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Medial view of the brain

Structures seen on the medial view of the brain. The images show a midsagittal section of the brain.

Your first video. Move on to the quiz below to solidify your knowledge



Remember when you first started learning neuroanatomy and it was so simple with structures like the cerebrum, the cerebellum, and maybe you'd even talk about the brainstem. That was nice, wasn't it? But, then, someone decided to split it open and all of this stuff came out. I'm with you. It’s a lot to learn, but stick with me throughout this tutorial where we'll break it all down and you'll come out a pro, ready to ace your next neuro exam.

Welcome to our tutorial on the midsagittal view of the brain.

So, this is the image that we're really going to get familiar with today, and to see this view of the brain, we've taken a full brain, like this one on the right, which we can now see from an inferior view. And from here, we've cut the brain into two equal halves right down the midsagittal plane, and this plane is already marked naturally by the longitudinal fissure.

As I just mentioned, this is the image we'll be focusing on for most of the tutorial as well identify all the bits and pieces that make up the brain from a midsagittal view. As we identify these structures, we'll stick to an order something like this. First up, we'll make sure we can identify the main sections of the brain and some are easy to identify from the lateral view, but maybe a bit less familiar from this perspective. And these are the cerebrum, the diencephalon, the brainstem, and the cerebellum.

Then we'll break down each of these sections to identify all of the lobules, sulci, glands, ventricular components, and more, and this will include identifying the Brodmann areas that are visible from the midsagittal view. We’ll also look at the ventricular system of the brain including some ventricles themselves, their boundaries, and the circumventricular organs. And, finally, we'll discuss a clinical scenario relevant to what we've learned in our clinical notes.

First up, let's do a quick review of the main sections of the brain. So, highlighted in green on your screen is the largest part of the brain and this is part of the cerebrum, specifically, the right hemisphere. The cerebrum is made up of the right and left hemispheres which are separated by the longitudinal fissure and, within the right cerebral hemisphere, we can identify many lobes, lobules, sulci, and gyri that are present in both hemispheres. So, remember, whatever we see in this image of the right hemisphere will also exist in the left hemisphere.

So tucked sort of within the cerebrum is the diencephalon, and the diencephalon is composed of various structures including the thalamus and the hypothalamus – both of which we'll discuss later on in this tutorial. And the diencephalon is also where we'll find two endocrine glands, a structure that connects the right and then left thalami, and more. Immediately inferior to the diencephalon is the brainstem, and the brainstem is made up of the midbrain, the pons, and the medulla oblongata. Posterior to the brainstem is where we find our final section of the brain – the cerebellum.

Okay, so now that we're familiar with the main sections of the brain, let's break them down into their smaller parts, and we'll start with the cerebrum.

The cerebrum is divided into six lobes, five of which we can see in this midsagittal cut. The first is the frontal lobe, which is the largest part of the cerebral hemisphere. It is separated from the parietal lobe by the central sulcus and contains the primary motor cortex which controls voluntary movements. Posterior to the frontal lobe is the parietal lobe and this lobe contains the primary sensory cortex and is also part of the language processing network of our brains.

Right at the very posterior aspect of the brain is where we find the occipital lobe, and the occipital lobe contains the primary visual cortex. The inferior aspect of the cerebral cortex is where we find the temporal lobe in this view and, since we're looking at it from a medial perspective, do note that much of it is blocked by the brainstem. In this image, we can see more of the temporal lobe which contains the auditory cortex and the ability to comprehend language.

The final lobe that we can see from this angle is the limbic lobe now highlighted in green, and the limbic lobe is involved in many functions such as the modulation of emotions and learning and memory. The sixth lobe is called the insula, and the insula is found deep to the lateral fissure and lies between the frontal and temporal lobes. And we can't see it from the midsagittal view of the brain, so we won't be covering it in this tutorial.

So, another way to organize the brain is through this map showing what are called Brodmann areas, and these areas of the cerebral cortex are defined by its cytoarchitecture rather than by lobes, gyri, and sulci. Cytoarchitecture looks at histological structure and cellular organization and we'll have a look at what Brodmann areas corresponds to various structures we identify as we look at the features of the cerebral cortex.

