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Cerebral blood supply: Part 1

Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Vishal Punwani.

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Video transcript

- [Voiceover] Your brain is the most complicated structure in your body. It sits inside your head and it's protected, it's housed by your skull. And it's made up of these billions, and billions, and billions of neurons or brain cells. And all these brain cells, these neurons, are interconnected in this really intricate way that allow you to do things like sing and they allow you to dance, and they allow you to hear things, and to smell things, and to think and learn. So in this side view here, let me just show you the major components of the brain, the major three sections of the brain. So we have our cerebrum here, this big pink part that really is the majority of what you see when you look at a brain. That's the cerebrum, the outer part. And then in this sort of light purpley pink down here underneath the cerebrum, we have our cerebellum. And then in purple here at the very bottom, we have our brainstem. And the brainstem will eventually sort of turn into the spinal cord. So that's what it looks like from a side view, but let's look at what it looks like when it's sort of sitting in your head, in your skull. It looks kind of like that. So this is what we call an anterior view. We're looking at it from the front, anterior. So just to correlate the anterior view with the side view that we have over here, Everything that I'm outlining now in pink, that's the cerebrum. And then this light purple, this is a cerebellum down here. And then in proper purple, this is the brainstem here and you can see it sort of turns into the spinal cord nicely down below. So now that we're all acquainted with the major three components of the brain, let's further subdivide the cerebrum into its component lobes. So we have our frontal lobe here in this light blue color. And your frontal lobe is the main lobe involved in consciousness and thinking. We have our temporal lobe here in this green color. And your temporal lobe helps you with your sense of smell and your sense of sound. You have your parietal lobe here in red. And your parietal lobe is really important in helping you feel stimuli like pain and touch and vibration. And you can't really see your parietal lobe from the font view, so I'll just draw it on the side view here. And you have your occipital lobe in yellow here. And your occipital lobe is really important for your sense of sight. So let me just make it really clear that all the lobes of the brain have to work together to get their functions done. But having said that, the functions that I sort of listed earlier for each lobe, that's what that lobe sort of specializes in. So that's some really basic brain anatomy. So by now, it's really clear that the brain is really metabolically active. So it's gonna need a lot of fuel. It's gonna need a lot of glucose and a lot of oxygen. And it gets that by having a really rich blood supply. So here's a sort of a glimpse of the major arteries of the cerebrovascular system. And it looks really complicated, right? I mean, wow, there's so many blood vessels there. It's kind of a lot to take in. And it is a bit of a handful. So I find that it's easiest to look at them from the underside to learn about the different blood vessels that supply the brain. So let's look at that now. And I appreciate that it doesn't seem any easier from the underside, but we can go through it together. So let me just reiterate that the image on the right over here, we're looking at an underside view, right? So we're looking up from underneath at a brain and looking at the blood supply from underneath. And this will all sort of start to come together and make sense soon. So you just have to sort of bear with me now. So let me start by saying that although it looks really, really complicated up top, up here, all of the blood that gets to the brain is essentially coming from four major arteries initially. So you've got one here, so this is the right internal carotid artery. This is on the right side. And then you've got an internal carotid. I'll just abbreviate it ICA on the left side. That's two out of our four major arteries. Then you have this one here, which is the right vertebral artery. And then you have the left one over here. And by the way, they're called the left and right vertebral arteries because they sort of run up on either side of your spinal column, so within your vertebrae bones. And the internal carotids they run on sort of the anterior, on the front part of your neck. All right, so these are the four main arteries, the two vertebral arteries and the two internal carotid arteries, right? Left and right of each. And actually, notice that the two vertebral arteries, they sort of come together. They come together and they form this one artery here that almost looks like a little centipede. And that artery is called the basilar artery, basilar artery. So we'll actually include that as one of our major vessels as well, basilar. So let's find the same arteries over on the other view, the inferior view here. So here's your right vertebral artery. Here's your left vertebral artery. Here's your basilar artery. So that's already three out of our five major arteries. And then your internal carotids, they're actually a bit funny to find on this one. They actually end right about here. And you can see that I've sort of snipped the arteries here. And, in fact, this is right about where the internal carotid arteries end. And we'll find out what they've sort of turned in to in a few minutes here. So those are the ends of the two internal carotids. All right, now we can sort of get stuck into figuring out what all the rest of the arteries are. And, it is a really complicated sort of area, so I've always found that the easiest way to do it is to think about which artery serve the cerebrum, which artery serve the cerebelum, and which artery serve the brain stem. So let's take a look here. Let's first look at the cerebrum. So coming off, what used to be the ICA, the internal carotid, we have the creation of our new vessel called the middle cerebral artery, the MCA. So I'll draw that in here in solid. Now I'll color it in solid but then notice how it sort of dives underneath this lobe here. So we'll just do that in almost across hatched pattern. Okay. So this is the middle cerebral artery. And this is gonna serve, and remember there's one on the other side too. So I'll do it in solid here, the one that sort of dives a bit deeper into the brain's lobes will show that it's not superficial anymore. Then on the anterial view, it's a little bit tougher to see of course. But we'll do our best to draw it in. So there it is there. And it sort of heads out laterally. And it does the outside part of the brain here. Now what else serves the cerebrum? Let's actually do them all in blue here. We'll just use a different shade of blue. All the cerebral ones we'll do in blue. So the next thing that we have are the anterior cerebral arteries. And the anterior cerebral arteries supply blood to the inner parts of the frontal lobes. All right, so you can really see how the anterior cerebral artery supplies blood to the inside part of the frontal lobes. Now, we have a middle cerebral and an anterior cerebral. The only thing we're missing is a posterior cerebral. And we're actually not missing it because we're about to find it. So our posterior cerebral artery is right here. And then you can see that it sort of dives deep, sort of above the cerebellum here. So I'll just put that in in dotted, in sort of hatched lines here. And it's really a tough to see on the anterior drawing but it's about right there. So we're almost done on the blood vessels of this cerebrum. The one thing I wanna point out is that notice how the anterior cerebral vessels are connected by this little bridge here. And this bridge is called the anterior communicating artery. And notice how the middle cerebral artery and the posterior cerebral artery are joined by this bridging artery here. And there's one on each side here. And this is called the posterior communicating artery. So one thing that might become really apparent to you is now these arteries that serve the cerebrum have taken on almost a ring shape, right? There's a really obvious circle right here. And this is really important in terms of brain circulation. This circle is called the cerebral arterial circle, or the Circle of Willis if you wanna use the eponymous name. And why's that really important? Well just think about this. Let's say you get a little blockage in internal carotid here on this side. Well, you can imagine that now we're sort of restricting blood from getting up this internal carotid. Remember we said it was a major artery, the internal carotid. Blood can't enter the Circle of Willis and can't enter the middle cerebral artery from this internal carotid anymore. But because we have this collateral circulation provided by the Circle of Willis where blood can sort of go around the circle, blood can still come up from this internal carotid and get around the circle and go into the middle cerebral artery from there. >From the other side. And blood can still continue to come up these vertebral arteries and up the basilar artery and still profuse or fill up the entire circle. And thus, it really minimizes the chances of you having some type of brain injury due to lack of blood flow to a part of your brain because there's this collateral circulation, the Circle of Willis. Really important. Good, so those are the three major arteries of the cerebrum, the middle, the anterior, and the posterior cerebral arteries.