okay so this is a tutorial on The Circle of Willis so The Circle of Willis provides the blood supply to the brain and essentially what happens is that it connects two arterial sources together to form this arterial Circle which then supplies the brain with blood so the two arteries which are the source of the Circle of Willis are the internal cored arteries and you've also got the vertebral arteries as well so just rotating the model around to the lateral view you can see the vertebral arteries here coming up to supply the posterior aspect of the Circle of Willis and you can see the internal cored arteries here running up to join into the arterial Circle of Willis so just taking a look at the origin of these arteries you can see the internal cored artery rising from the common cored artery so the common cored artery Bates to the external cored and the internal cored arteries and the vertebral arteries arise from the first part of the subclavian artery so you can see that here and then they run up through the transverse Fen of the cervical vertebra so these two arterial sources Anastos to form this arterial Circle C at the base of the brain so looking at this inferior aspect of the brain I'm just going to switch over to a diagram so you can see here how The Circle of Willis is located at the base of the brain around the optic kaym and the hypothalamus so coming back to this model here I've highlighted the internal cored artery and if I rotate the model you can see how it joins this circle at the base of the brain so the internal cored artery divides to form the middle cerebral artery and the anterior cerebral artery so I've highlighted these in Orange on both sides so you can see the division into the middle cerebral artery and the anterior cerebral artery and if I rotate the model round to the lateral view you can see that the middle cerebral artery actually runs in this lateral sulcus so this this groove here which I'm outlining in green separating the frontal and parial loes above from the temporal load below is known as the lateral sulcus or lateral fissure and you can see the middle cerebral artery running within this fissure So within this fissure the middle cerebral artery gives off some small branches to supply the basil ganglia and these are called the striate arteries and just rotating the model around anteriorly you can see this fissure running down between each hemispheres and this is called the interhemispheric fissure or the medial longitudinal fissure and the anterior cerebral artery runs in this fissure so I've just removed the right Hemisphere and rotating the model round you can see the anterior cerebral artery running along in this fissure so just bringing the model back around to the inferior view you can see that there's this small connection between the anterior cerebral arteries and this is called the anterior communicating artery so it's a very short artery which connects these two together and then coming backwards off the internal cored artery you've got the posterior communicating artery which connects the internal quoted artery to the posterior cerebral AR Ary so it connects the anterior circulation provided by the internal cored artery to the posterior circulation which is provided by the vertebra basil system which I'm going to talk about next so I've just highlighted the posterior communicating arteries in Orange and you can see how they connect to the posterior cerebral arteries so another artery to mention just while we're talking about the internal cored artery is the opthalmic artery so rotating the model around you can see that the internal cored artery gives off this branch which is known as the Opthalmic artery and these arise immediately after the cored artery passes through the cavernous sinus to enter the cranial cavity so so far we've looked at the first arterial Source the internal cored artery so we've seen how it divides to form the middle cerebral and the anterior cerebral arteries and it also sends off a posterior communicating Branch to join with the posterior cerebral artery which comes off the vertebra basilis system so it's a part of the posterior circulation so before describing the vertebra basilis system I'd like to just show you the territories of the brain which the anterior the middle and the posterior cerebral arteries Supply so I've just switched over to two diagrams of the brain so the top top diagram shows the medial aspect of the brain and what it shows is that the anterior cerebral artery which is represented by the blue shaded area supplies the medial and the superior and lateral aspects of the cerebral hemisphere so the middle cerebral artery is represented in red and the posterior cerebral artery is represented by the yellow shading so if you look at the bottom diagram this shows the lateral aspect of the brain so you can see that that the lateral aspect of the brain is provided mostly by the middle cerebral artery and you can see that postery and infer the shading is yellow in both the top and bottom diagrams so the posterior cerebral artery supplies the occipital loes in the inferior parts of the brain so anterior cerebral artery supplies medial surface middle cerebral artery supplies the lateral surface mainly so just coming back to the 3D model the second source of blood is the vertebra basilis system which provides the posterior circulation so this system supplies the cerebellum the brain stem and the posterior parts of the cerebral hemispheres so the basil artery highlighted in yellow is formed by the union of the two vertebral arteries on either side so these two arteries join together at the level of the bottom of the ponds so the inferior aspect of the ponds so I've just added in the brain stem here and what you can see is the basil artery running in the midline in front of the ponds and then you can see when it reaches the midbrain it splits into the posterior cerebral arteries so the basil artery terminates by splitting into the posterior cerebral arteries so just taking a look at some of the branches of the vertebra basilis system there are three main branches which Supply the cerebellum so starting at the top you can see that there are two branches which come off either side of the basil artery just before it terminates to divide into the posterior cerebral arteries and these are called The Superior cerebella arteries so you've got Superior cerebella arteries and you've got inferior cerebella arteries at the inferior cerebella arteries you've got anterior and posterior inferior cerebella arteries so at the bottom of the basil artery you can see the anterior inferior cerebella arteries and then you've got the posterior inferior cerebella arteries which actually come off the vertebral arteries so they come off down here so as well as giving off the superior cerebella artery and the anterior inferior cerebella artery the basil artery also gives off several small pontine arteries which I've just drawn on there so we've seen that the vertebral arteries have the posterior inferior cerebella artery coming off it but it's also got two other branches so it's got the anterior spinal artery so I've just drawn that on here and you can see how it comes off the vertebral arteries to unite and form this artery which runs down the anterior median fissure of the spinal cord and similarly you've got a posterior spinal artery which runs down the posterior aspect of the spinal cord so you've got three sort of branches coming from the basil artery the superior cerebella artery the anterior inferior cerebella artery and the pontine arteries and then you got three branches which come off the vertebral arteries so the posterior inferior cerebella artery and then you've got the anterior and posterior spinal arteries so we've looked at the anterior circulation originating from the internal cored artery and we've looked at the posterior circulation originating from the vertebra basilis system and you can see that there's this communication between both circulations via the posterior communicating artery which which I've highlighted in green and this artery connects the internal cored to the posterior cerebral artery which I've outlined in yellow so that's the arterial Circle of Willis