So, let's go back to the frontal lobe and identify some specific parts with it. So we're going to begin with the anterior most feature of the frontal lobe, and in this lobe, we can see highlighted in green, the medial frontal gyrus. As I mentioned, this structure is part of the frontal lobe of the brain and it's a continuation of the superior frontal gyrus as seen on the medial surface of the frontal lobe, and it’s part of the prefrontal cortex and is responsible for focusing on tasks. The medial frontal gyrus contains parts of four different Brodmann areas. At the posterior aspect of the medial frontal gyrus is Brodmann area six, and area six is the premotor and supplementary motor cortex.

Moving anteriorly, we come across area eight, which is part of the motor association cortex. Area nine is here and is the dorsolateral/anterior prefrontal cortex, and, finally, area thirty-two sits underneath as the dorsal anterior cingulate cortex. We can see each of these Brodmann areas contributing to the medial frontal gyrus, showing this gyrus contains four distinct cytoarchitectural areas. Marking the posterior border of the medial frontal gyrus is the paracentral sulcus, and at this point, we're still in the frontal lobe, but getting closer to the parietal lobe.

The next structure we’ll look at is found just posterior to the medial frontal gyrus and is called the paracentral lobule. The paracentral lobule is the convolution at the medial hemispheric surface which connects the medial portions of the precentral gyrus and the postcentral gyrus. Since this lobule sits immediately posterior to the medial frontal gyrus, its anterior border is the sulcus we just identified – the paracentral sulcus.

So this lobule that we're going to be looking at right now contains five distinct Brodmann areas. That seems like a lot for such small area, right? But these Brodmann areas will continue laterally to the part of the cortex that we can't see from this view. And the area that makes up the bulk of the paracentral lobule is area four – and this area is the primary motor cortex. Posterior to this are three areas – three, one, and two – and these three areas are the primary somatosensory cortex.

Immediately inferior to them is area five which is the somatosensory association cortex and, in this case, these Brodmann areas fit quite nicely into the lobule shape. Posteriorly, the paracentral lobule is bordered by the sulcus we can see highlighted now, and this is the marginal sulcus. So can you tell me what lobe do you think we're in now? So, we've moved posterior enough now to be in the parietal lobe, but do you know where the change happened?

So the frontal and parietal lobes are divided by this sulcus called the central sulcus, and from this midsagittal section or medial view of the brain, it doesn't really look like a big enough feature to divide these two major lobes, but from this lateral view of the brain, we can see this large sulcus between the frontal lobe here and the parietal lobe here. So if we quickly peek back at the paracentral lobule highlighted again here in green, can you identify the central sulcus? That’s right, it's within the paracentral lobule over here. The paracentral lobule surrounds the medial end of the central sulcus and, because of that, it’s part of the primary motor cortex and the primary somatosensory cortex, controlling both motor and sensory innervation of the contralateral lower extremity.

Next up, moving posteriorly still is the precuneus. So, immediately posterior to the paracentral lobule is where we can find this structure and the precuneus is part of the parietal lobe and is located posterior to the marginal sulcus. And this structure is still within the parietal lobe, however, it is the most posterior part of that lobe. Within the precuneus, we mostly find parts of two Brodmann areas – area seven and thirty-one – and in this case though, area thirty-one, in particular, extends beyond the boundaries of the precuneus. Area seven is the somatosensory association cortex while area thirty-one is the dorsal posterior cingulate cortex.

Next, we'll talk about the parietooccipital sulcus, which is the posterior border of the precuneus. As the name suggests, it marks the boundary between the parietal lobe and the occipital lobe. So if this next structure is behind the parietooccipital sulcus, it must be part of the occipital lobe and this structure is known as the cuneus.

The cuneus is also bordered by the calcarine sulcus which you can see over here. The cuneus, being part of the occipital lobe, is involved in the visual pathway, and we'll see its associated Brodmann areas are those visual cortices. The cuneus contains part of areas seventeen, eighteen, and nineteen. Area seventeen, the most inferior, is the primary visual cortex; and moving superiorly, area eighteen is the secondary visual cortex; and, finally, area nineteen is the associative visual cortex.

