Hello anatomy colleagues this is Dr. Alsup and in this session we are going to focus on the
arteries we want to be able to identify in the cranial cavity and brain session. So we're going
to focus on an inferior view of the brain for this discussion because it really affords the
best view of these structures. So let's get started. I hope we remember that the brain is supplied by
two main arterial sources and the vertebral arteries which are a branch of the subclavian
artery are one of these. And so you can see the two vertebral arteries right here on this image
I'm going to outline both. And these vertebral arteries are closely associated with the medulla
oblongata. And it's not uncommon for the caliber or the size between the right and the left to
vary as we can see very clearly here on this donor that we have one that's quite a bit larger.
These vertebral arteries will traverse the foramen magnum and there is one branch of the vertebral
artery we want you to be able to identify which is the posterior inferior cerebellar arteries. And we
lovingly abbreviate this to pica sometimes you'll hear people say pika but I think pica is the way
to go. So you can see these coming off transversely but before the vertebral arteries coalesce
to form the basilar artery so it also has the pica also has a very close relationship to the
accessory nerve as it ascends from the spinal cord up through the foramen magnum. Okay let's focus on
the basilar artery now and this is formed by the coalescence of those vertebral arteries that we
saw in the previous image. And it is going to run down the midline of the pons. This artery
is named because of its close relationship with the cranial base so the basilar artery. And there
are three branches of the basilar artery that we want you to be able to identify. The most proximal
of these and the smallest is going to be the anterior inferior cerebellar artery so very close
in terms of name to the pica but we're adding an anterior so often you hear this abbreviated as ica.
And this is as mentioned typically smaller certainly smaller than the
pica. It will often form an anastomosis with the pica or the posterior inferior.
It's also closely associated with the abducens nerve which you can see right here.
Next we have the superior cerebellar artery which you can see nicely on this side and the posterior
cerebral artery. So right here is going to be the superior cerebellar and this will be the posterior
cerebral. And these are going to be the two kind of terminal branches. And before we move on from the
basilar I do want to point out that you do have a cranial nerve that I'm circling right there
which is cranial nerve III or the Oculomotor that is located between the superior cerebellar
and the posterior cerebral artery. So if you have some form of aneurysm or occlusion or something
that causes an increase in size of these arteries it could cause compression of the oculomotor nerve
which would have implications in terms of the movements of the extraocular eye muscles.
The other main arterial supplier to the brain is the internal carotid artery or the ica. This
artery and its branches will be a major supplier to the forebrain. And when you're looking at this
view of the brain the internal carotid artery had to be cut in order to remove the brain. So
what you will often see are these fairly large cut portions so fairly large in terms of caliber
for the internal carotid artery. And there are going to be two paired terminal branches of the ica. The
largest and what almost looks like a continuation of the ica are the middle cerebral arteries.
And so these are going to be as mentioned the largest. These will be located kind of
running towards and within the lateral fissure on the brain so it's often easiest to see the
middle cerebral when you have retracted the temporal lobes in order to better view these.
The smaller terminal branches which i'm outlining right now are the anterior cerebral arteries. And
these are going to be connected by this very small anterior communicating artery which I just drew
an arrow to so you can just see I'm outlining right there how small this artery actually is.
And then the anterior communicating arteries will continue more anteriorly as its name
would suggest and actually runs through the longitudinal cerebral fissure region.
You can see that it has this really close relationship
to the optic chiasm region so it's kind of running anterior to the optic chiasm.
The last branch of the internal carotid we want you to identify is another small
communicating or connecting artery which is the posterior communicating artery. So you can see
posterior communicating arteries coming off of the ica and this is will actually connect
to the posterior cerebral artery which recall was one of the terminal branches of the basilar
so this is where you're getting that connection between the ica and the vertebra basilar system.
And lastly I want to just walk through the cerebral arterial circle which we will most
typically hear referred to as the circle of willis. And this is composed of branches that
we've already discussed and identified but I just want to review these in the general area
as this is such a clinically important area. So the circle of willis is this prominent anastomosis
on the inferior portion of the brain of branches of the ica as well as the basilar artery. And
the circle will surround the infundibulum or pituitary stalk of the pituitary gland
as well as the optic chiasm which are going to be more medial to the circle of willis so you can see
it kind of surrounding that region. It is going to be composed of the anterior cerebral arteries
connected by the ever so small anterior communicating artery so that's where you're
getting communication from the different branches of the ica. And then posteriorly you
have that posterior communicating artery that is attaching or connecting the ica.
Sometimes it'll connect the middle cerebral but typically the more typical pattern is ica to
the posterior cerebral artery. And remember that posterior cerebral and it'll do so on both sides
that posterior cerebral artery is a terminal branch of the basilar so that is this posterior
communicating is how you're getting a connection between the ica and the vertebrobasilar system.
Excellent so I believe that is about as much fun as we can have with arteries of the brain.
It has been fun finally getting to see the internal carotid
artery have some branches unlike what we saw when we were dissecting the neck.
As always, if after you review and you find areas of confusion, please always feel free to contact me
or any of my anatomy colleagues with questions. Have a great rest of your day.