Anatomy of the cerebral cortex

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Introduction0:00–0:52

Now, we know what you're thinking. Don't worry, you're at osmosis, we're not telepathic.
But by watching this video on the cerebral cortex, we know you have the brain on your mind. So let's get to it.
The human central nervous system basically consists of the spinal cord and the brain which includes the cerebrum, diencephalon, cerebellum and brainstem.
Taking a closer look at the cerebrum. It consists of two nearly symmetrical halves called the cerebral hemispheres and the basal ganglia also referred to as basal nuclei.
Furthermore, each cerebral hemisphere is divided into four main lobes, the frontal parietal, temporal and occipital as well as what's become to be known as the fifth lobe, the insula or insular cortex.
If we were to cut through the cerebral hemispheres in the coronal plane, which means transecting from left to right and dividing the brain into rostral and caudal divisions.

Cerebral Hemispheres0:52–2:06

We would see the cerebral cortex. This is the outermost area of the cerebral hemispheres and it's composed of gray matter containing billions of nuclei or neuronal cell bodies.
A cell body and its dendrites along with its axon and synaptic terminal, collectively make up a structure called a neuron neurons thus allow for information processing and communication with other neurons within the nervous system.
The gray matter gets its name from its dark appearance during gross inspection, deep to the gray matter is a subcortical white matter which is made up of myelinated axons connected to the nuclei of the gray matter.
White matter gets its name because the myelination of axons gives this area a white appearance on gross inspection. The largest white matter tract is a corpus callosum which sends signals between the two cerebral hemispheres, essentially connecting them together.
Found throughout the subcortical white matter are further collections of gray matter masses containing neuronal cell bodies referred to as the basal ganglia also called the basal nuclei.

Basal Ganglia2:06–2:55

The basal ganglia consist of the caudate and putamen. The globus pallidus, the subthalamic nucleus and the substantia Nigra note that the term striatum refers to the caudate and putamen.
The term lentiform nuclei or lenticular nuclei refers to the putamen and globus pallidus. And the term corpus striatum refers to all three structures.
The caudate, the putamen and the globus pallidus. All the structures of the basal ganglia have their own unique functions and pathways running in between these basal ganglia are more white matter afferent and efferent axon tracts.

Internal Capsule2:55–3:34

The most notable being the internal capsule. The internal capsule is a collection of densely packed white matter or axons which divides the corpus striatum and acts like a highway for information flow between the cerebral cortex and the brainstem and spinal cord, generally, the right cerebral hemisphere sends and receives signals from the left side of the body.
While the left hemisphere sends and receives signals from the right side of the body. Now taking a step back and looking at the external surface of the brain, we can see that the cerebral cortex is not flat but covered with many folds called gyri, which are separated by shallow grooves called sulci or by deeper grooves or clefts called fissures.

External Surface of the Cerebral Cortex3:34–4:23

One function of these gyri and sulci is to allow nearly 2.5 square feet of the cerebral cortex to fold in on itself, allowing it to fit within the small space of the narrow cranium just like the folds of an accordion when it's closed.
A second advantage of this cortical folding is that it effectively increases the surface area allowing more nuclei to be packed into the cortex.
This greater number of nuclei allows for more signaling and therefore more advanced processing and higher cortical function.

Brodmann areas4:23–5:16

The deep fissures also help to separate the brain into lobes. Even though the brain looks like it has a random configuration of ridges and clefts.
The gyri sulci and fissures actually create a relatively constant pattern from person to person. This pattern can be used to identify certain external landmarks of the brain which have very specific functions.
We not only can define the cerebral cortex by lobes or functionality which we'll talk about soon, but the cerebral cortex can also be divided into histologically similar regions called brodmanns areas.
This means that the neurons within a particular broadens area are all arranged in the same manner and partake in a similar function.
Approximately 100 and 80 Brodmann's area have been identified in the human brain through MRI and other mechanisms. We'll mention Brodmann's area for some of the primary areas of cortex shortly.
So let's take a closer look at the different sulci and deep fissures that separate the brain into five lobes. The frontal lobe, parietal lobe, temporal lobe, occipital lobe and insula.