Within the line of the cuneus boundaries drawn in, we can see it contains only part of area seventeen – the primary visual cortex – but is completely full of the various other visual cortices. To highlight again, the calcarine sulcus is located here in the occipital lobe below the cuneus, and it meets the parietooccipital sulcus at an acute angle anteriorly.

Moving anteriorly, we can see a long sulcus running beneath the frontal lobe and this is the cingulate sulcus. Posteriorly, this sulcus is continuous with a sulcus we identified earlier – and do you remember what it's called? The marginal sulcus.

The next structure we're going to be highlighting is called the cingulate gyrus, and this is another important part of the cerebral cortex that is seen on the medial aspect of the cerebral hemispheres. The cingulate gyrus is located between the cingulate sulcus and the sulcus of the corpus callosum, and the cingulate gyrus is part of the limbic system and located in the limbic lobe and it's involved in many higher cognitive functions including memory and emotional response.

As this cingulate gyrus is such a large structure, it, as you may expect, has a lot of Brodmann areas within it and we're going to be looking at six of them in this image now. So, starting anteriorly and moving back, we first have area twenty-five, which is part of the infralimbic cortex. Next, we can see area twenty-four with thirty-three stuck beneath it, and over here, we can see twenty-three and thirty, which are all part of the anterior cingulate cortex, and, finally, caudally is area twenty-nine, which is part of the posterior cingulate cortex. And several of these areas extend out with the cingulate gyrus again not sticking to the sulci boundaries that are labeled based on their cytoarchitecture.

And before we move on, just note that we haven't covered all of the Brodmann areas here – only the ones that we can see from a midsagittal view of the brain.

Just below the cingulate gyrus, we can see the sulcus of the corpus callosum which takes its name from the largest commissure of the brain that lies below it – the corpus callosum. So let's have a look at this massive commissure – the corpus callosum.

So this structure is located at the base of the longitudinal fissure of the cerebrum which you can also see here on this image. So in this image on the right, two cuts have been made – a transverse cut and a coronal cut – and part of the corpus callosum has been removed, but you can see the anterior portion of it exposed and highlighted. The longitudinal fissure is over here and you can see if we keep moving inferiorly, eventually we'll hit the corpus callosum. Therefore, to get this midsagittal view, we've actually cut right through the corpus callosum.

So the corpus callosum is the largest commissure of the brain comprising of massive transverse fibers connecting the left and right cerebral hemispheres, and you can see perfectly on this image how the corpus callosum is connecting the right and left cerebral hemispheres.

As I mentioned just now, the corpus callosum is the largest commissure of the brain, but there are four more commissures that are visible in this midsagittal section of the brain. And here you can see one of these commissures, which is called the anterior commissure. The anterior commissure also connects the left and right cerebral hemispheres and it specifically connects the inferior parts of the temporal lobe and the anterior olfactory areas of both sides.

Another band of nerve fibers that crosses the midline is the posterior commissure which we can see more posteriorly now highlighted in green. So, the posterior commissure is still a little bit of a mystery in humans. We don't know too much about it, but it has some small nuclei associated with it and contains fibers from several other structures such as the superior colliculi. And don't worry I'll tell you what the superior colliculi are in a little while.

The third of the additional four commissures that we can see in this plane is the habenular commissure. So this commissure connects the habenular nuclei on both sides of the diencephalon, and these nuclei receive fibers from parts of the limbic system, the amygdala, and the hippocampus, but their exact function is unknown to us.

The final commissure that we can see from this midsagittal cut of the brain is called the fornix. And this structure is made up of a curved bundle of nerve fibers that pass in both directions and connects the hippocampus with the mammillary bodies as well as some other nuclei, and the fornix is the main efferent system of the hippocampus.

Okay, so, wow, we've really covered a lot, haven't we?

So far, we've identified the structures of the cerebral hemispheres that are seen in the midsagittal cut of the brain as well as the five major commissures visible in this plane. Some of these commissures were part of the diencephalon, so what do you say we finish up with some other structures in that same area.

