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Structures seen on the medial view of the brain. The images show a midsagittal section of the brain.
Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the medial view of the brain. So, essentially, what we’re going to be doing on this tutorial is looking at the structure seen on this image from the medial aspect of the brain in the sagittal plane. We will be highlighting the various structures that can be seen from this aspect and give you a brief overview about the function of these structures we can see. So, the purpose of this tutorial is to point out the structures that can be identified when we take then the mid-sagittal section of the brain.
The order in which I will be presenting these structures today is to start first with describing the structures of the hemispheres then followed by the structures of the diencephalon and, finally, the structures of the brainstem. Since we are going to look at the structures of the cerebral hemisphere first, I would like to begin with the anterior most part of the cerebral hemispheres which is then the frontal lobe. But this structure that you see now highlighted in green is known – to be more specific – as the medial frontal gyrus.
So, as I mentioned, this structure is part of the frontal lobe of the brain and it is then the continuation of the superior frontal gyrus seen on the medial surface of the frontal lobe superior and rostral to the cingulate sulcus. It is part of the so-called prefrontal cortex and is one of the most critical parts of the brain because it is responsible not only for focusing on task but also working out what other areas need to do and in order to solve a problem.
The next structure I’m going to be highlighting here, this one is found just behind the medial frontal gyrus, we seen then this one which is the paracentral lobule. Now, the paracentral lobule is the convolution at the medial hemispheric surface which then connects the medial portions of the precentral and postcentral gyri. Now, this lobule as you can see here on this illustration surrounds the medial end of the central sulcus. This sulcus separates the frontal lobe from the parietal lobe but you can see it a little bit better if you look at our tutorial where we explore the lateral surface of the brain.
Now, from a functional point of view, the paracentral lobule will be controlling both motor and sensory innervation of the contralateral lower extremity as well as the regulation of some autonomic functions such as defecation and urination. Now, this structure is then supplied by the anterior cerebral artery.
I would like to also show you here the boundaries of the structure that we just talked about before, the boundaries of the paracentral lobule. And, as you can see here on this illustration, the superior boundary corresponds to the superior margin of the hemisphere. So, the anterior border is the paracentral sulcus seen here highlighted in green. The posterior border is formed by the marginal sulcus which is the final part of the cingulate sulcus and separates the paracentral lobule from the precuneus. Finally, the crucial landmark that bounds the paracentral sulcus inferiorly is then known as the cingulate sulcus.
The next structure we’re going to be highlighting here now seen on the screen is known as the precuneus. It’s right posterior to the paracentral lobule we see the structure. This structure is part of the parietal lobe and is located between the marginal sulcus and the parietooccipital sulcus which you see here highlighted in green respectively. And I want to mention here – I have to mention here actually – that as the name suggests, this sulcus – the parietooccipital sulcus is the border between the parietal and occipital lobes. So, this one that you see here on the image.
Next, we’re going to be highlighting this structure which is known as the cuneus, which is found posteriorly to the precuneus, and this is a part of the occipital lobe that is located between the parietooccipital sulcus and the calcarine sulcus, which you see here respectively. So, here on the top portion, you see the parietooccipital sulcus and here on the lower image you then see the calcarine sulcus, which happens to be then the focus of the next topic.
So, as I said previously, the calcarine fissure is located in the occipital lobe below the cuneus and meets then the parietooccipital sulcus at an acute angle anteriorly. So, as you can see here, it forms an angle between then the parietooccipital sulcus which is this one that you see here. You have to remember that the calcarine fissure that you now see here from an anterior view of the cerebral cortex corresponds to the Brodmann area 17 and it is the primary visual cortex.
The next structure we’re going to be highlighting now is known as then the cingulate gyrus. So, this is another important part of the cerebral cortex. It is seen on the medial aspect of the cerebral hemispheres is then this one, the cingulate gyrus. Now, this gyrus is located between the cingulate sulcus and the sulcus of the corpus callosum. Today, the cingulate gyrus is then considered as part of the limbic system and it is implicated in many higher cognitive functions including memory and emotional response. Now, just below the cingulate gyrus we see then the sulcus of the corpus callosum which takes its name from the largest commissure of the brain that lies below it then the corpus callosum.
So next, we’re going to be talking about the corpus callosum so you see here highlighted in green which is located at the base of the longitudinal fissure of the cerebrum which you see also here on this image, the corpus callosum, where we just made a cut here on the brain – a transverse and a coronal cut – and you can see here then exposed and highlighted the corpus callosum. This is the largest commissure of the brain comprising of mass of transverse fibers connecting then the left and right cerebral hemispheres, and you can even see here perfectly on this image how the corpus callosum is then connecting the right and left cerebral hemispheres.
