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Need-to-know anatomy
The brain is divided up into three main parts: the cerebrum, the cerebellum, and the brain stem. In humans, the cerebrum is the largest part of the brain and is responsible for most higher-level brain functions, including language, consciousness, emotions, integration of sensory stimuli, and some motor functions. The second-largest structure in the brain is the cerebellum. This portion of the brain governs balance and some other aspects of movement. Finally, the brain stem, the smallest part, is the most "primitive" part of the human brain and controls many of the body functions that occur automatically, including heartbeat, blood pressure, and wakefulness. Each part of the brain breaks down into smaller regions that control various body functions and behaviors.
A complex system of arteries, capillaries, and veins provides the brain with blood. Two vertebral arteries run alongside the brainstem and join at the basilar artery. The basilar artery then branches off to the cerebellum and the cerebrum. Branching off the heart, the aortic arch feeds another major pair of arteries, the left and right carotids. At the base of the brain, the vertebrobasilar arteries and the carotid arteries form a structure called the circle of Willis, which gives rise to many of the arteries serving the brain.
Since specific parts of the brain govern specific behaviors and bodily functions, doctors can usually estimate where the brain damage from a stroke occurred by examining the patient. For example, if a stroke victim can't move his or her left arm, a doctor might assume that the stroke damaged the section of the cerebral cortex governing motor function in the right hemisphere (the right side of the brain controls the left half of the body and vice versa).
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