Okay, so, one of the main parts of the diencephalon are the right and the left thalami. So we can see them highlighted in this image of the brain from a superior view and, in this image, we've made a coronal and a transverse cut to reveal the internal structures of the brain. From this midsagittal view, we can see part of the right thalamus making up the lateral wall of a space called the third ventricle, and if we looked back at the first image, we can see that there is a space between the two thalami, and if we make the sagittal cut right down the middle of the brain, we're actually completely missing the thalami. So this wall of the ventricle that we can see is actually more lateral than the midsagittal cut that we've made.

So the area we can see highlighted, however, is filling the space overlying the thalamus, and we’ll visit this space – the third ventricle – again later on when we talk about the ventricular system.

Another main component of the diencephalon is the hypothalamus. As its name suggests, this area is underneath the thalamus and it consists of a number of nuclei that control a wide variety of physiological processes such as thermoregulation, osmoregulation, and more. Similar to the thalamus, the hypothalamus is actually located lateral to the midline that we've made a cut in, also contributing to the wall of the third ventricle.

Okay, let's take a moment to talk about the mammillary bodies. So, there's a mammillary body on each side of the brain. So here we're looking at the right mammillary body, and these round elevations are on the floor of the diencephalon and are part of the limbic system.

So do you remember which structure we said attaches to the mammillary body bringing fibers from the hippocampus? Yep, you're right! That was the fornix. But the fornix doesn't look like that it joins up, does it? In this new image, much of the cerebrum has been removed and we’re left with few structures that make up the very center of the brain. This is part of the corpus callosum. The mammillary bodies are highlighted in green and we can see a structure directly attached to them now. This is the fornix. Can you see how anteriorly each fornix deviates away from the midline before coming back together at the mammillary bodies? That’s the part that we can't see in our midsagittal cut of the brain. And from a functional point of view, the mammillary bodies, with their connection to the limbic system, are related to memory formation.

Next up is another small but very important structure – the pituitary gland – and we can now see this highlighted in green. The pituitary gland is also known as the hypophysis and it's an endocrine gland that protrudes off the bottom of the hypothalamus at the base of the brain. The pituitary gland sits in the hypophyseal fossa of the sella turcica which we can see in this image on the right. And how perfect is that spot. The small pea-shaped body of the pituitary gland is comprised of an anterior lobe – adenohypophysis – and also a posterior lobe – the neurohypophysis.

The function of the pituitary gland being an endocrine gland is synthesis, storage, and secretion of hormones and the control of the hypothalamus, and some hormones it secretes are involved in controlling body activities such as blood pressure, metabolism, growth, and more.

Another structure in this part of the brain that can also be seen in this midsagittal cut is the optic chiasm. The optic chiasm is a flattened quadrangular-shaped body in front of the pituitary gland where some of the axons of the optic nerve cross to the opposite side. Specifically, axons from the nasal retina crossed to the opposite side whereas axons from the temporal retina run directly caudal without crossing. And here we can see the optic chiasm from this illustration of the base of the brain and the pituitary gland is the small bulbous structure here in the midline. And this is where the nasal part of the optic axons decussate or crossover.

So we're now going to move on to the posterior part of the diencephalon and look at another gland that you can see from this view, and this is called the pineal gland, which is also an endocrine gland, sometimes referred to as the pineal body or the epiphysis. The pineal gland is suspended from the habenula. And remember this structure over here? That’s our habenula commissure.

From this superior view where, remember we've cut away much of the cerebrum, we can see this single pineal gland in the midline. This small but important structure releases a hormone known as melatonin which is a derivative of serotonin and plays a role in the regulation of circadian rhythm.

Okay, so, the final structure we'll identify in the diencephalon for now is this small structure highlighted in green, and this is the interthalamic adhesion. The interthalamic adhesion is comprised of nerve cells and nerve fibers and, as the name suggests, it connects the left and right thalami at their medial surfaces.

Okay, so, let's move on to our third main section of the brain – the brainstem. So before we jump into the details, let's start with just the three main parts of the brainstem. So, first, most superiorly, we see the midbrain or the mesencephalon; a bit further down, you find the pons; and, finally, at the inferior end is the medulla oblongata.

