cortex is subconscious.
That is the general function of the cerebral cortex. Now. Again, We got two hemispheres.
The left hemisphere and the right hemisphere. And this is what the surfaces of these hemispheres look like, so let’s talk about that a little bit. Each cerebral hemisphere has three surfaces.
They have a medial surface facing each other, and Inferior surface that faces the cerebellum, and a superolateral surface, which is the largest surface of each hemisphere. So these are the surfaces, but we also have large fissures here in this area. We have one right here, called the Longitudinal Fissure, and these two, between the cerebrum and the cerebellum, called the Transverse Fissure.
And these fissures are occupied by a double fold of Dura Mater, called Dural Septae. I’ll show you what I mean by this if it’s unfamiliar to you and we’ll use this guy to help us illustrate this. If we take a small piece of the upper part of the skull, we’ll be able to see all the layers all the way from the skin to the brain.
So the superficial part is the skin, along with all the dermal layers. Underneath the skin layers, we have the Skull. Directly underneath that, we have the meninges, and then we have our brain tissue.
So these are the general layers, but the meninges is essentially what I want to focus on now since that is what’s primarily in the cerebral fissures we talked about earlier. So the innermost meningeal layer is the Pia Mater, which is a delicate thin layer of connective tissue. Then we have the arachnoid mater.
And in between the pia mater and the arachnoid mater is the subarachnoid space, where the cerebrospinal fluid flows. And you’ll occasionally find these arachnoid granulations here that push out the CSF from the subarachnoid space into the veins, completing the CSF circulation. And here just to quickly remind you about how the CSF circulates around our brain.
CSF is produced by the choroidal plexuses inside the ventricles in our brain, which are the lateral, third, and fourth ventricles. This fluid will circulate around in the central canal and in the ventricles and eventually go through the lateral and the median apertures from the 4th ventricle into the subarachnoid space, which will then go through these arachnoid granulations and then into the bloodstream again. So that’s the function of the arachnoid granulations, they take the cerebrospinal fluid from the subarachnoid space and then push it into the dural sinuses.
On top of the arachnoid mater lies the thickest of the meninges, called the Dura Mater. And there are two layers of the dura mater. There’s the Periosteal layer lining the internal surface of the skull and the meningeal layer that is continuous with the brain and spinal cord.
These two dural layers are bound together, and only when they separate, that’s when they form the Dural sinuses and the dural septae. So the Dural Septae restricts displacement of the brain, much like a seatbelt does for us. The Falx cerebri is the first one we’re gonna talk about.
So if we take the brain and cut it, right about… here. We’ll see this. We’ll see the Falx Cerebri located inside of the longitudinal fissure between each cerebral hemisphere.
And again, it’s formed by the double-layer…. of the meningeal part…. of the dura mater.
Falx means sickle, like this. Because the Falx Cerebri is formed like a sickle within the longitudinal fissure, as you see here. Then we have the Tentorium Cerebelli, so if we cut the brain right around here.
That’s where we’ll find the tentorium cerebelli. Tentorium means tent, so the tentorium cerebelli is like a tent above the cerebellum, Lying within the transverse fissure of the brain. So, if we take a look at this picture.
There is blue is our periosteal layer of the dura mater, and in red, there is the meningeal layer of the dura mater. And notice that the periosteal layer fuses at the foramen magnum, and the meningeal layer goes all the way down the spinal cord. That’s why there’s only one dura mater layer in the spinal cord region.
So now what we’re gonna do is that we’re gonna take this cross-section and move it back a little bit, that’s where we’re going to find the falx Cerbelli, between the two hemispheres of the cerebellum. So we got the falx cerebri, Tentorium cerebelli and falx cerebelli. These are the dural septae of our brain.
So if we go all the way back to the fissures we were talking about. The falx cerebri is here in the longitudinal fissure. The tentorium cerebelli is located here in the transverse fissure of the cerebrum.
So that was the surfaces and the fissures of the brain. Let’s now look at the lateral view to finally cover the lobes of the cerebral hemispheres. So there are 5 lobes we’re gonna talk about in this video.
And these are the Frontal Lobe, The parietal lobe, the Temporal Lobe, and the Occipital lobe. These beautiful lobes are the main large lobes on the surface of the hemispheres. But we have a deep sulcus here between the Frontal, parietal, and the temporal lobe called the Lateral Sulcus, or Sulcus of sylvius.
And if you’d open up this Sulcus, you’ll find one more lobe which is situated a little deeper, called the insula, or Insular lobe. Now. These lobes are separated by sulci The first one is the Sulcus we talked about, the lateral Sulcus.
It separates the frontal lobe from the temporal lobe and the parietal lobe from the temporal lobe. Another important sulcus we have is the Central Sulcus. Or sometimes referred to as the Sulcus of Rolando.
The central Sulcus separates the frontal lobe from the parietal lobe. Another important sulcus is the Parietooccipital Sulcus, separating the parietal lobe from the occipital lobe. So these are the main landmarks I want you to keep in mind.
