An intricate system of arteries supplies the brain with the oxygen that it needs to function. The internal carotids and the vertebral arteries are the main vessels of the brain that supply blood to the brain. These arteries form a circle known as Willis' circle, which is named after Thomas Willis, the British physician who discovered it. Willis' circle is located at the base of the brain, where it is joined by other vessels of the brain. This arterial system is designed so that if there is a blockage in one artery, the blood flow can be diverted to other arteries.
The internal carotid arteries provide blood to the front of the brain. The left internal carotid provides blood to the left portion of the brain, and the right internal carotid provides blood to the right portion. As each internal carotid artery enters the skull, it divides into three branches that connect to the anterior cerebral artery, middle cerebral artery and posterior communicating artery.
The anterior cerebral artery provides blood to the frontal lobes. The frontal lobes are the parts of the brain that control personality, logical thinking and voluntary movement. The middle cerebral artery supplies blood to parts of the frontal, parietal and temporal lobes of the brain. This vascular territory is associated with the sensory and motor activities of the hand, arm, throat and face, and it affects speech.
The posterior communicating artery supplies blood to the temporal and occipital lobes. The temporal lobe controls memory, language and auditory processing. The occipital lobe controls vision and is responsible for tasks such as motor perception, spatial processing and color discrimination.
The vertebral arteries connect to the basilar arteries. These vessels of the brain supply blood to the brain stem, the rear of the cerebrum and part of the cerebellum. The brain stem coordinates movements on the left and right sides of the body. The cerebrum is associated with judgment, perception, decision making, thought and imagination, and the cerebellum controls balance and movement.
The brain requires a constant flow of blood to keep its tissues healthy and to support nerve function. It has been estimated that the brain uses approximately 25 percent of the oxygen in the body and almost 20 percent of the blood. Unlike other body tissues, the brain cannot store fuel, so it needs the continuous supply of glucose that constant blood circulation can provide. The vessels of the brain circulate blood throughout the brain to ensure that all of its nerves and cells receive the nutrients they need.