We’ll take a closer look at some specific features of the midbrain that we can see from a midsagittal view, and first up is the ventral portion of the midbrain now highlighted in green, and this is the midbrain tegmentum. The midbrain tegmentum contains different structures such as the red nucleus, the substantia nigra, and the cerebral peduncles. Additionally, in the midbrain tegmentum, we find the nuclei of the oculomotor nerve and the trochlear nerve.

Next up is the dorsal portion of the midbrain and this is called the quadrigeminal plate. Also referred to as the tectum or the midbrain tectum, this dorsal part of the mesencephalon is responsible for auditory and visual reflexes. Making a part of the quadrigeminal plate are a couple of different structures and the superior most feature is a rounded projection called the superior colliculus.

So from this posterior view of the brainstem, we can see that the superior colliculus is a paired structure with one on either side of the midline. Together, they surround the inferior part of the pineal body which we can see here in the midline and the two superior colliculi are connected with the optic pathway and are involved in directing eye movement.

Immediately inferior to the superior colliculus is – as I'm sure you've guessed – the inferior colliculus, and just as with the superior one, this is also a paired structure. The two inferior colliculi are also elevations of the quadrigeminal plate, but are instead connected to the auditory pathway.

Ok, moving down along the brainstem, we now come across the pons. So, this is the part of the brainstem located in front of the cerebellum and the pons houses the nuclei of cranial nerves five, six, seven, and eight.

Last, but not least, the most inferior part of the brainstem is highlighted right now. This is the medulla oblongata. The medulla oblongata begins at the lower margin of the pons at the pontomedullary junction up to the root fibers of spinal nerve C1, and the medulla oblongata processes autonomic functions such as breathing, heart rate, and blood pressure. Additionally, it contains the cranial nerve nuclei nine to twelve.

And, finally, one last main section to go – the cerebellum. The cerebellum lies behind the brainstem specifically lying posterior to this part here, the pons. And in this illustration we can see that the cerebellum is located just inferior to the occipital lobe of the brain. The name cerebellum comes from the Latin word meaning ‘small brain’ and plays an important role in motor control.

The last section of this tutorial will span across a few regions of the brain looking at the components of the ventricular system, and this should also help us review some of the structures that we've looked at today.

The ventricular system is a set of four interconnected cavities or ventricles in the brain where the cerebrospinal fluid is produced. In this midsagittal cut of the brain, we've opened up the brain right through the third ventricle, and this ventricle is a single unpaired space situated between the right and left thalamus. And just note that we've skipped the first two ventricles of the brain – the lateral ventricles – as we can't see them from this perspective.

Hanging from the root of the third ventricle is a structure called a choroid plexus, and this is one of the structures of the brain where cerebrospinal fluid is produced. And there are four choroid plexuses, one in each ventricle of the brain. And other than production of CSF, the choroid plexus also acts as a filtration system.

Running inferiorly from the third ventricle is this thin channel called the cerebral aqueduct, also known as the mesencephalic aqueduct or aqueduct of Sylvius. And can you identify which part of the brain this structure is located in? Yep, it's located in the midbrain. In this midsagittal cut, the cerebral aqueduct can be used as a landmark to separate the midbrain into its ventral midbrain tegmentum and dorsal quadrigeminal plate. As part of the ventricular system, it is a canal that connects the third ventricle and the fourth ventricle of the brain and, of course, therefore, is filled with CSF.

Inferiorly, the third ventricle is continuous with the structure highlighted now via the cerebral aqueduct and this is the fourth ventricle. The fourth ventricle also contains CSF and it extends from the cerebral aqueduct to the obex. The obex 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.

Okay, so now that we've identified the main large ventricular spaces seen in the midsagittal cut, we'll take a closer look at specific features in the walls and the boundaries of these spaces. So, let's move back up to the third ventricle specifically looking at its anterior aspect. So, highlighted in green now is the supraoptic recess, also known as the optic recess. As you can see in this illustration, this small angular recess is located above the optic chiasm which is how it gets its name, supraoptic.

Now in this image, we can see another recess of the third ventricle highlighted in green – the infundibular recess. And as its name suggests, it is located in the infundibulum of the third ventricle. As you can see a bit more clearly here in this illustration, the infundibular recess is located caudal to the supraoptic recess and forms the median eminence in which the stalk of the pituitary gland is attached.

