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  © 2008
  University of Idaho
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  Psychology Dept.
  University of Idaho
  Design - P&D  CTI

As we can see from De Armond, the first thing that happens when we’re talking about the circulatory system is that you’re going to get blood vessels from the heart.  The heart is going to send blood to the aorta, which is the major structure that comes off the heart.  From the aorta, it branches off into two major arteries (and other arteries as well), but for the brain and the structures that are important for us, there are two that are important.  First is the carotid and second the subclavian. 

The carotid artery, as we see in slide three, is basically the artery in the neck and under the jaw.  You can actually feel it if you put your fingers up underneath your jaw.  The carotid artery branches into the internal carotid artery, which then enters the cranium and goes up into the brain.  It’s going to transverse the sinuses and then branches off the ophthalmic artery. It then continues up into the system, penetrates the dura, and branches into the anterior and middle cerebral arteries.  Finally, it emerges from the sinuses and branches off the anterior carotid artery.

The anterior cerebral artery, as we see in slide four, basically supplies the cortex.  It also supplies white matter of the inferior frontal lobe and other structures as well.  In addition, it’s going to branch into smaller branches which will go to other locations.  It also is going to supply, as we see in slide five, the deep cerebrum.  It also supplies structures of the diencephalon, the limbic system, caudate and also the anterior limb of the internal capsule. 

The middle cerebral artery, on the other hand, supplies most of the cortex and white matter.  Its smaller branch also supplies very deep white matter and diencephalic structures including some of the internal capsule, the putamen, globus pallidus, and other structures.

The interior choroidal artery (shown in slide seven) supplies the anterior hippocampus and the posterior internal capsule.  These are the structures are supplied from vessels that are going to come off the carotid artery. 

What about the subclavian artery, what does it do?  Well the subclavian artery (as we see in slide eight) comes from the aorta and, or what is called the innominate artery.  Basically, it supplies the upper extremities of the arms.  Now, the subclavian artery is going to send off a branch called the vertebral artery, and the vertebral artery is really the artery that’s going to be important for the brain.  The vertebral artery is going to enter the cranium through the foramen magnum.  As it gets in there, it’s going to branch and give off what is called the anterior spinal artery and the posterior inferior cerebellar artery.  Ultimately these are going to rejoin again at the pons and medulla to form the basal artery.  The basal artery, as we see in slide nine, divides into posterior cerebral arteries, and it’s going to supply the inferior temporal lobe and the medial occipital lobe. 

Now there are many, many other arteries that I have not discussed here.  If you need to, or want more detail, you can go into a very good anatomy book.  But in general, these are the major ones that we talk about when we discuss supplying blood to the brain and specific structures.

Now there’s one final set of structures that I want to discuss that is located at the very base of the brain.  This is what you see primarily in figure 99.  These collection of structures are called the Circle of Willis.  The Circle of Willis is basically a collection of major vessels that all connect together.  They’re located again at the bottom of the cerebral cavity and they generally loop around the brain stem.  The Circle of Willis, (because there are so many blood vessels here) is a very nice place where tumors begin.  It’s also a very inexcessable location to get at.   Since you have many, many major arteries located there it becomes an extremely difficult place to do surgery and other things.

There are a variety of different structures in the Circle of Willis.  These include structures from the anterior communicating artery, internal carotid, interior cerebral arteries and others.  All of these structures are shown on slide 11.

There’s a major loop though within this system.  The two anterior cerebral arteries are connected by the anterior communicating artery, and the two posterior cerebral arteries are connected to the internal carotid by the posterior communicating arteries.  So, what you have is a loop of structures that are going to go around and form a circle.  All of these innerconnections, when you put them all together, are what we call an anastomoses.  Anastomoses (slide 13) are inner-connections between blood vessels.  They protect the brain and other structures when blood supplies are blocked.  The classic example is within the Circle of Willis, so as we can see if you blocked one structure, say one of the major parts, the blood supply would still go to the brain because it would go around the loop.  It would be a little slower to get there and you might show some particular symptoms with some exertion, but in essence you would still be getting blood supply to the brain and the brain tissue would not die. 

So, we’ve talked now about a variety of different structures that are within the brain, let’s talk about some particular problems that occur from vascular disorders.  These are what we call cerebral vascular accidents or what you commonly call strokes.  There are two major types of strokes (shown on slide 15).  There are occlusive strokes and what are also called hemorrhagic strokes.  In general, all strokes are basically due to problems within some blood vessels.