Let’s now cover all the Gyri and Sulci we’ll find on the Frontal Lobe. The frontal lobe has a precentral gyrus that runs parallel and in front of the Central Sulcus. Then there’s the Superior frontal Sulcus and the inferior frontal Sulcus.
These sulci separate the brain into certain gyri. Gyri are bumps on the surface of the brain. So first of all we have the precentral Gyrus that lies between the precentral and the central Sulcus.
The precentral Gyrus is what we call the primary motor cortex. And each segment of this Gyrus is responsible for the movement of certain parts of the body. Because of this, you’ll find a map of this Gyrus we call Moto Homunculus, and it looks like this.
So one part of the precentral Gyrus is responsible for the movement of the lower extremity. Another part is responsible for the movement of the Trunk, the upper extremity, and the face, and so on. Um.
You’ve probably seen this figure somewhere in your life. This figure is a distorted representation of the human body, based on the neurological map of the areas and proportion of the human brain dedicated to processing motor functions of specific areas. So for example.
You see the hands and the face are very big compared to the trunk. That means a greater portion of the precentral Gyrus is dedicated to these areas. And again, which layer of the cerebral cortex do these tracts come from?
The tracts come from the pyramidal cells of the internal pyramidal layer. These tracts are what we call Pyramidal tracts that give off voluntary movement. These tracts are the corticospinal tract and the corticonuclear tract.
So that is the precentral Gyrus. Now. Above the superior frontal Sulcus lies the superior frontal Gyrus.
Between the superior and the inferior frontal Sulcus lies the middle frontal Gyrus. And below the inferior frontal Sulcus lies the Inferior frontal Gyrus. These gyri are referred to as the prefrontal cortex and have association areas that make up our personality.
On the inferior frontal Gyrus, you’ll find an area called Broca’s area, which is the motor speech center, which is involved in Language, speech production, and comprehension. So that was all the gyri and sulci of the frontal cortex from a lateral view. Now let’s do the parietal lobe.
The parietal lobe has a Postcentral sulcus. It’s post- because it lies after the central sulcus. Then there’s the intraparietal Sulcus separating the parietal lobe into two lobules.
Alright, let’s do the gyri. Here we’ll find the Post central Gyrus, which is the Primary Somatosensory Cortex, that again receives sensory information regarding touch, pain, temperature, and proprioception, which is basically the position of the different body parts. And again, just like the precentral Gyrus, we can draw a map of the postcentral Gyrus as well, calling it the sensory homunculus, which basically also has different regions receiving different sensations from different areas of the body.
So that is the postcentral Gyrus. The intraparietal Sulcus divides the parietal lobe into two lobules. Superior to the intraparietal Sulcus lies the Superior Parietal Lobule, which is an association area of the brain.
And below the intraparietal Sulcus lies the inferior parietal lobule, which is also a sensory association area. But here, you’ll find two gyri. You’ll find the Supramarginal Gyri, lying above the end of the lateral Sulcus, and the angular Gyrus, which is the reading center of our brain.
This area gives us the possibility to understand written words and metaphors. So that is the parietal lobe. Next, we have the Temporal Lobe.
And the temporal lobe has the superior temporal Sulcus and the inferior temporal Sulcus. And they divide the temporal lobe into three gyri. We have the Superior temporal Gyrus.
Here, you’ll find the primary auditory cortex. That receive auditory information. Where did these neurons come from?
They come from the cochlea through the cochlear nerve. This nerve will synapse with the cochlear nuclei, then cross and form the trapezoid body of pons. Then they’ll ascend as the Lateral Lemniscus and synapse with the Inferior colliculus, and through the brachium of the inferior colliculus, they’ll go to the medial geniculate body of the diencephalon and then finally go to the nuclei of the primary auditory cortex, which is here at the superior temporal Gyrus.
And when they get here, you’re consciously aware of what you’re hearing. Another area you’ll find on the superior temporal Gyrus is Wernicke’s area, which is the Sensory area of speech. In unfortunate situations where people receive a direct hit on the temporal side of the head, this area might get damaged.
And then the patient shows a condition called receptive aphasia, where their speech appears normal grammatically, but there’s no meaning in what they’re saying. There’s no sense in the words they’re saying. So this area is crucial for speech.
So that is the superior temporal Gyrus. Then we have the middle temporal Gyrus and the inferior temporal Gyrus, which are association areas as well. So that is the temporal lobe.
Next, let’s do the occipital lobe. There’s not much to say about this lobe from this perspective, as you’re only really seeing a small portion of it. But if we turn this image to the other side, we can look at the medial surface of the cerebral hemisphere.
Let’s now focus on the gyri and sulci we see here in this area, so let’s remove the brainstem so that we see as much of the cortex as possible. So first off, we have a deep fissure here we call Cingular sulcus. This Sulcus continues backward and eventually becomes the subparietal Sulcus.
And what this Sulcus does is that it separate the frontal lobe and the parietal lobe from the cingulate Gyrus. The gyrus cinguli is a part of the limbic system, which is a system responsible for processing emotions and behavior regulation. Then we have a paracentral sulcus and a marginal sulcus.