Next up is the structure highlighted now called the lamina terminalis, and the lamina terminalis is a thin wall forming the anterior border of the third ventricle of the brain and it's connected at its superior end with the rostrum of the corpus callosum. Inferiorly, we can see its relationship to this recess here and, if you remember, this is the supraoptic recess.

The next structure we're going to look at is located between the corpus callosum and the fornix and this is the septum pellucidum. It is a thin bilayered triangular plate that separates the anterior horns of the left and right lateral ventricles of the brain from one another.

Moving back now to the fourth ventricle, we can see this structure on its superior aspect highlighted in green called the superior medullary velum. The superior medullary velum is a thin layer of tissue making up the superior border of the fourth ventricle and, in this image on the right, we're looking at the cerebellum from an anterior view. We can see the superior medullary velum spanning across the midline forming that superior border of the fourth ventricle.

And as I'm sure you've probably guessed, the inferior border of the fourth ventricle is called the inferior medullary velum and we can see it now highlighted in green. Again looking at the anterior view of the cerebellum, we can see the inferior medullary velum spanning the midline to form that inferior border.

Within the ventricular system at certain points in the walls, there are specialized cells that form structures called the circumventricular organs. In general, these areas are characterized by an absence of the blood-brain barrier so provide locations for particular hormones producing the brain to enter the circulation and they also act as sensory organs detecting the levels of various substances in the brain to trigger changes in brain function.

So, the first circumventricular organ that we'll look at is found in the floor of the fourth ventricle, and this is the area postrema which is an important chemoreceptive area and it detects substances in the blood that will then lead to vomiting.

Moving up to the third ventricle, another circumventricular organ is highlighted now. So, do you remember the structure up here that it seems to be associated with? Yep, that's the lamina terminalis. So this organ is called the vascular organ of lamina terminalis. Nice and easy, right? And this organ is involved in regulating fluid balance.

At the posterior aspect of the third ventricle just before the cerebral aqueduct is where we find the subcommissural organ. As its name suggests, it is located below this structure here – the posterior commissure. And the subcommissural organ secretes proteins that are involved in various aspects of neurogenesis.

The last circumventricular organ that we'll look at is highlighted now and this is the subfornical organ, and its name gives us a clue as to what structure it's sitting beneath. Yes, it's the fornix. And this is close to the interventricular foramina which connects the lateral ventricles to the third ventricle. The subfornical organ is involved in regulating fluid volume and thirst.

Okay, so we've finished all the things that we want to look at in our midsagittal part of the brain, and now that we know what the brain looks like from this view, can you identify what's unusual about this image? What’s the abnormal component? That’s right. It’s this structure here sitting within the third ventricle. This is a colloid cyst. Colloid cysts are fluid-filled sacs forming within the ventricles of the brain. The danger of this particular one is that it is blocking the flow of CSF from the lateral ventricles into the third ventricle, and these growths are benign, but can cause headaches and memory loss.

These cysts are usually diagnosed by medical imaging of the brain such as a CT scan or MRI, and to treat symptomatic cysts, many can be removed by endoscopic surgery or, in some cases, ventricular shunts may need to be put into place to allow CSF to bypass the blockage. And now you're totally an expert on the brain from the midsagittal view.

Before I let you go, let's have a quick review of what we looked at today.

So we began by looking at the cerebrum and its macroscopic components of specific gyri and sulci. We also related some of these gyri to Brodmann areas which are classified based on their cytoarchitectural structure. Beginning anteriorly, we identified the medial frontal gyrus as this large gyrus here, and this gyrus contains parts of Brodmann areas six, eight, nine, and thirty-two. Posteriorly, it's marked by the paracentral sulcus and posterior to that is the paracentral lobule, which connects the precentral and postcentral gyri, and this small lobule contains Brodmann areas four, three, one, two, and five.

Marking the posterior boundary of the paracentral lobule is this sulcus here – the marginal sulcus – and within the paracentral lobule is another sulcus called the central sulcus. This is the marker for where the anterior frontal lobe ends and where the more posterior parietal lobe begins. Within the parietal lobe now is the precuneus and this contains parts of the Brodmann areas seven and thirty-one.

