| Vessels
which supply blood to the brain. There are four blood vessels
supplying the brain, two carotid arteries and two vertebral arteries.
These vessels break up into other arteries within the brain.
The internal carotid artery enters the skull, passes through the cavernous
sinus, and then gives off the ophthalmic artery which supplies the
eye. Then it gives off the posterior communicating artery, the
anterior choroidal artery, and then it divides into the middle cerebral
artery and the anterior cerebral artery. The middle cerebral
artery supplies the motor portion of the brain, which controls movement
of the other side of the body, particularly the upper extremity and
face. The anterior cerebral artery gives off the recurrent artery
of Heubner, and the anterior communicating artery, which sends blood
to the other anterior cerebral artery on the other side of the brain.
The vertebral arteries run up along
the skull base, and merge to form the basilar artery, which supplies
the brainstem and then gives off the posterior cerebral arteries.
The arteries supplying the brainstem are the posterior inferior
cerebellar artery, the anteior inferior cerebellar artery, and the
superior cerebellar artery. The posterior cerebral arteries
give off the posterior communicating arteries, and then the medial
and lateral posterior choroidal arteries.
The vessels at the base of the brain
form a protective circle. If one of the arteries feeding the
circle is occluded, theoretically, the other vessels, if they are
patent, can take its place. The arteries involved in the circle
of Willis are, for example, the left posterior communicating
artery, left internal carotid artery, left anterior cerebral artery,
anterior communicating artery, right anterior cerebral artery, right
internal carotid artery, right posterior communicating artery, right
posterior cerebral artery, left posterior cerebral artery, and then
back to the left posterior communicating artery.
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Glossary 
