hello all this is dr. Alsup and we are talking blood supply to the brain a very important area
for sure so there are two main arteries that will supply the brain in each one of these
arteries will have multiple branches and we'll talk about each one and kind of where we will
locate them and some of these branches will make up what is referred to as the cerebral arterial
circle but you'll more likely hear it referred to as the Circle of Willis and we will discuss
why this is important in terms of maintaining constant blood supply to the brain so let's get
started all right there are two pairs of arteries that supply blood to the brain these will be the
internal carotid artery which you can see here and the vertebral arteries which you can see here the
internal carotid artery is a terminal branch of the common carotid artery recall that the
internal carotid artery was the branch that had no branches in the neck like the other terminal
branch the external carotid artery so now it is the internal carotid arteries time to shine and
it will enter the skull via the carotid canal the vertebral arteries are branches of the first part
of this subclavian typically it's the very first branch of the subclavian and this artery will
ace in the transverse foramina of c6 through c1 and then it will enter the skull via the foramen
magnum as you can see the framing magnum right here it is the two vertebral arteries that will
unite to form the basilar artery which you can see here but before we get to the basilar artery let's
talk about some of the branches of the vertebral artery after it is a sended through the foramen
magnum but before they unite to form the basilar so the first one we're going to discuss is the
anterior spinal arteries which you can see here and here and they will come together - they will
unite in this region and run down the midline of the medulla and will descend to supply the anterior
portions of the spinal cord thus its name so you will have the one anterior spinal artery
after you have contributions from both of the vertebral arteries typically the largest branch
of the vertebral arteries will be the posterior inferior cerebellar cerebellar artery excuse me
which many anonymous lovingly referred to as PICA. PICA will supply parts of the cerebellum
and the medulla and will typically give off its own branch the posterior spinal arteries and so
the posterior spinal arteries are the posterior counterparts of the anterior spinal artery so it
will run on the posterior side and at around the junction of the medulla and the pons you can kind
of see if this is pons right here and this is medulla here you can see about where those two
vertebral arteries are coming together to form the basilar artery and as you can see the base lower
artery is an unpaired artery many of the orders we're discussing are paired there's a right in
the left but the basilar artery is unpaired it is named for the bait the the basilar artery excuse
me is named due to its close relationship with the cranial base and as you can see it is running
down the midline of the ponds or if it was near the surrounding bone if we were looking at the
surrounding bone it would be on that basal or part of the occipital bone or the clivus so very near
the junction of where the vertebral arteries turn into the basilar artery you typically have the
first branch of the baler which is the anterior inferior cerebellar artery or the icon the basilar
artery also gives off many smaller branches in this region none of which you have to learn their
names but we are going to share our identification and understanding for the two terminal branches of
the basilar and these are going to be the superior cerebellar and the posterior cerebral and note
here that we do have to differ talking's cerebral ear and cerebellar here and it makes sense we're
looking at the posterior portion of the cerebrum and the anterior portions of the cerebellum so
that's why we have that those different names here in terms of what they're supplying but sometimes
it gets difficult to say these because these two names are so close together now one thing
I want typically that posterior cerebral artery is going to be the larger of the two terminal
branches one thing I want to note here is that between these two arteries you're going to see
a little bit of a nerve you can see it nicely right here that's going to be located between
the superior cerebellar and the posterior cerebral and that is the oculomotor nerve
or cranial nerve three so think about it if you have clotting or over dilation of one of these
arteries that can really compromise the oculomotor nerve which efferent lee serves four of the six
extraocular eye muscles and it also transmits pre ganglionic parasympathetics destined for the eye
so that kind of implications in terms of the the target organs for the oculomotor nerve all
right moving to the opposite in let's talk about the internal carotid artery and one thing that I
actually didn't label in this image is the actual internal carotid artery it has been cut in this
dissection but this small portion right here is the internal carotid artery you can see how large
it actually is in terms of diameter compared to some of the other arteries in the region let me
actually start with one of the branches of the internal carotid artery that we actually can't
see in this image and it's something that we're going to spend quite a bit more time on in the
orbit and cavernous sinus session and that is the ophthalmic artery ophthalmic arteries this
is going to be the main arterial supply to the eye in the orbital region and it's not a focus in this
image because we are focused mainly on those areas near the Circle of Willis or having to do with the
Circle of Willis okay let's start let's talk about the small posterior communicating artery
what you can see here and here on this image and that posterior communicating artery is what will
connect or allow anastomosis between the posterior cerebral artery and the internal carotid directly
or sometimes the middle cerebral artery so in essence the posterior communicating artery is