Sulci and deep fissures5:16–6:54

When seen from above the cerebrum has a deep midline sagittal fissure called the longitudinal fissure which divides the brain into left and right cerebral hemispheres deep within this fissure is the already mentioned corpus callosum.
Still looking from above around the midline of the longitudinal fissure and moving laterally is the coronal central sulcus also known as a fissure of Rolando which separates the frontal lobe rostrally or anteriorly from the parietal lobe caudally or posteriorly.
The rostralmost point of the frontal lobe is called the frontal pole. The central sulcus can also be seen on a lateral view of the brain traveling inferiorly across the lateral aspect of the hemispheres.
From this lateral view beneath the frontal and parietal lobes is a lateral fissure also known as a lateral sulcus or Sylvian fissure.
The lateral fissure is found mainly on the lateral and inferior surface of the cerebral hemispheres and it separates the frontal and parietal lobes above from the temporal lobe below the lateral fissure extends in three directions rostrally as the anterior ramus superiorly as the ascending ramus and caudally as a posterior ramus.
The most rostral point of the temporal lobe is called the temporal pole. Furthermore, the area of the cortex called the insula or insular cortex lies at the bottom of the lateral fissure hidden from the external surface of the brain.

Insula6:54–7:20

So we need to open up the folds of the lateral fissure or dissect them. In order to see it, the insula has the central sulcus of the insula running through it forming both short gyri rostral to the sulcus and long gyri caudal to the sulcus.
Looking at the brain from a posterior view around the posterior middle portion of the cerebral hemisphere. There's a fissure called the parietal occipital fissure which travels inferiorly and anteriorly.

Parieto-occipital fissure7:20–7:55

The parietal occipital fissure separates the parietal lobe rostrally from the occipital lobe caudally and from a medial view of the hemisphere, the parietal occipital sulcus is joined halfway by the calcarine sulcus.
The most caudal point of the occipital lobe is called the occipital pole. Now that we've outlined the general boundaries of each lobe, let's look at the components of each lobe in more detail, starting with the frontal lobe on the lateral aspect, rostral to the central sulcus is the precentral sulcus that runs parallel to it together, the central sulcus and the precentral sulcus form the borders of the precentral gyrus.

Frontal lobe boundaries7:55–8:44

From the rostral side of the precentral sulcus arise two more horizontal sulci, the superior frontal sulcus and the inferior frontal sulcus which extend toward the frontal pole.
These divide the rest of the frontal lobe into three gyri and going from medial to lateral. These are the superior, middle and inferior frontal gyri.
The inferior frontal gyrus is divided into three parts by the branching rami of the lateral fissure. First, inferior to the anterior ramus is the orbital part or pars orbitalis.

Inferior Frontal Gyrus8:44–9:41

Then between the anterior ramus and the ascending ramus is a triangular part or pars triangularis. And finally posteriorly between the ascending ramus and the precentral sulcus is the opercular part or pars opercularis.
If we cut a sagittal section, meaning cutting the brain in half along the longitudinal fissure and look at the frontal lobe from a medial view.
We can also see another sulcus called the cingulate sulcus as well as the anterior paracentral lobule, which forms the medial aspect of the precentral gyrus and the posterior paracentral lobule, which forms the medial aspect of the postcentral gyrus, which we'll mention later by understanding the different anatomical landmarks of the lobes.

Primary motor cortex9:41–10:27

We can start to identify the different functionally specialized regions of the cerebral cortex. For example, the regions of our cortex that are responsible for controlling motor or sensory functions that assist with our everyday lives.
When considering the functional areas of the frontal lobe, it contains a primary motor cortex or broad's area four that occupies the area of the precentral gyrus and extends over to the medial aspect of the hemisphere.
As the anterior paracentral lobule. The primary motor cortex houses neurons responsible for carrying out voluntary movements of different parts of our body, mainly to the contralateral or opposite side, extending anteriorly from the primary motor cortex and over the posterior parts of the superior medial and inferior frontal gyri is a premotor cortex or Brodmann's area six.