Marking the posterior boundary of the precuneus as well as the transition from the parietal lobe to the occipital side is the parietooccipital sulcus, and within the occipital lobe is where we find the cuneus. Containing parts of Brodmann areas seventeen, eighteen, and nineteen, the cuneus makes up part of the visual cortices.

Lastly, in the occipital lobe, we see this boundary of the cuneus here which is called the calcarine sulcus and running underneath the frontal lobe and continuous with the marginal sulcus is the cingulate sulcus. Underneath the cingulate sulcus is this large gyrus here – the cingulate gyrus – and this gyrus is part of the limbic lobe and contains parts of Brodmann areas twenty-five, twenty-three, twenty four, thirty, thirty-three, and twenty-nine.

Between the cingulate gyrus and the corpus callosum is where we find the sulcus of the corpus callosum and here is that large commissure itself - the corpus callosum – which connects the right and left cerebral hemispheres.

Next up, we looked at four other commissures that we can see in this midsagittal view. Firstly, we looked at the anterior commissure connecting parts of the left and right temporal lobes to each other. Posteriorly, we looked at the posterior commissure which is still a bit of a mystery to us. The third commissure we saw was the habenular commissure connecting the habenular nuclei to the diencephalon and, finally, we looked at the fornix which connects the hippocampus and the mammillary bodies.

Next up, we moved to the diencephalon to finish identifying the structures there, and first we looked at two of the main components of the diencephalon that a lot of these other structures are related to. The thalamus makes up the lateral wall of the third ventricle in this area and the hypothalamus also contributes to the lateral wall of the third ventricle here underneath the thalamus.

We then looked at the mammillary bodies and these rounded elevations are on the floor of the diencephalon and they're part of the limbic system and one of the endocrine glands that we looked at is highlighted now – the pituitary gland. Superior to the pituitary gland is the optic chiasm, the point at which some of the optic nerve fibers crossover to the other side of the brain and, posteriorly, we saw another gland, the pineal gland, which helps us to regulate our sleep pattern. And the final structure of the diencephalon we looked at is the interthalamic adhesion which connects the left and right thalami.

We then moved on to another main section of the brain, the brainstem, and we started at the superior end with the midbrain and the anterior part of the midbrain is the midbrain tegmentum and the posterior part is the quadrigeminal plate. Within the quadrigeminal plate is this superior elevation, the superior colliculus, and inferior to that is the inferior colliculus. The remaining two parts of the brainstem are this rounded portion here, the pons, and most inferiorly, the medulla oblongata. Finally, the last main portion of the brain that we identified was the cerebellum which is highlighted now.

The last section that we worked through in this midsagittal view of the brain was the ventricular system, and, first, we saw the third ventricle in the center of the brain and within the third ventricle, we found the choroid plexus of the third ventricle which produces cerebrospinal fluid. Inferiorly, the CSF in the third ventricle drains through the cerebral aqueduct and that cerebral aqueduct connects the third ventricle to this section here, the fourth ventricle.

Within the ventricles, we identified various boundaries and recesses including this supraoptic recess superior to the optic chiasm. Caudal to the optic chiasm is the infundibular recess at the infundibulum of the third ventricle. And making up the anterior border of the third ventricle is the lamina terminalis, and superiorly, we found the septum pellucidum which separates the anterior horns of the lateral ventricles.

Inferiorly, lining the fourth ventricle anterior to the cerebellum, we identified a couple of other boundaries and this one is the superior medullary velum making up the superior boundary of the fourth ventricle and, over here, we can see the inferior medullary velum which is the inferior boundary of the fourth ventricle.

Finally, we looked at some structures within the walls of the ventricles called circumventricular organs. First, we saw the area postrema in the floor of the fourth ventricle, and then we saw the vascular organ of the lamina terminalis which is involved in regulating fluid balance. Inferior to the posterior commissure is the subcommissural organ and, finally, we identified the subfornical organ beneath the fornix.

Lastly, we had a quick look at colloid cysts in the third ventricle including symptoms, diagnosis, and treatment options.

And that brings us to the end of the tutorial on the midsagittal section of the brain. I hope you enjoyed it. Thanks for joining me. Happy studying!

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