Now, the corpus callosum which you also see here on this image has four parts: the rostrum which is the portion that is continuous with the lamina terminalis, there is then the genu which is the curved anterior most part of the corpus callosum that bends inferiorly in front of the septum pellucidum, there is also the body which you see here a cut but this is the body of the corpus callosum which is located between the genu and the splenium which is the next structure, the splenium, and the splenium is then the posterior part of the corpus callosum.
Now, as I mentioned previously, the corpus callosum is the largest commissure of the brain but there are four more commissures that are visible in this medial view of the brain. Here, you can see one of these four commissures which is then the anterior commissure. You can also see it here on this other image where you see then the highlight of the anterior commissure. Now, this one connects the left and right cerebral hemispheres and contains fibers from the temporal cortex, the olfactory areas, and the amygdala.
Now, another band of nerve fibers that crosses the midline is known as the posterior commissure and is located between the pineal recess and the entrance to the cerebral aqueduct. Now, the posterior commissure plays a role in pupillary light reflex.
Another commissure that we have seen on this plane is the habenular commissure which connects the habenular nuclei on both sides of the diencephalon. Now, these nuclei receive fibers from the amygdala and the hippocampus but their exact function is unknown to us.
The final commissure that we can see from this medial aspect of the brain is known as the fornix. Now, this structure is made up of curved bundle of nerve fibers that pass in both directions and connect the hippocampus with the mammillary bodies being then the main efferent system of the hippocampus. Now, the fornix can be divided – and you can also see a bit better here on this image – now, the fornix can be divided into the two crura which are the two posterior columns of the fornix which are formed as the fimbria of the hippocampus increase in thickness, as you can see here.
There is also the body of the fornix as the bundles of fibers of the crura come together – as you can see here – in the midline and they form then the body of the fornix. Now, the body of the fornix extends anteriorly and then divides at the level of the anterior commissure into the right and left halves call then the columns of the fornix. Finally, the left and right crura of the fornix communicate with each other across the midline by partially decussating fibers called the commissure of the fornix or hippocampal commissure or psalterium. So, until now, we have seen the structures of the cerebral hemispheres that are seen in the medial view of the brain as well as the major commissures of the brain that are visible in this plane.
The next structure we’re going to look at is located between the corpus callosum and the fornix and that is then the septum pellucidum. It is a thin bilayer triangular plate that separates the anterior horns of the left and right lateral ventricles of the brain from one another. The two layers of the septum pellucidum as you can see here now on this image – made a few cuts – but you can clearly see the two layers of the structure. They are comprised of gray and white matter. Now the septum pellucidum is attached superiorly and anteriorly to the corpus callosum while posteriorly and inferiorly, it is then attached to the anterior part of the fornix. So, to be a bit clear here, we’re looking at the anterior portion of this structure and here should be then the posterior portion.
Next, we’re going to be looking at this image here which shows the lamina terminalis. We have already mentioned the lamina terminalis earlier in this tutorial in reference to the location of the corpus callosum. So, now let’s take a look at this structure independently. Now, the lamina terminalis is basically a thin wall forming the anterior border of the third ventricle of the brain as we saw earlier and it is also connected in its superior and with the rostrum of the corpus callosum.
Another structure at the lowest part of the lamina terminalis that can also be seen on the medial aspect of the brain is the optic chiasm. The optic chiasm is a flattened, quadrangular-shaped body in the front of the pituitary gland where some of the axons of the optic nerve cross to the opposite side – you can also see here the pituitary gland. Specifically, the axons from the nasal retina cross to the opposite side whereas axons from the temporal retina run directly caudal without crossing. Now, here as you can see on this illustration of the base of the brain, you clearly see now the optic chiasm. This is where the nasal part of the optic axons decussate.
The next image that we’re going to be seeing here highlighted in green is known as the supraoptic recess which is also known as the optic recess and this is a recess of the third ventricle. This small, angular recess as you can see also here on this illustration is located above the optic chiasm. Now, on this image, you see a bit more here of the, another recess of the third ventricle is known as the infundibular recess. As the name suggests, it is located in the infundibulum of the third ventricle. And, as you can see a bit more clearly here in this illustration the infundibular recess is located caudal to the supraoptic recess, forms then the median eminence in which the stalk of pituitary gland is then attached –so, this is what we’re talking about, the stalk of the pituitary gland which is the structure.
