FIGURE 2.1. The brain owes its outer appearance of a walnut to the wrinkled and deeply folded cerebral cortex, which handles the innumerable signals responsible for perception and movement and also for mental processes. Below the surface of the cortex are packed a number of other specialized structures: the thalamus, an important relay station for the senses, and the hypothalamus, a meeting point between the nervous system and the endocrine system and between emotion and physical feeling. The pituitary gland, acting on signals from the hypothalamus, produces hormones that regulate many functions from growth to reproduction. The pons and the medulla, two major elements of the brainstem, channel nerve signals between the brain and other parts of the body, controlling vital functions such as breathing and deliberate movement. (The extension of this signal pathway throughout the trunk and abdomen is, of course, the spinal cord.) At the back of the brain is the cerebellum, which coordinates the brain's instructions for skilled repetitive movements and for maintaining posture and balance. Source: Adapted from G. J. Torbra, Principles of Human Anatomy, 3rd ed. Harper and Row (1983).