Premotor cortex10:27–11:15

This premotor cortex receives input from other parts of the cerebral cortex. The thalamus, the basal ganglia and directly communicates with the primary motor cortex.
Its function is to assist the primary motor cortex plan and carry out voluntary movements and therefore, it's called an association cortex.
The premotor cortex essentially stores and processes information about past activity and helps to integrate sensory and motor information for planning of future voluntary movements, rostral to the premotor cortex and extending into the middle frontal gyrus is a frontal eye field or broad one's area eight which controls voluntary eye movement and allows us to move our eyes together in the same direction at the same time, known as conjugate gaze.

Frontal eye field11:15–11:36

The next area we're going to look at is Broca's area. Brodmann's area 44 and 45 which is formed by two regions of the inferior frontal gyrus, namely the pars are perulus and the pars triangularis.

Broca area11:36–12:14

Broca's area is usually located in the dominant hemisphere, which in most individuals is the left hemisphere. This area has connections to the nearby motor cortex, specifically to the areas that control the muscles of the larynx, mouth, soft palate, and the tongue, as well as respiratory muscles to assist in the formation or production of words and speech.

Prefrontal cortex12:14–12:42

And lastly, we have the prefrontal cortex which is located anterior to the premotor cortex and overlies the anterior portions of the superior, middle and inferior frontal gyri.
The prefrontal cortex has rich connections to other parts of the brain. And it's responsible for mainly what has been coined as executive functions, which would include reasoning, planning, social behavior, judgment and much more.

Functions of Primary motor cortex12:42–13:08

Let's take our attention back specifically to the primary motor cortex, which again is responsible for controlling voluntary movements of our body.
The nuclei of neurons that will control a certain region of the body are organized together so that all the nuclei that will control the muscles of the face are organized in one specific region of cortex.
While all the nuclei associated with controlling the foot are organized in another this unique and elegant arrangement of body parts in the cortex is called somatotopy.

Somatotopy13:08–14:58

This can be visually represented by drawing the body part above the cortical area that controls it. So it looks like this where each body part is noted on top of its corresponding cortical area.
Now, the proportion of the primary motor cortex or the number of neurons dedicated to a particular movement, depends on how much that muscle or group of muscles is actually used.
So the more a muscle is used, the more nuclei will be dedicated to it within the cortex. The number of nuclei is independent upon the size or mass of the muscle, performing that movement.
But it is based on how important that muscle is to your everyday life and functioning. So when we quantify the proportions of neurons in the primary motor cortex utilized by the muscles in each individual body part, we get a strange looking humanoid figure that's called the motor homunculus, which in Latin means little human.
As you can see, this primary motor cortex map creates an awkwardly large representation of the hands, fingers and face. This means that more cortex and hence more neurons are dedicated to those regions.
Since we use them more often in our daily lives to explore our world. Going back to our primary motor cortex map, we can see that the location of the body parts is essentially inverted anatomically on the primary motor cortex.
Starting at the superior medial part of the primary motor cortex. In the anterior paracentral lobule, the toes are represented first and then as one moves laterally through the primary motor cortex, the more superior parts of the body are progressively represented with the more lateral and inferior part of the primary motor cortex representing the most superior parts of the body such as the head and neck.

Parietal Lobe14:58–15:32

Ok. Let's move on to the parietal lobe.
On the lateral view, just caudal to the central sulcus running parallel to it is the postcentral sulcus together the central sulcus and the postcentral sulcus form the borders of the postcentral gyrus running caudally from the middle of the postcentral sulcus or near it is the intraparietal sulcus which divides the rest of the parietal lobe into the superior parietal lobule above it and the inferior parietal lobule below it.
Remember the posterior ramus of the lateral fissure. Well, there's a part of the inferior parietal lobule that folds over the end of the posterior ramus.