And in between them, there’s an area we call the paracentral Gyrus, which is a part of the precentral and the postcentral Gyrus. The majority of the frontal lobe, the blue area you see here, is a part of the superior frontal Gyrus, which we looked at earlier. Then if we shift our focus to the posterior side, we’ll find the parietooccipital Sulcus.
Which remember is the landmark between the parietal lobe and the occipital lobe. In front of the parietooccipital Sulcus, there’s the precuneus, which is an association are located in the parietal lobe. But behind the parietooccipital Sulcus, you’ll find Cuneus, which is a part of the occipital lobe.
The Cuneus contains the primary and secondary visual cortex. So let’s go through the visual pathway again. On the retina of the eyeball, we have receptors for the optic nerve, the 2nd cranial nerve, that leave the eyeballs.
Half of these tracts will cross to the other side and form the optic chiasm. Then they’ll synapse with the lateral geniculate bodies and then go to the primary visual cortex, which is the Cuneus of the occipital lobe. When the nerve goes to the primary visual cortex, that’s when we’re consciously aware of what the eyes perceive.
These fibers can also go to the superior colliculus to activate reflex movement associated with vision. So that’s the Cuneus. Then we have a sulcus called Sulcus Calcarinus that separates the primary and secondary visual cortex.
We have a collateral sulcus, and we have an occipitotemporal sulcus that borders the occipital lobe from the temporal lobe. The collateral sulcus separates the lateral occipitotemporal Gyrus, from the medial occipitotemporal Gyrus and the Parahippocampal gyrus. The lateral occipitotemporal Gyrus is sometimes referred to as the Fusiform gyrus.
The medial occipitotemporal Gyrus is sometimes referred to as the Lingual Gyrus. And these two areas are what we call visual association areas. So they take in information from the primary visual cortex, and they give you the possibility to take past experiences, let’s say someone's face, or maybe even a flower or a facial expression.
And it helps with recognition. It gives meaning to the image you’re seeing. So the Cuneus, the Lateral Occipitotemporal Gyrus, and the medial occipitotemporal Gyrus are all a part of the occipital lobe.
Awesome. The parahippocampal Gyrus is kind of a continuation of the cingulate Gyrus. SO it’s also a part of the limbic system.
Lastly, the Gyrus down here is the inferior temporal Gyrus we talked about earlier. So that’s these. What other structures do we see here?
We have the Sulcus of the corpus callosum, which divides the Cingulate Gyrus from the Corpus Callosum. The corpus callosum itself doesn’t really have an actual function. However, it’s a really important part of the brain because it contains a lot of fibers that connect both hemispheres.
That’s really what it does. It just has fibers that go from the left hemisphere to the right hemisphere and vise versa. Now, another sulcus we can find is the Hippocampal Sulcus.
And that is a sulcus that divides the Parahippocampal gyrus from the Dentate Gyrus. The dentate Gyrus is a part of the hippocampus, which I’ll talk about in the next video. And it contributes to forming new memory.
Now. From the parahippocampal Gyrus, it’s going to continue, as Uncus. And the uncus is a hook-like structure that is a part of the olfactory cortex, receiving information about the smell.
The last thing I wanna mention here on the medial surface is a narrowing that is associated with the cingulate Gyrus. And that is the isthmus of the Cingulate Gyrus, which is located here in this area. So that was all the structures for the medial surface.
Now, if we look at an inferior view of the brain, we’ll find the olfactory nerve, which is the cranial nerve number 1, and the Optic chiasm of the optic tract. The olfactory nerve lies on a sulcus called the olfactory Sulcus. And the olfactory Sulcus divides the lower surface of the frontal lobe into two parts.
It divides it into the Gyrus rectus, which is a part of the prefrontal cortex. And the Orbital frontal gyri, or gyri orbitales. Which is also a part of the prefrontal cortex.
On this gyri, you’ll find many small sulci called orbital sulci, or orbital frontal sulci. So that was all of these lobes. Lastly, let’s open up the lateral Sulcus and talk about the insular lobe.
Now. What I want you guys to know about the insula are two things. One is that it’s divided into the short gyri of Insulae and the long Gyrus of insulae.
And two is that the insula is responsible for receiving taste sensations. So gustation. The insula is what we call the gustation cortex because it perceives taste.
It tells us what kind of taste it is, if it’s sweet, if it’s sour, if it’s bitter, if it’s salty or if it’s umami. You know. The other function of the Insula is Visceral sensation.
So sensations come from the GI tract, the heart, the lungs. If a person has gastroenteritis. The pain from that GI tract will go to the insula and make you aware of that.
The last function is that it’s believed that this may be where your vestibular cortex is located. And the vestibular cortex would be involved with your vestibular sensation. Which is basically your sense of movement, right?
So static equilibrium and rotational acceleration and all of those things may go to the insula. Alright, guys, so that was a video about the cerebral cortex, If you found this video helpful, please put a like, comment, share, whatever you find convenient to you. The next video will be about the internal structures of the Telencephalon.