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Arteries of the brain

Arteries of the brain seen from the lateral and medial views of the brain.

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Transcript

Hello everyone! It's Megan from Kenhub here, and welcome to our tutorial about the arteries of the brain where we'll focus primarily on images that illustrate lateral and medial views of the brain. So let's get familiar with these images before we go any further.

Here we can see a lateral view of the brain in isolation, specifically, we're looking at the brain from the left-hand side. If we sliced down the midline of our brain with a scalpel, we can see a medial view of the brain and its internal structures. We'll also cut away the brainstem and the cerebellum so that we can see the cerebrum on its own.

Okay, so now we're familiar with our two key images – the medial view on the left and the lateral view on the right. Another image that we'll see occasionally is this one here where we can see an inferior view of the brain or the brain as viewed from below.

Now that we're comfortable with the images that we'll feature throughout this video, let me give you a quick overview of what we'll discuss during this tutorial.

Arterial blood supply to the brain is very important because it maintains brain function which in turn governs all other bodily functions. The arterial supply to the brain can be divided into arteries responsible for anterior circulation and arteries responsible for posterior circulation. Arteries responsible for anterior circulation arise from the internal carotid arteries and those responsible for posterior circulation arise from the vertebral arteries. So, we'll kickstart this tutorial with the anterior circulation of the brain which, of course, starts with the internal carotid arteries.

The internal carotid arteries arise in the neck from the common carotid arteries and we can see them in situ in our lovely lady here. They then travel superiorly to the base of the skull and enter the cranial cavity through the carotid canals in the temporal bones. Within the cranial cavity, the internal carotid arteries give off several branches including the anterior cerebral artery, the middle cerebral artery and the posterior communicating artery.

Let's zoom in on our lady even further so that we can see some of the vessels I've mentioned a little bit more clearly. So, first, I'll label the common carotid artery which gives rise to the internal carotid artery that we can see highlighted in green. It also gives rise to another artery called the external carotid artery.

Now that we've seen how the internal carotid artery looks in situ, let's move on to a medial view of the brain where we can see the right internal carotid artery highlighted in green. The key part to remember here is that the internal carotid artery gives rise to branches responsible for the anterior circulation of the brain. The first branch of the internal carotid we'll look at today is the anterior cerebral artery.

The anterior cerebral artery rises from the internal carotid artery at the anterior perforated substance which I've marked for you with a blue cross on your screen. It then passes anteriorly above the optic chiasm into the medial longitudinal fissure. The reason we're viewing the brain from below here is because the anterior cerebral artery contributes towards the circle of Willis, which is an interconnected ring of arteries located at the base of the brain. The circle of Willis functions to provide multiple pathways for oxygenated blood to supply the brain if any of the arteries are constricted. We'll go into more details of what happens when these blood vessels are constricted in our clinical notes.

If we cut down the midline of our brain, we can see the anterior cerebral artery from a medial view. Specifically, we can see the right anterior cerebral artery. This artery supplies the middle surface of the cerebrum above the corpus callosum which I've labelled for you in blue and the orbital part of the frontal lobe. It then extends to meet the area supplied by the middle cerebral artery which is another branch of the internal carotid artery that we'll discuss later on in this tutorial. The anterior cerebral artery gives off several branches. The first one we're going to talk about is the anterior communicating artery.

The anterior communicating artery is a very short artery and as I just mentioned, it arises from the anterior cerebral arteries. In other words, this small artery connects the right and left anterior cerebral arteries, hence, closing up the circle of Willis anteriorly. So here we have the right anterior cerebral artery and the left anterior cerebral artery and between them highlighted in green, we can see the anterior communicating artery.

Now, let's have a look at this artery from a medial view. I've circled the tiny artery in blue for you on your screen. It's worth noting here that the anterior communicating artery is one of two unpaired arteries that we'll talk about today. The rest of the arteries we'll see are paired and that there's a right one and a left one. The next branch of the anterior cerebral artery we'll look at is the medial frontobasal artery. This artery courses on the medial aspect of the cerebral hemisphere to the frontal pole where it goes on to supply the orbital part of the frontal lobe.

Another artery that arises from the anterior cerebral artery just after the medial frontobasal artery is the polar frontal artery. As you can see, this artery runs on the medial surface of the cerebral hemisphere and goes to the frontal pole of the frontal lobe which I've labelled for you in blue. In the next illustration, we can see an artery passing over the superior surface of the corpus callosum. This artery is called the pericallosal artery. The pericallosal artery is a continuation of the anterior cerebral artery and it gives off several branches along its course which supply the corpus callosum. It also supplies other regions of the brain, for example, the precuneal branches of the pericallosal arteries supply the inferior part of the precuneus.