Medially, caudal to the infundibular recess, we see a paired round elevation known as the mammillary body or the mammillary bodies. So, these are round elevations – as I mentioned – on the floor of the diencephalon that are part of the limbic system. The mammillary bodies as you can see also from this image and also this image of the base of the brain, you can see clearly here the two mammillary bodies. Now, as you can see, they consist of two groups of nuclei namely the medial mammillary nuclei and the lateral mammillary nuclei. These two paired structures which are connected to the hippocampus via the fornix and also with the thalamus via another bundle of fibers known as the mammillothalamic tract, relay impulses through the mammillothalamic tract from the amygdala and the hippocampus to then the thalamus.
From a functional point of view, the mammillary bodies with their connection to the limbic system are also related to memory formation. A very important point that you have to remember is that the optic chiasm, the infundibular recess and the mammillary bodies, they form the inferior wall of the hypothalamus.
Next structure we’re going to be seeing here highlighted in green is known as the pituitary gland. Now, this is another small but very important structure that can be seen here from the medial view of the brain and is also known as the hypophysis. As I mentioned earlier, the infundibular recess forms the median eminence from which the pituitary gland hangs. It is an endocrine gland that protrudes off the top of the hypothalamus at the base of the brain – and you can see it also here on this image of the base of the brain or the inferior view of the brain. Now, it also sits in the hypophyseal fossa of the sella turcica when you look at the base of the skull. Now, this small, pea-shaped body is then comprised of the anterior lobe (adenohypophysis) and also the posterior lobe or the neurohypophysis.
Now, as for the function associated to the pituitary gland, now being an endocrine gland, is then the synthesis, storage and secretion of hormones under the control of the hypothalamus. We will not go into detail about the hormones created by different parts of the pituitary gland as this will be then covered in more detail in a separate tutorial. However, please note that the hormone secreted by this gland help control several body processes including growth, blood pressure, pregnancy, childbirth, lactation, temperature regulation, sex organ function, metabolism, pain relief, water balance, etc. so, this small gland is really quite important for your body.
We’re also going to talk about another gland here that you see from this view, this one is known as the pineal gland. This is also an endocrine gland, sometimes, was referred to as the pineal body or epiphysis. The pineal gland is then suspended from the habenula and lies in a groove between the thalamic bodies. Now, this small but important structure releases a hormone known as melatonin which is a derivative of serotonin, and plays a major role in regulation of circadian rhythm.
Another structure of the diencephalon which can be seen in this medial view of the brain and specifically in the region of the third ventricle is known as the interthalamic adhesion. The interthalamic adhesion is then comprised of nerve cells or nerve fibers and, as the name suggests, connects the left and right thalami at their medial surface and you can also see here the adhesion on this view.
Now, let’s move on to look at the structure here which is one of the structures in the brain where the cerebrospinal fluid or CSF is produced then that is the choroid plexus of the third ventricle. There are four choroid plexuses one in each ventricle of the brain. The choroid plexus of the third ventricle hangs from the roof the third ventricle. It is continuous anteriorly with the lateral ventricles via the interventricular foramen. Other than production of CSF, the choroid plexus also acts as a filtration system and epithelial cells from the choroid plexus form the blood-CSF barrier which has a similar function to the blood-brain barrier.
Now, that we covered the structures of the mesencephalon, it’s time to move on and look at the different structures of the brain stem that are visible in this view. But before we start, let me make it clear that the brainstem is composed of three parts: the midbrain or mesencephalon – you see here now the brainstem from a medial view as well but we just added here the cranial nerve nuclei - a bit further down, you find then the pons and the medulla oblongata.
Now, let’s look at the superior most part of the midbrain and that is the superior colliculus which is a paired structure of the midbrain. The two superior colliculi are located between the thalamus and you can see here the thalamus on these two images and highlighted in green, the superior colliculus. They also surround the pineal body and the two superior colliculi are connected with the optic pathway especially with the lateral geniculate nucleus of the thalamus and are involved in preliminary visual processing in directing eye movement.
From this view of the brain, we also see here the inferior colliculus which is also, as the superior one, a paired structure. The two inferior colliculi which are also elevations of the quadrigeminal plate, but are instead connected to the auditory pathway, are located below then the superior colliculi. We can also move here to these images to show you the inferior colliculi from this posterior view of the brainstem where, if you remember, these are the superior colliculi. The inferior colliculi receive input from various nuclei in the brainstem and projects this information to this structure that you see here highlighted in green, the medial geniculate nucleus of the thalamus, which then relays it to the primary auditory cortex in the temporal lobe. This way, the inferior colliculus will play a role in auditory processing.
