So what we're going to talk about in this video is we're going to talk about the two feeder pathways into the circular willis because there's going to be two important vessels that are going to be feeding this circular willis. One is going to be up here which is called the internal carotid artery, okay? And this is going to be feeding into the circular willis at this part. The other part that we're going to discuss is going to be down here and this is going to be the vertebra artery. That's going to feed into the back part of the circular willis. So what we're going to do is we're going to start here with the actual vertebral arteries and work our way up through the diagram annotating each individual vessel and then we'll come back and we'll talk about certain diseases that can be associated when there is occlusions of these vessels or maybe even aneurysms. Okay one more thing is just before we keep going I want to give you guys a little bit of orientation of this diagram so that we understand what we're looking at. So when you see here, this is going to be the right cerebral hemisphere, right cerebellum. This over here is going to be the left cerebral hemisphere, left cerebellum. Okay? And when we're looking at this actual circle of Willis, we're looking at it from an inferior view. Okay? Thus this annotation right there. Alright, so now let's go ahead and get started here. So first things first, we have to have these arteries right here. So you see these arteries here on the side? These bad boys right there are going to be called your vertebral arteries. You know, they're actually going to be supplied from the subclavian arteries. Now the vertebral arteries are really interesting because they actually run up through... these holes in the actual cervical vertebrae. And they call these holes the transverse foramina. But these arteries right here that are actually moving up through those transverse foramina are called the vertebral Now, the vertebral arteries, what they do is they actually run up through the transverse foramina of the cervical vertebrae. And then after that, they actually proceed before going up into the foramen magnum, they run through what's called the suboccipital triangle. And when they come up through the foramen magnum, they're going to move up like this. Okay? So now they're going to be moving up through the foramen magnum as such. As they move upwards, they give off branches here, right? This branch right here that you're going to see coming off, it's a special branch. Very, very important one. This bad boy right here is going to be called the posterior inferior cerebellar artery. So we call this the posterior inferior cerebellar artery. Okay, so that is going to be this artery right here. Okay, so posterior inferior cerebellar artery. In the same way, this one over here, I'm just going to denote it as pica, P-I-C-A, posterior inferior cerebellar artery. That is going to be this guy right there. Now, off of the posterior inferior cerebellar arteries comes these other little branches. So this branch right here and this branch right here. These guys right here are called your posterior, so they're called the posterior spinal arteries. So again, this one right here is called your posterior spinal. artery. Okay? So you have the vertebral arteries moving up. As they move up, they give off a posterior inferior cerebellar artery. And then these posterior inferior cerebellar arteries will give off these little branches here called the posterior spinal arteries. Now, the vertebral arteries will continue to move up, move up, and give off another branch. So they're gonna give off a branch here, give off a branch here. These guys will fuse together and form an artery that moves all the way down the spinal cord. This is a really important one. This guy right there is specifically called the anterior spinal artery. So this guy right here is called the anterior spinal artery. Okay? So, again, vertebral arteries, posterior inferior cerebellar arteries, off of that is the posterior spinal arteries. As the vertebral arteries move up, they give off branches that fuse together and form the anterior spinal arteries. Now, after that, here's where it gets really, really important. The vertebral arteries will come together and fuse. When they fuse, they'll move up as this big, big vessel right here in the middle. This bad boy here that's moving all the way up, the thick part here, this guy here is called the bacillar artery. Okay, that's this guy right there. So again, we have the bacillar artery, which is this guy moving all the way up here. But, as we come up here and form the bacillar artery, there's another branch that comes off. Alright? There's another branch that comes right off here. This is another really important one. They're all really important, because any type of occlusion of these vessels can cause some serious, serious diseases and syndromes. This one right here that comes off the bacillar artery here at the base, This is called the anterior inferior cerebellar artery. So this is called the anterior inferior cerebellar artery. So now as we're coming up here again we said we have the vertebrae arteries. Vertebrae arteries are going to do what? They're going to give off posterior inferior cerebellar arteries. They give off posterior spinal arteries. Then we're going to move up here, so we're moving up through the medulla, right? So this is the medulla here. We're going to come together, fuse these vertebral arteries, right? Before we fuse, they give off branches here at the medulla, which is called the anterior spinal artery. That's an important one because it does supply the pyramids here, and that moves down throughout the spinal cord. Then vertebral arteries come together, fuse, and make the bacillar artery. At the base of that bacillar artery, we have this anterior inferior cerebellar artery formed here at the level of the pons. Now we have this next one here and this is called the labyrinthine arteries. Okay so these two suckers right here are called your labyrinth, labyrinthine arteries. Okay so that's my labyrinthine artery and this is another labyrinthine artery. Okay or you can call them internal acoustic arteries. Okay then as we continue upwards throughout the pons we're gonna have all of these guys right here. These are all Pontine branches of the bacilar artery. So all of this is going to be pontine branches. So we have all of these guys up here up to the actual level of the pons now. So again we have midbrain, we