Supramarginal Gyrus15:32–15:52

And it's called the supramarginal gyrus. And behind it is the angular gyrus that folds over the end of the superior temporal sulcus found in the temporal lobe.
This takes us to the functional regions of the parietal lobe similar to the primary motor cortex. There's also a primary somatosensory cortex or Brodmann's area 31 and two, which is located in the postcentral gyrus and extends medially to the posterior paracentral lobule.

Functional regions of the parietal lobe15:52–16:30

The primary somatosensory cortex receives sensory input from the opposite side of the body to the ventral posteromedial or VP M and ventral posterolateral or VPL nuclei of the thalamus enabling us to process and interpret sensory information from our body like touch or pain.
And similar to the motor homunculus. We have a sensory homunculus to visually represent the proportion of sensory fibers that the primary somatosensory cortex receives from a particular part of the body.

Sensory Homunculus16:30–17:24

The more sensitive a body part is the more neurons it requires for processing sensory stimuli. And therefore, it occupies a larger area of the somatosensory cortex.
And again, similar to the primary motor cortex, starting from the deeper, more medial aspect of the primary somatosensory cortex in the posterior paracentral lobule.
The first body part represented here is the anal genital area followed by the foot, leg and thigh. As we cross over to the lateral side and move inferiorly along the postcentral gyrus.
The thigh is followed by the trunk, upper limb and the head and neck and then the intraabdominal organs then located over the superior parietal lobule is the somatosensory association cortex which has many connections with other sensory regions of the cerebral cortex.

Somatosensory association cortex17:24–17:53

The somatosensory association cortex is believed to allow the ability to integrate different sensory modalities such as being able to recognize objects through touch without visual input, like reading braille.
By comparing and associating the sensations to past sensory experiences. That was a lot of brain to take in for the brain.

Quiz17:53–18:14

Let's take a moment to pause and see if you can identify some of the different regions of the brain. Now, can you label these functional areas of the brain?

Temporal Lobe18:14–18:47

Now, let's continue our journey and examine the temporal lobe which lies inferior to the lateral fissure and extends posteriorly to the occipital lobe.
The lateral surface of the temporal lobe includes the superior temporal sulcus and the middle temporal sulcus which divide the temporal lobe into the superior middle and inferior temporal gyri deep inside the lateral fissure.
There's also the transverse temporal gyri of Heschel which is found on the deep upper surface of the superior temporal gyrus.
Now let's look at the functional regions of the temporal lobe located in the transverse temporal gyri of Heschel is the primary auditory cortex.

Primary Auditory Cortex18:47–19:13

Brodmann's area 41 and 42 which receives auditory input from the medial geniculate body of the thalamus and interprets auditory information or sound such as when the next door neighbors are being way too loud, go then on the dominant hemisphere which again is most often the left we have Wernicke's area or Brodmann's area 2239 and 40 which encompasses a part of the superior temporal gyrus along with the supramarginal and angular gyri of the parietal lobe.

Wernicke area19:13–19:56

Fn's area is responsible for the processing and understanding of both written and spoken language, allowing us to read a sentence, understand it and say it out loud comprehensively.
It's also connected to Broca's area by a bundle of axons called the arcuate fasciculus, which allows us to tie together speech comprehension from Wernicke's area and speech production from Broca's area.
A second important function of the temporal lobe. And specifically the medial aspect of the temporal lobe is that it houses limbic system structures related to learning memory and emotion, which we'll get to later, we also spoke previously about the insula known as the fifth lobe of the brain, which is found deep in the lateral fissure.

Limbic system19:56–20:09

Insula20:09–20:40

The insula is usually divided into anterior and posterior aspects. Functions are diverse and complex with convergence of inputs from temporal parietal and frontal lobes.
The insula has been associated with processing visceroautonomic sensations, limbic and emotional elements, somatosensation and possibly motor elements too.