Next structure I’m going to be highlighting here is known as the quadrigeminal plate. Now, the inferior and superior colliculi together they form this structure. Now, the quadrigeminal plate which is also referred to as the tectum, or the midbrain tectum, is the dorsal part of the mesencephalon, or the midbrain, and is responsible for auditory and visual reflexes.
Next structure we’re going to be highlighting is then known as the midbrain tegmentum. The ventral part of the midbrain is then called the tegmentum. The tegmentum includes different structures such as the mesencephalic part of the reticular formation, the red nucleus, the substantia nigra, and the cerebral peduncles. Additionally, in the midbrain tegmentum, we find the nuclei of the oculomotor nerve and also from the trochlear nerve.
Next structure we’re going to be highlighting here is known as the cerebral aqueduct, also known as the mesencephalic aqueduct or the aqueduct of Sylvius. The structure is located in the midbrain or mesencephalon. It is a canal that connects the third ventricle and the fourth ventricle of the brain. Now as I move here to this illustration with the ventricles of the brain, you notice that the cerebral aqueduct is located right in the border of the dorsal part of the midbrain tectum with the ventral part of the midbrain, the tegmentum. It is filled with cerebrospinal fluid, CSF, and the narrowing of this canal, for example, in aqueducts stenosis can obstruct the flow of CSF.
Next structure we’re going to be seeing here, the pons. This is a part of the brainstem located in the front of the cerebellum which we also see here – this is the cerebellum, a cut of the cerebellum. It is found between the midbrain and this other structure here, the medulla oblongata – so midbrain and medulla oblongata. It consists of crossing fibers and cells from the cerebral pontine and cerebellar tract. In addition, the pons is connected to the cerebellum via the cerebellar peduncles. Now, the nuclei of the following cranial nerves are located in the pons. I will show you some images and see these cranial nerves here and the nuclei. We’re going to then highlight them to just give you an idea which ones are located in the pons.
So, the first one you see here on the far left, this is the pontine nucleus of the trigeminal nerve CN V, so this is a sensory nucleus. Also, here, we find then the motor nucleus of the trigeminal nerve highlighted in green and the abducens nucleus or the nucleus of the abducens nerve. We also find these other nuclei and structures here in the pons. On the far left, we find then the facial nerve nucleus, the vestibulocochlear nuclei specifically the vestibular nuclei, and the two cochlear nuclei as you can see here on these two images showing the two cochlear nuclei.
Next, we’re going to be seeing here below this structure that I mentioned before, this one is the medulla oblongata. So immediately inferior to the pons, we see this last part of the brainstem. Now, it begins at the lower margin of the pons at the pontomedullary junction up to the root fibers of C1. The medulla oblongata deals with autonomic functions such as breathing, heart rate and blood pressure. Please note that the medulla oblongata contains the cardiac, respiratory, vomiting and vasomotor centers. We will not discuss the tracts and nuclei found on the medulla on this tutorial as it will be covered on a separate one.
The next structure that I also pinpointed before, this one highlighted in green is the cerebellum. Now that we have covered all the structures of the brainstem that we can see in this mid-sagittal view of the brain, I wanted to take a look at another two structures that lie behind the brainstem starting with this one which is then the cerebellum. Now, in this illustration, we see the cerebellum is located just inferior to the occipital lobe of the brain behind the brainstem in this area here, the cerebellar fossa in your skull – this is where the cerebellum will then be placed in your skull.
Now, the name cerebellum comes from the Latin word meaning small brain. It plays an important role in motor control and is composed of various parts. We will not go into detail about the parts and functions of the cerebellum as we have done it already on a separate tutorial which you can find now here at Kenhub.
Finally, the last structure we’re going to be talking about – this one here – the final structure we’re going to look at seen from the medial view of the brain is the fourth ventricle. It is one of the four fluid-filled cavities ventricles of the brain. It is filled with cerebrospinal fluid and extends from the cerebral aqueduct to the obex which is the most caudal point in the fourth ventricle and it is the point where this ventricle narrows to become the central canal of the spinal cord.
The roof of the fourth ventricle is located on its dorsal surface and is formed by the ventral surface of the cerebellum, specifically the superior and inferior medullary velum. Now, the floor of the fourth ventricle is formed by the rhomboid fossa, which is highlighted in green on this image of the dorsal view of the brainstem, and also formed by the cerebellar peduncles as you can see here highlighted on all these three images – the inferior, the middle and superior cerebellar peduncles.
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Now, good luck everyone, and I will see you next time.