what's connecting the internal carotid artery to the vertebral artery so allowing blood flow from
those two different sources if need be the middle cerebral artery is going to be located here and
here and it looks like almost a continuation of the internal carotid artery so fairly large in
terms of diameter as well the anterior cerebral artery you can see in two places you can see here
as one of the terminal branches of the internal carotid and you can see it extending anteriorly
here so if you retract portions of the frontal lobe you can see it continuing to supply the
frontal lobe in these regions so here on this side is the anterior cerebral and extending up
into this region now between these two anterior cerebral arteries you can see this itty-bitty
arteriole branch that is connecting the right and left anterior cerebral arteries and that is the
anterior communicating the anterior communicating artery is unpaired which is unlike what you saw
with the posterior communicating artery switch you do have a right and a left posterior communicating
artery alright so let's take our knowledge of these branches and make the cerebral arterial
circuit circle or the Circle of Willis the this area is important in terms of an Eskimo
these around the brain or base of the brain so what do I mean by an estimation all I really
mean here is communication it's going to provide detours for blood flow in case the usual pathway
is obstructed by say compression due to position of a joint pathology that's occurring in a certain
artery or surgical ligation so having to tie off an artery so this will allow for other portions
of the brain to have blood supply if a certain artery is occluded or something is occurring there
so very important there the basilar artery and the internal carotid arteries have branches that will
communicate with one another and they'll allow for this flow of blood to continue if any issues
occur so let's review the Circle of Willis from anterior to posterior you're going to have that
anterior communicating artery that is going to connect the anterior cerebral arteries which I
am labeling here so I'm just going from anterior to posterior these numbers don't really mean all
that much other than just kind of showing you the flow so there you have that small anterior
communicating artery connecting the two anterior cerebral arteries so allowing blood flow between
branches of the right and left internal carotid arteries the internal carotid arteries are going
to be connect so you're going to have the internal carotid arteries here so these are internal
carotid here and here and these are going to be connected to the to the branches of the basilar
artery of via the posterior communicating here in here so you can say that those internal carotid
arteries are a portion of the Circle of Willis then you will have those posterior communicating
artery connecting the posterior cerebral arteries alright so the things that I have
numbered here are going to be components of the Circle of Willis so anterior communicate artery's
anterior cerebral the internal carotid sometimes the middle sometimes the middle cerebral but we're
going to go with internal carotid for our purposes the post posterior communicating and then lastly
the posterior cerebral artery so this one is kind of the oddball because the rest are going
to be branches of the internal carotid whereas the posterior cerebral artery is a branch of the basal
er which is a branch of the vertebral artery so that's where you're getting that different
subclavian artery source rather than the internal carotid it is important to note that it may not
look like this perfect Circle of Willis in all individuals some people do not have all of these
anastomosis occasionally they have more enesta most people may be missing a communicating branch
so think through what some of the implications of lacking and an anastomotic branch could be and we
will discuss some of this in a bit more detail in an upcoming learning objective lecture but
think about what would happen say if you didn't have a posterior communicating artery on one
side what could happen now nothing could happen if there's no occlusion but say that there is
what are the implications there all right so those are the arteries around the base of the brain and
let's take a moment to review one of the concepts covered in this session so question the posterior
communicating artery allows anastomosis between the internal carotid artery and which other artery
is it a anterior cerebral artery the anterior inferior cerebellar artery or aikka see the
ophthalmic arteries D posterior cerebral artery or a superior cerebellar artery all right try to
answer this question without reviewing your notes kind of see where you are at with your knowledge
here and hopefully you have landed on that D or the posterior cerebral artery is the correct
answer so yeah here that posterior communicating artery allows communication between the posterior
cerebral artery and the internal carotid artery are occasionally through the middle cerebral
artery so it's that posterior cerebral artery that is the correct answer anterior cerebral artery is not
correct because it's associated with the anterior portions of the cerebral arterial circle so not
directly connected to the basilar artery the anterior inferior cerebellar artery is a branch
of the basilar artery but not typically associated with the Circle of Willis the ophthalmic artery
is incorrect as well it is a branch of the internal carotid artery and it will supply
the eye and the orbit region but not involved with the anastomosis of the base of the brain
typically and lastly and probably the trickiest of the distractors is the superior cerebellar
artery which is a terminal branch of the basilar artery similar to the posterior cerebral but it
is not typically the one that is connected to the posterior communicating artery all right I
hope you are beginning to feel more comfortable in this area as you review and have questions please
feel free to reach out with any questions and thank you for your time and attention