Occipital Lobe20:40–21:08

Moving on. Let's get to the final lobe on our journey.
The occipital lobe which lies caudal to the rito occipital sulcus. The occipital lobe contains a cuneus, a wedge shaped area bounded by the parietal occipital fissure rostrally and by the calcarine sulcus inferiorly inferior to the cuneus.
And the calcan sulcus is a lingual gyrus. When considering the functionality of the occipital lobe, this area of cortex is dedicated to vision and hence, a substantial part is occupied by the primary visual cortex.

Primary visual cortex21:08–21:44

Brodmanns area. 17, the primary visual cortex is loaded on the medial aspect of the hemispheres and lines, both the superior and inferior banks of the Calcan sulcus.
It also extends around the occipital pole onto the lateral surface of each hemisphere. This area it receives processes and interprets visual input from the lateral geniculate body of the thalamus.
Finally, on the medial side of each hemisphere, there's a region of cortex surrounding the corpus callosum, that's part of the limbic system.

Corpus callosum21:44–22:09

This region contains the subcallosal gyrus located below the rostral part of the corpus callosum as well as the cingulate gyrus, which begins beneath the rostral end of the corpus callosum and continues superiorly and caudally until it reaches the posterior end of the corpus callosum.

Parahippocampal gyrus22:09–22:49

The parahippocampal gyrus which is part of the medial temporal lobe lies rostral to the lingual gyrus of the occipital lobe and ends rostrally at the uncus.
Also a component of the limbic system. These cortical structures along with the olfactory cortex, the amygdala, the hypothalamus and the hippocampus constitute the major structures of the limbic system.
They are responsible for functions related to the preservation of the species such as fight or flight responses, emotion, memory and reproductive endocrine and other behavioral responses.
All right. As a quick recap, the cerebrum consists of two cerebral hemispheres or the cerebral cortex is the outermost layer and consists of gray matter which contains neuronal cell bodies or nuclei located beneath the gray matter is a subcortical white matter which is composed of myelinated axons found within the subcortical white matter are further gray matter masses such as the basal ganglia or basal nuclei.

Review22:49–26:27

The external surface of the cerebral cortex is formed by gyri sulci and fissures. The longitudinal fissure separates the two cerebral hemispheres which are connected via the corpus callosum.
The central sulcus, parietal occipital fissure and the lateral fissure divide each cerebral hemisphere into four main lobes, frontal parietal occipital and temporal lobes.
The cerebral cortex can also be divided into histologically similar regions called Brodmann's areas which provides a map of the primary cortices and functional regions.
The main anatomical regions of the frontal lobe are the precentral sulcus, precentral gyrus and the superior and inferior frontal sulci which delineate the superior, middle and inferior frontal gyri.
The frontal lobe has five functional regions, primary motor cortex, premotor cortex, the frontal eye field, broca's area and the prefrontal cortex.
The motor homunculus is a visual representation of the areas of primary motor cortex dedicated to the voluntary motor control of body parts.
The parietal lobe contains the postcentral sulcus and intraparietal sulcus that border the postcentral gyrus, superior parietal lobule and inferior parietal lobule.
Its functional regions are the primary somatosensory cortex. The somatosensory association cortex and the supramarginal and angular gyri that both contribute to Wernicke's area.
The sensory homunculus is a visual representation of the proportion of sensory axons. The primary somatosensory cortex allocates to a particular part of the body.
The temporal lobe contains a transverse temporal gyrus of Heschel, which includes the primary auditory cortex and the superior temporal gyrus that contributes to a part of Wernicke's area structures in the medial temporal lobe are important to learning memory and emotion.
The occipital lobe contains a cuneus and lingual gyrus separated by the calcarea sulcus and these areas comprise the primary visual cortex deep within the lateral fissure is the insula or fifth lobe and finally around the corpus callosum, we have a strip of cortex, the subcallosal gyrus and the cingulate Gyrus that are both part of the limbic system.