Another artery that arises from the pericallosal artery is the callosomarginal artery. This artery which is also known as the median artery of the corpus callosum runs parallel to the pericallosal artery in the cingulate sulcus. It's the largest branch of the pericallosal artery and it supplies the frontal lobe, the anterior parietal lobe and the paracentral area. Some of the branches that arise from the callosomarginal artery are the cingular branches, which are terminal branches of this artery. We can see these branches highlighted in green in our image on the right.

As well as giving off the cingular branches, the callosomarginal artery also gives rise to the paracentral artery which we can see highlighted in green on our image here. This artery goes to the paracentral area of the cerebrum and supplies the superior parts of the precentral gyrus and the postcentral gyrus.

Now that we're finished discussing the branches of the anterior cerebral artery which is the branch of the internal carotid artery, it's time to look at the middle cerebral artery. To do this, we're going to flip our brain so we can see the lateral surface.

The middle cerebral artery is the second largest and most direct branch of the internal carotid artery. It functions to supply the insular cortex which we can see here situated deep to the lateral sulcus which is being pulled apart in our image. So, first, we're going to look at the superior and inferior terminal branches of this artery. We can see the superior terminal branch here and the inferior terminal branch here. Most of the branches of the middle cerebral artery that we'll look at arise from either one of these two terminal branches. An artery that arises from the superior terminal branch of the middle cerebral artery is the lateral frontobasal artery, seen here from a lateral view of the brain. This artery supplies the frontal lobe, the inferior frontal gyrus and the middle frontal gyrus.

Let's look at another branch of the middle cerebral artery which is known as the artery of the prefrontal sulcus. This artery also arises from the superior terminal branch of the middle cerebral artery and its branches supply the inferior and middle frontal gyri. I'll show you these structures just now – so here we have the inferior frontal gyrus and here we can see the middle frontal gyrus.

Next, we have the artery of the precentral sulcus which is also known as the pre-Rolandic artery. It arises from the superior terminal branch of the middle cerebral artery and courses from its origin over the cortex to supply the precentral sulcus on either side. The central sulcus of the cerebrum is a fissure on the lateral surface of the cerebral hemisphere that separates the frontal lobe from the parietal lobe. The artery that supplies this area of the brain is aptly known as the artery of the central sulcus. This artery arises from the superior terminal branch of the middle cerebral artery and as I've just mentioned, it supplies the area of the central sulcus. You may come across the artery of the central sulcus being referred to as the Rolandic artery.

Now let's have a look at the branches that arise from the inferior terminal branch of the middle cerebral artery. The anterior temporal artery is one of three temporal branches that arises from the inferior terminal branch. After the anterior temporal artery arises, it courses out of the lateral sulcus. Here you can see the artery exposed as the lateral sulcus is separated out. The areas that this artery supplies are the anterior one-third of the inferior, middle and superior temporal gyri. So here we have the superior temporal gyrus, the middle temporal gyrus and the inferior temporal gyrus.

The second temporal branch that arises from the inferior branch of the middle cerebral artery is the middle temporal artery. This artery supplies the part of the temporal lobe located between the anterior and posterior temporal arteries. I've highlighted this region for you in blue.

The third and final temporal branch of the middle cerebral artery is the posterior temporal artery. This branch also arises from the inferior branch of the middle cerebral artery and supplies the lateral surface of the posterior temporal lobe. The middle cerebral artery also gives off a branch that supplies the angular gyrus. Of course, this artery highlighted in green, is appropriately named the branch of the middle cerebral artery to the angular gyrus. It also arises from the inferior terminal branch of the middle cerebral artery.

Another branch of the middle cerebral artery is the anterior parietal artery which we can see here highlighted in green originating from the inferior terminal branch. This artery supplies the anterior part of the parietal lobe. The middle cerebral artery also gives rise to the posterior parietal artery which we can see here arising from the inferior terminal branch. As the name suggests, this branch of the middle cerebral artery supplies the posterior part of the parietal lobe. The middle cerebral artery also gives off frontal branches which we can see here supplying the posterior part of the frontal lobe.

Finally, let's look at the posterior communicating arteries which arise from the internal carotid arteries. These arteries form part of the circle of Willis posteriorly and give rise to perforating branches that supply part of the thalamus, the posterior parts of the optic tract, the optic chiasm, the mammillary bodies and the hypothalamus.

So now that we're comfortable with the anterior circulation of the brain, let's move on to the posterior circulation. If you think back to the beginning of our tutorial, you'll remember that the vertebral arteries give rise to branches responsible for the posterior circulation of the brain. We can see these arteries highlighted in green in our image of the inferior brain. The vertebral arteries merge to form the structure you can now see highlighted in green which is the basilar artery. The basilar artery then divides into the two posterior cerebral arteries which give off many branches that supply the posterior structures of the brain.