have pons, I'm sorry we have medulla, pons, and then we're going to have the midbrain up here. Now as we move up past the pontine branches we give off another branch. This branch here will supply the top of the cerebellum and this sucker right here is going to be called the superior cerebellar arteries. So this right here is called my superior cerebellar arteries. Okay, so that's going to be this guy right there as well as this one over here. Now as we continue to move up at the level of this midbrain here, you're going to see that the bacillar artery is going to feed into the posterior part of this circle. We call this circle the circle of Willis. Now as the bacillar artery feeds in, it feeds into this part right here. This is actually this whole thing here from this part to this part. is our posterior cerebral artery. Okay? So this whole thing here is the posterior cerebral artery. But there's two parts of it, or two segments if you will. So let's say from here to here. This segment is called the P1 segment of the posterior cerebral artery. And then from that point here to this point here, this is the P2 segment of the posterior cerebral arteries. Okay, so again, these arteries right here, this whole one over here, if we were to write it down, this whole thing here is going to be called the posterior cerebral. Arteries. Okay, and again, this segment here would be P1, this one here would be P2. Alright, sweet deal. So we fill this posterior part of the circle of Willis. Well now, after that, look where else it can go. Now the blood can move into this next collateral channel. Because you know, the brain, the actual arteries of the brain are a great example of an arterial anastomosis. Which are just basically alternative or collateral channels for blood to flow through. And it's a beautiful thing. So now as this bacillus artery feeds into the posterior cerebral artery P1 segment it can then go up into these suckers over here on the sides. These guys here on the sides this one here and this one here this is called the posterior communicating arteries. So this is called the posterior communicating artery. Okay, same thing on that side. This would be the posterior communicating artery. Now, here's where it gets really cool. Remember I told you that the posterior part of the circle of Willis is formed by the vertebral bacillus system, right? That feeds into that part. A good 20% of the blood is from the vertebral basilar system. The remaining 80% of the blood feeding into the circle of Willis is going to be through these puppies right here. Okay, these guys right here that are really important. right here and right here. This is your right and left internal carotid artery. But again, I'm just going to write here internal carotid artery. Okay. Now the internal carotid artery, when it feeds into this, it gives off a branch first. You see this sucker right here? This guy right here is called the ophthalmic artery. We call this the ophthalmic artery. Now I like to say the H because I'm not good at spelling, so that helps me out. So the H is the H. This guy right here is called the ophthalmic artery. So this right there is the ophthalmic artery. Then, if we continue through the internal carotid artery, it's going to come out here and it's going to give off this branch over here. This is one of the big branches coming off of the internal carotid artery. That guy right there is called the middle cerebral artery. So from here to here. This entire thing here is called the middle cerebral. But why is this important? Because off of the middle cerebral artery comes some really important branches. What are some of these branches coming off the middle cerebral artery? Well, the first one is this sucker right here. That guy right there is called the anterior choroidal artery. Now this right here is called the anterior choroidal. artery. Okay? That's coming off of this middle cerebral artery. Another branches that are really important and they're going to the lenticular, the lentiform nucleus as well as some of the other structures around that is called the lenticulostriate artery. So all of these guys right here these are specifically called the lenticulostriate arteries. Okay? And again, the most important part of this one is this is going to go to the actual internal capsule as well as the lentiform nucleus with the globus pallidus and the putamen. Okay? Then after that, here's where it gets really cool. Okay. Internal carotid artery fed into this circle of oils, right? Well, then it gives off this branch that moves from here all the way here. So watch this. From this point here. And I'm going to come all the way down to about this point right here. So from this, follow it all the way up. That entire thing is the anterior cerebral artery. So what is this structure here that we said? We said from here all the way to here is referred to as the anterior cerebral artery. Now, just like the posterior cerebral artery, it's split into segments. From this point here. to about this point here. They call this the A1 segment of the anterior cerebral artery. And then from this point here to this point here, this is called the A2 segment of the anterior cerebral artery. So same thing over here, A2 segment and A1 segment of the anterior cerebral artery. Okay. Now, there's this next one right here which is so important. So important because it's so exposed. It's very, very effective in situations like barianeurysms. This sucker right here is called the anterior communicating artery. So we're going to throw this right here in the optic chiasma. So this right here, this structure. is called the anterior communicating artery. Okay? And again, that is the anterior communicating artery right there. Okay? So now, we've covered all of the important vessels of the circle of Willis. Alright, engineers, so that pretty much covers everything that you guys would need to know about the actual circle of Willis. So now what we're going to do is in the next video, we're going to start talking about certain types of clinical implications. What can happen if there's occlusions of these vessels or aneurysms? So in the next video, we're going to talk about the cerebral ischemic strokes. Okay, so I hope to see you guys there. But guys, if you guys did like this video, please hit that like button, comment down in the comment section, please subscribe. Also, if you guys get a chance, check out Facebook, Instagram, maybe even our Patreon account. All right, Ningeners, as always, until next time.