Let’s talk about occlusive strokes first and shown in slide 16.  Basically in an occlusive stroke, there’s a blockage (usually due to arteriosclerosis.  So make sure you have high levels of good cholesterol and low levels of bad cholesterol).  In essence, the blood flow is obstructed. As a result of that, you get insufficient blood supply to the tissue (ischemia).  If you don’t get much blood you start having weaknesses.  If you get complete blockage, that is there is no blood supply to the tissue, the tissue ultimately dies.

Now occlusive strokes are much different from the other type of strokes (shown in slide 17).  These are called hemorrhagic strokes.  Hemorrhagic strokes occur because of some kind of rupture or damage to a vein or artery.  What will happen is that blood flows from these structures and because it’s acidic, it destroys the membranes of somas and kills neurons.  Now, we all have some strokes.   We all have some minor ruptures due to trauma and other things.  But, if you have a good clotting mechanism, the damage we usually have is minimal or doesn’t occur at all.  However, if you damage a major artery, such as the middle cerebral artery or some other structures within an occlusive or a hemorrhagic stroke, it becomes a very serious problem.

Now the brain damage that one gets from a cerebral vascular accident depends on which structure is blocked or ruptured, and it’s also going to depend upon the duration of the blockage or the rupture.  Thus, if you just have a little rupture and it’s blocked relatively quickly, you’re not going to have many symptoms. On the other hand, if you block something for a long period of time and you get major destruction of tissue, then you’ll have major, major problems.  Ultimately as we see in slide 18, the symptoms are related to the vessels that are impacted.  So the symptoms are going to depend upon which blood vessel is blocked or damaged. 

Now let’s talk about one of these structures in detail for a couple seconds.  This is one that most usually causes disorders (Seen slide 19) and is called the middle cerebral artery.  This is the artery where you commonly get major disorders that occur and it’s the most frequent.  The symptoms are basically collateral weakness.  So, if you have damage on the left side of your brain, you’re going to have collateral weakness and symptoms on the right side. You’re also going to get sensory loss, and visual problems depending on the side of brain you’re damaging, you may have language problems as well.

The damage, (as we see in slide 20), affects the arms and the face.  It is basically due to the location where the damage is occurring.  Usually where you have the greatest deficits, damage, and symptoms is in the motor and sensory areas in the hands.  Again, if you have damage on the left side of the brain, you’re going to get a facial or language problems as well.

Now, there are many, strokes that occur in other different arteries.  You can look at a variety of anatomical texts to get an idea of what particular symptoms might show.  But in general, most cerebral vascular accidents share a common set of symptoms and so let’s talk about these a little bit on slide 21.

Generally what you commonly see are two different types of symptoms.  The first type of symptom is a sudden weakness or numbness in a body structure.  That is, you can’t move your arm anymore, or you can’t stand up anymore because one side of your body doesn’t have muscular control.  Or you don’t feel anything, so your hand becomes numb, etc.  However, the same symptoms may also occur over time and they may be gradual.  Oftentimes we mistake these particular types of symptoms for problems associated with old age.  Similar symptoms such as coordination problems, memory and confusion problems, pupils being unequal or basically not constricting together, etc. are other symptoms that you commonly see with cerebral vascular accidents.

 Again, the loss of memory, loss of coordination and confusion oftentimes are associated with old age.  Many times these are not in fact old age problems, but due to some kind of obstruction within a blood vessel.  Of course, the person may be conscious or unconscious while all of this is going on.  So what do you do if you think that you have a stroke, you’re having a stroke, or you suspect someone is having a stroke?  Well, as we can see in slide 22, if you’re having gradual weakness or symptoms or other kinds of problems, the thing you should do is make an appointment to see your physician AND DON’T PUT IT OFF.  Get in there and do it right away.  If you’re having major symptoms, immediately, keep the person from moving around, and get a paramedic team or ambulance there immediately.  Basically, what you need to do is get the person to a hospital very, very rapidly.  Depending upon the type of stroke, (e.g., if it’s an occlusive type of stroke), there’s a variety of different drugs that one can give to break down those occlusions and blockages that we have within the brain.  As a result, oftentimes the damage that one experiences is relatively minor.  There’s also a variety of other drugs that we use in hemorrhagic strokes.  The problem with hemorrhagic strokes is that the damage is oftentimes extensive.  Consequently, the person may remain in a coma and die depending on the size of the blood vessel that’s been ruptured.

In general if you want to have damage to your brain, you want to have an occlusive stroke because you only have one particular area that’s been damaged.  If you have a hemorrhagic stroke, the blood goes everywhere across the system, and where it goes it kills things.

In general, this section has reviewed a variety of aspects related to cerebral vascular accidents.  In our next sections, we continue on with our discussion of particular disorders that we have within the nervous system and the brain.  So until then, we hope you’re having yourself a great day.