The cerebellum lies below the cerebrum and develops from the hindbrain. It also consists of two symmetrical hemispheres, but these are much smaller than the cerebral hemispheres. The cerebellum is connected to the brainstem by three pairs of stalks, the pedunculi. These pedunculi are nerve tracts between the cerebral cortex, the spinal cord and the brain stem, and relay information from these parts to the cerebellum. The cerebellum acts like a very complex computer, which is responsible for the co-ordination of movement and posture. When an action is initiated the cerebellum, through its widespread connections, monitors the progress of movement and integrates the contractions of some muscles with the relaxation of others, thus ensuring a smooth completion of the action. It increases the excitability of some motor nerves and reduces it of others. Also the cerebellum is necessary for control of balance, because it integrates information about the posture of the body as a whole. Damage to the cerebellum causes ataxia and muscular tremors. A person with cerebellar damage can walk, because he can move all his muscles, but there is no co-ordination and his gait is wide and staggering, like someone who is drunk.