Cerebral Cortex (Function, Covering, Lobes, Sulcus, Gyrus, Fissures) | Anatomy

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.