Taking a look at our arteries that supply the cerebrum specifically, we’re going to take
a look here on this medial view the course of the anterior cerebral artery. So again,
this is going to travel on the medial side of the cerebral cortex as an anterior course passing
anterior to your corpus callosum and then circles back, if you will and winds back over
the corpus callosum. Then it will send some branches over the superior aspect of the
cerebral cortex that it supplies. The posterior cerebral artery is shown in through here
as a much more posterior course as you would imagine. You can see it branching.
You can see it supplying the more posterior aspects of the cerebrum. Now, I want you
to focus on each one of these arteries in a little greater detail. What we want to do is to
understand the actual distribution of first the anterior cerebral artery and then the posterior
cerebral artery. So, the area in blue on this lateral view represents the territories supplied
by the anterior cerebral artery. So those areas would include the medial, frontal,
and parietal lobes, so more on the medial side of this view. The anterior cerebral artery
also supplies the anterior limb of the internal capsule. It also will supply most of the
corpus callosum, the structure that connects the cerebral hemispheres to one another.
Here we see on the medial view in blue again, shaded in blue the distribution of the
anterior cerebral artery. All the medial side of the frontal lobe, all the medial side of the
parietal lobe essentially is being supplied here. Now, we want to take a look at the
middle cerebral artery and the territory that it supplies. That’s the area that’s shown in
through here. The territory supplied by your middle cerebral would be the lateral frontal,
lateral parietal lobes, as well as a portion of the temporal lobes. With respect to the
internal capsule, it’s going to supply the genu and its posterior limb. This is the vessel
that will give rise to branches that supply most of the structures that belong to the
basal ganglia. Posterior cerebral artery is next. We can see the distribution on the
lateral side is somewhat minimal, more so on the medial side. It will supply the occipital
lobe which we see here. It supplies this portion of the temporal lobe laterally. It’s also
responsible for the arterial supply to the midbrain which would be a structure outside
of the cerebrum or the cerebral cortex obviously. That would be a brainstem structure.
Arterial supply of the posterior cerebral artery here in the medial view, we can see it
supplying the occipital lobe. Then we see it supplying this area of the temporal lobe.
This particular image allows us to understand the arterial supply to the homunculus.
This is very useful for you clinically in establishing where a stroke may be. So if there’s
paralysis of the lower limb for example versus paralysis of the upper limb, this will
allow you to identify which artery is involved in producing these symptoms.
So if we take a look here, we have our famous homunculus. Here is the abdominal area,
thoracic area. We see the upper limb and a large area for the hand. Of course, our face
is out here and our larynx is here. Then on the medial side, we see the lower extremity
with the feet being the most inferiorly located here on the medial side of the precentral gyrus.
This area shaded in kind of the bluish color is going to be the supply to the homunculus
coming from the anterior cerebral artery. These areas here on either side shaded in the red
color are going to be the areas of the homunculus supplied by the middle cerebral artery.
So, let’s say for example that you have a patient who has paralysis of the lower extremity.
You’re trying to isolate which artery would be involved in producing that paralysis and
understanding the blood supply here to the lower limb. Within the precentral gyrus,
this is going to involve the anterior cerebral artery. Next, arterial supply to the internal
capsule, the internal capsule has an anterior limb that we see running within here.
It has a band called the genu right in through here. Then we see at that band the internal
capsule kind of changes its course and then has this orientation or direction. This is the
posterior limb. What’s important about the internal capsule is there is a somatotopic
organization with regards to the muscles that are being supplied through nerve fibers
traveling in the internal capsule. So, we can see here at the genu area, you’re looking at
muscles that are associated with the face and neck. Then as we proceed down the posterior
limb of the internal capsule, as we go in this direction, you’re moving down the direction
of this homunculus within the internal capsule. So that by the time you get here, you're looking
at the feet area. So if you think about a stroke and what is supplied by the cerebral
arteries here, the anterior cerebral artery supplies the anterior limb. So, a stroke there
would have no impact on muscle control. The genu in the posterior limbs, however
are supplied by the middle cerebral artery. So there is potential that if it’s involved
in a stroke that you could have a lesion within the internal capsule as a result.
Lastly, I want you to understand watershed territory. Watershed area is an area of the brain
that’s fed from two arterial sources. So, this could be between anterior cerebral artery,
middle cerebral artery for example or it could be between the middle cerebral,
posterior cerebral as well. These are just a couple of watershed possibilities. If we take
a look here again, this was an image that we used before to identify the territories
supplied by your anterior cerebral artery, that in blue and then the middle cerebral artery
is this area shown in through here. So, if you focus your attention here in the frontal lobe,
you will see this boundary between the anterior cerebral and the middle cerebral. So there’s
an overlap of those two blood vessels to this area of cortex. So, a watershed territory here
would be fed by the anterior cerebral and the middle cerebral arteries. You can have what
is known as a watershed infarct if the driving pressure to this watershed area is diminished.
Another example is that you certainly could have a watershed territory between the middle
cerebral artery and the posterior cerebral artery. Here is the territory supplied by your
posterior cerebral artery. Here is the territory supplied by the middle cerebral artery.
So this would be a watershed area, for example, here between the posterior cerebral
and the middle cerebral arteries.