Brain Blood Supply: Internal Carotid & Vertebral-Basilar Arteries Explained

okay we're going to talk about blood supply to the brain and answer the questions what parts of the brain are

supplied by the internal carotid and vertebral basal or arteries and what is the Circle of Willis hello everyone my

name is dr. Morton and I am the noted anatomist so here are the different arteries that supply the brain that

we're going to talk about and I want to just focus for a second on the internal carotid and vertebral basilar artery so

the brain is applied by two arteries internal carotid and the vertebral basilar artery so in this lateral view

we're going to pull the brain out and take a look at a line that goes that vertical a kind of obliquely through the

temporal lobe and the top of the occipital lobe like that and so that the internal carotid artery right here

supplies the anterior circulation of the brain or in other words everything above that dashed line and the vertebral

basilar artery this artery right here these two vertebral arteries ascend up and then once they hit the frame and

magnum they join to become the basilar artery and they supply the posterior circulation of the brain so it looks

something like this this is the scaffolding in which all the other arteries are going to be shelved

into to show how that we supply the brain with blood so let's start with the internal carotid artery and its branches

first okay so the internal carotid artery which is right there in that dashed line okay

and in this lateral view the common carotid artery bifurcates into an external and internal carotid artery the

internal carotid artery ascends up and then goes through the base of the skull and so there's that base of the skull

where the carotid canal is and so if we zoom in there's our internal carotid artery and the carotid canal and both on

the bottom and in the cranial base and there's the carotid canal in which the internal carotid artery traverses so we

noticed that there's a part of the internal carotid artery in the neck cervical region in the carotid canal the

petrous region in the cavernous sinus and then that's supply in the brain so there's basically these four parts of

the internal carotid artery let's do it again the cervical part of the internal

carotid artery is in the neck what's shown there that's highlighted the cervical region then there's the petrous

part which is going from the carotid canal on the base of the skulls of the crowded canal in the middle cranial

fossa between the two is the internal carotid artery the petrous part then the cavernous part is the part that's in the

cavernous sinus so there's a sphenoid bone in a coronal section in blue is the cavernous sinus one of the dural venous

sinuses flanking either side of the pituitary and there's the internal carotid artery the cavernous portion the

only Prime in anywhere in the body where you see an artery inside of a vein it's very cool so let's take a look at this

angiogram where you inject a dye into the internal carotid artery and then take an x-ray of it where if we zoom in

and take a coronal section through this lateral view of the internal carotid artery there is the internal carotid

artery in the cavernous sinus but watch it goes boom and it curves around and then if we take another cross-section

there is the cerebral part of the internal carotid artery and basically the cerebral part is that part right

there where all the other branches that we're going to talk about come off the area is the internal carotid artery the

cerebral part and one of the major one of the branches that comes off is called the ophthalmic artery and as its name

implies goes to the eye so there is a superior view of the orbit our internal carotid artery there's the ophthalmic

artery going in through the optic canal and gives rise to all these arteries that go into the orbit and clinically a

really important one is the central artery of the retina that supplies arterial supply to the retina and if

it's occluded because of diabetes or a clot then blindness or vision problems occur

another artery that comes off the internal carotid is called the posterior communicating artery that connects the

posterior cerebral artery and the internal carotid arteries it also connects our anterior and posterior

circulations on one side there's our anterior circulation of the brain and there's the posterior circulation of the

brain and the posterior communicating artery x' connect the two together it's they're paired one on either side then

there's the anterior cerebral artery right there that that supplies the front of the

cerebrum so here's the front of the cerebrum and there's our internal carotid and there is one into your

cerebral artery coursing over top of the corpus callosum within the longitudinal cerebral fissure and that's paired the

intracerebral arteries they're paired okay the distribution of the anterior cerebral artery is the medial aspect of

the cerebral Hemisphere all the way back to the parietal lobe let's see what that looks like okay I'm gonna make the

anterior cerebral artery to look yellow because that's that the picture I'm gonna show is in yellow so here's a Sam

it'd sagittal section of the brain there's our internal carotid and there's our anterior cerebral artery and there

is the anterior cerebral artery coursing over the corpus callosum and you can see its distribution okay right in the

midline of the brain and so here's a midsagittal section of the brain and everything you see in yellow is supplied

by the anterior cerebral artery the medial aspect of the cerebral Hemisphere all the way back to the parietal lobe

and even in this lateral view of the right side of the brain there you can see the anterior cerebral artery is

supplying the medial aspect of the cerebral hemispheres back to the prata lobe all right now the anterior

communicating artery is between our two anterior cerebral arteries right there our anterior communicating artery let's

do that again from this and to your view there are showing our anterior cerebral arteries and she whoops and she right

there is our anterior communicating artery connecting the two together now our middle cerebral artery is right

there in middle cerebral because it's the middle of the cerebrum so here's the brain in anterior view there's our

internal carotid artery and there is our middle cerebral artery right within that lateral sulcus and so the distribution

is through the lateral aspect of the cerebral hemispheres except for the superior portion of the frontal and

