The adult human brain weighs about 3 pounds (1300-1400 grams). By comparison, a sperm whale brain weighs about 7 pounds, a dolphin brain weighs about 4 pounds and a gorilla brain about 1 pound. (Jensen, 1998) Humans have large brains relative to body weight. Close to the size of a large grapefruit or cantaloupe, the brain is 78% water, 10% fat, and 8% protein. A living brain is so soft it can be cut with a butter knife. (Jensen, 1998)
A view of the outside of the brain shows convolutions, or folds. These folds are part of the cerebral cortex. The cerebral cortex is the orange-peel-like outer covering of the brain. The folds allow the covering to maximize surface area. In fact, if it were laid out, the cortex would be about the size of an unfolded single page from a daily newspaper. (Jensen, 1998)
The human brain is divided into cerebral hemispheres: the left and the right. The two sides are connected by bundles of nerve fibers, the largest known as the corpus callosum. The corpus callosum has about 250 million nerve fibers. (Jensen, 1998) The corpus callosum allows each side of the brain to exchange information.
Scientists divide the brain into four lobes: occipital, frontal, parietal, and temporal. The occipital lobe is in the middle-back of the brain. It's primary responsible for vision. The frontal lobe is the area around your forehead. It is involved with purposeful acts like judgment, creativity, problem solving, and planning. (Jensen, 1998) The temporal lobes (left and right side) are above and around the ears. This area is primarily responsible for hearing, memory, meaning, and language. (Jensen, 1998) However, there is some overlap in lobe functions.
The middle of the brain includes the hippocampus, thalamus, hypothalamus, and amygdala. This middle area is known as the limbic system. The limbic system is responsible for emotions, sleep, attention, body regulation, hormones, sexuality, smell, and production of most of the brain's chemicals. (Jensen, 1998) In the back-lower area of the brain is the cerebellum, which is primarily responsible for balance, posture, motor movement, and some areas of cognition. (Jensen, 1998)
(figures available in print form)