Human brain sectioned to reveal the outer and inner structures. Regions of the outer brain, the cerebrum and cerebellum are depicted. The cerebrum, the largest part of the brain, presents a complexly convoluted surface characterized by sulci (grooves) and gyri (fissures) which outline specific functional areas. The wrinkled cerebellum, below the cerebrum, facilitates smooth, precise movements and controls balance and posture. The inner brain structures include the thalamus, which acts as the brain's information relay station; the limbic system, involved in stress reactions; the hypothalamus, which controls the automatic processes of the body; and the brain stem, which acts to regulate essential functions of the body including blood pressure, heartbeat, digestion and respiration.