parietal lobes and for the inferior part of the temporal lobe let's see what that means okay so here's a lateral view of

the brain there's our middle cerebral artery and there's its distribution and so if we look at this picture again

there's that everything in pink is showing the distribution supplied by the middle cerebral artery all

except the superior portion of the frontal and parietal lobes and in the inferior portion of the temporal lobes

and you can see the anterior cerebral and posterior cerebral arteries supply those two areas okay so now let's focus

on there's our internal carotid artery now let's go to the vertebral basilar arteries and they're consisting of the

vertebral and the basal or arteries so now let's take a look at the vertebral arteries and its branches so the

vertebral artery is located there it's paired one on either side and it arises from the subclavian artery and ascends

up the neck through the transverse foramina of the cervical vertebra through the frame and magnum and into

the skull and so there is the vertebral artery there's the base of the skull the occipital bone there in dot-dash line

I've added the frame in Magnum and the vertebral artery comes up traverses the frame in Magnum fuses with the other

vertebral artery and then become the basilar artery a branch of the vert blar tree is the PI Co the posterior inferior

cerebellar artery which is I've just drawn on there so let's take a look at this lateral view and there is our

cerebellum and there's the posterior inferior cerebellar artery and there's the territory supplied the bottom back

of the cerebellum we also have the anterior spinal artery when we take our two vertebral arteries and we add the

anterior artery there it then courses in front of the spinal cord there's our two vertebral arteries and there's our

anterior spinal artery it supplies the front of the spinal cord now let's go to the basilar artery and its branches and

so the basilar artery is a basically taking our two vertebral arteries and they come together to make the basilar

artery so here again is our two vertebral arteries and they come together to make the basilar artery the

courses all along vertically along the pons between the ponds and the clivus of the skull branches that come off include

the anterior inferior cerebellar artery there or the I Iike and there we have the cerebellum and there's the anterior

inferior cerebellar artery the supplies the front and bottom of the cerebellum we also have the superior cerebellar

artery that's more rostral II located and there is our cerebellum and there's our superior cerebellar

artery that supplies the top of the cerebellum and there we have the superior cerebral

cerebellar arteries also shown in this view then the very end of the basilar artery is showing the posterior cerebral

artery and the posterior cerebral artery is right there and it supplies the back of the cerebrum now I just want to take

a little tangent for a second you see there's the posterior cerebral artery and there's a superior cerebellar artery

Shing cranial nerve three exits between the two of them so if there's ever a berry aneurysm on the posterior cerebral

or superior cerebellar artery you can push on that cranial nerve three and have eye deficits alright so the

posterior cerebellar arteries distribution is through the occipital lobe our primary visual cortex and to

the temporal lobe the posterior median portion and the inferior portion so here's a midsagittal section of the

brain there's our basal ER and posterior cerebral artery and there is the distribution of the posterior cerebral

artery in this picture of the mid sagittal view the posterior cerebral artery in blue supplies the occipital

lobe and then that post your medial surface of the temporal lobe and in the lateral view you can see the poster

cerebral artery in blue supplying the occipital lobe and also the bottom or inferior portion of the temporal lobe so

now we've done the basilar artery let's talk about the Circle of Willis so what's the Circle of Willis well it's

collateral circulation between our two internal carotid arteries and the vertebral basilar artery so here we have

that same picture our two internal carotid x' and the basilar arteries and then it's the collateral connection

formed between those and are communicating arteries that's the Circle of Willis and it's named after this

anatomist named Thomas Willis he's from the 1600s is he named the Circle of Willis he also was one who numbered our

cranial nerves one through 12 we still do it he actually also was the one who put the word mellitus and diabetes

mellitus because he said hey that smells like honey let's call it the diabetes a lot of urination that smells like honey

okay Circle of Willis provides redundancy it permit circulation should a part of the circle be occluded what do

we mean by that well here's that picture again you can the Circle of Willis in that dashed area

now let's say that right there is an occlusion of the anterior cerebral artery within the Circle of Willis so

blood comes up through the internal carotid artery and she blocked so blood on this side cannot get through to the

anterior cerebral artery because it's blocked but now watch that blood comes in from the contralateral internal

carotid artery and then that blood can not only go to the anterior cerebral artery on its side but also go across

the anterior communicating artery and go up to the other side of the cerebrum and so this Circle of Willis provides

redundancy within the circle now if you go outside the circle these terminal branches become and artery so if you

block them that's how you get a scheme extra' but if you block within the Circle of Willis you can get this

redundancy pretty cool right and the Circle of Willis is formed around the optic chiasm and pituitary gland so

there is a Circle of Willis in red and then in yellow is the optic chiasm which is the cross form by our two optic

nerves and there's the pituitary gland infundibular stalk as well the Circle of Willis is around them and so if we look

at this lateral view that dotted line everything above it is provided by the internal carotid artery and its branches

everything below it is supplied by the vertebral basilar artery and its branches and there are all those

branches and that my friends is the blood supply to the brain in a nutshell [Music]

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