Now, let's have a look at the posterior cerebral arteries in a bit more detail. As I just mentioned, these arteries arise from the basilar artery and are responsible for posterior circulation of the brain. The posterior cerebral arteries supply the cerebral peduncle, the optic tract, the occipital lobe and the inferomedial surface of the temporal lobes. In the next illustration, we see the right posterior cerebral artery from a medial view of the brain. This artery also sends perforating branches to the thalamus.

Now let's look at a branch of the posterior cerebral artery which we can see here – the medial occipital artery. This artery gives off branches that supply the corpus callosum, the medial occipital lobe and the medial parietal lobe. The medial occipital artery also gives off the calcarine branch which supplies the calcarine cortex. We can see this branch highlighted in green in the image on the right.

In the next illustration, we can see another branch highlighted in green which is the dorsal branch of the corpus callosum. This branch arises from the medial occipital artery and as you've probably already guessed, it supplies the dorsum of the corpus callosum. Another artery that arises from the medial occipital artery is the parieto-occipital artery. This artery then goes on to supply the medial surface of the occipital lobe and the area of the parieto-occipital sulcus.

As we come to the end of this tutorial, I'd like to put a clinical spin on the anatomy we've learned today.

In today's clinical notes, we're going to talk about strokes. Now, we've all heard of strokes but I recon some of you don't know what they are. Simply put, a stroke is a disruption in the blood supply to the brain and there are two types of stroke, either an ischemic stroke or a hemorrhagic stroke.

An ischemic stroke is caused by a blockage that disrupts the brain's blood supply. This type of stroke is more often disabling rather than fatal as the circle of Willis provides an alternative route of blood supply to the regions supplied by the occluded arteries. Hemorrhagic strokes, on the other hand, are caused by bleeds. This type of stroke can occur as a result of an aneurysm which is a weakening in the wall of an artery causing it to bulge and burst. It can also be caused by arteriovenous malformation or as a result of uncontrolled hypertension or high blood pressure.

The symptoms of a stroke depend on the artery affected as this determines which part of the brain will be damaged on what functions may be impaired. The severity of the symptoms depends on how much damage is done to the brain. The main symptoms of a stroke include physical problems in one side of the body such as numbness or weakness, drooping in one side of the face, speech problems, visual problems, confusion and severe headaches. The management of a stroke depends on the type of stroke, the area affected and the symptoms caused.

So you'll be relieved to hear that we're almost finished. We just need to summarize what we've covered in this tutorial. So, today, we've learned that arterial blood supply to the brain can be divided into anterior circulation and posterior circulation. First, we're going to summarize the anterior circulation of the brain.

Arteries arising from the internal carotid arteries provide the anterior circulation to the brain. The arteries arising from the internal carotid artery include the anterior cerebral artery, the middle cerebral artery and the posterior communicating artery. Arteries that branch from the anterior cerebral artery include the anterior communicating artery which forms anterior boundary of the circle of Willis, the medial frontobasal artery and the polar frontal artery which supply parts of the frontal lobe and the pericallosal artery which gives off several of its own branches.

Arteries that branch from the pericallosal artery include the precuneal branches which supply the precuneus and the callosomarginal artery. The callosomarginal artery also gives off several branches including the cingular branches and the paracentral artery.

The middle cerebral artery is another main branch of the internal carotid artery. This artery gives rise to the superior and inferior terminal branches. Arteries that branch from the superior terminal branch include the lateral frontobasal artery, the artery of the prefrontal sulcus, the artery of the precentral sulcus and the artery of the central sulcus. Arteries that arise from the inferior terminal branch include the anterior temporal artery, the middle temporal artery and the posterior temporal artery as well as the branch of the middle cerebral artery to the angular gyrus, and the anterior parietal artery and the posterior parietal artery. The middle cerebral artery also gives rise to the frontal branches of the middle cerebral artery. Lastly, the internal carotid artery gives rise to the posterior communicating artery which contributes towards the circle of Willis.

Next, we'll summarize the posterior circulation of the brain. So the vertebral arteries give rise to branches responsible for the posterior circulation of the brain. They merge to form the basilar artery which then divides into the two posterior cerebral arteries which give off several branches that supply the posterior structures of the brain.

Before we moved on to look at the branches of the posterior cerebral artery, let's remind ourselves of what this artery looks like from a medial view of the brain. You can see the right posterior cerebral artery in the image on your screen highlighted in green. So as you can see, the first artery stemming from the posterior cerebral artery is the medial occipital artery. This artery gives off several of its own branches including the calcarine branch of the medial occipital artery, the dorsal branch of the corpus callosum and the parieto-occipital branch of the medial occipital artery.

So that brings us to the end of our tutorial on the arteries of the brain. It's a lot of information to take in but a great way to revise this material is to draw a full chart diagram and you can use the summary of this tutorial to help you out.

Good luck, thanks for watching and see you next time.

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