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