In Depth: Inner Brain 2
The arteries of the internal carotid system supply most of the cerebrum, the part of the brain that houses the higher functions. The only parts of the cerebrum not supplied by these arteries are on the back and sides in the occipital and the temporal lobes, respectively.
The vertebral-basilar system starts as two vertebral arteries along either side of the spine, and these then join together as the basilar artery.
This artery feeds the parts of the cerebrum not handled by the internal carotid arteries. It also sends blood to the cerebellum and the brain stem, which lie at the base of the brain. The cerebellum is largely responsible for making the body’s movements more precise, and the different parts of the brain stem control much of the body’s involuntary functions. Blood from this system also supplies sections of the spinal cord.
Both systems provide blood to the diencephalon: its parts either route information from the rest of the body to the appropriate areas of the brain or control involuntary functions.
The main arteries of the internal carotid and the vertebral-basilar systems each have many smaller branches that funnel blood to more specific areas within the brain.
The two systems meet in what is called the circle of Willis, which also connects to the posterior and anterior communicating arteries.
There are also two systems of veins that take blood away from the brain. Superficial veins handle the outer areas, and deep veins take care of the interior.
There is also a set of internal cerebral veins. This pair merges into the great cerebral vein, which are also joined by the deep veins in the brain.
All of these veins drain into large venous passages called sinuses. Blood from the superficial veins flows into the superior sagittal sinus, and the deep and interior cerebral veins drain into the straight sinus.
These two sinuses join in what is called the confluence of the sinuses. From there, blood flows into the transverse sinuses and then the sigmoid sinuses before finally reaching the jugular veins. The blood then travels to the heart, where it is re-circulated to the major veins so it can receive fresh oxygen.