The brain is the body’s central control unit. This marvelous mass is the repository of emotions and memories; philosophers even have believed throughout history that the brain may house the soul. The nervous system’s main organ, the brain handles most of the body’s activities, processing information received from within as well as without. It is the seat of cognitive abilities and emotions, handling long- and short-term memory, thought, and the making of decisions.
Matters of Size
The size of the human brain varies widely, depending particularly on sex, age, and the overall mass of the body. Studies have suggested that the brain of an adult male weighs about 1,336 grams on average. The adult female brain, in contrast, weighs an average of about 1,198 grams. The human brain is far from the largest among the animals in terms of dimensions: the sperm whale has that distinction, but human brains contain the most neurons.
The brain has three parts: the brainstem, the elongated segment that connects the brain’s whole to the spinal cord; the cerebrum, the largest part of the brain responsible for conscious thought; and the cerebellum, located at the brain’s back, involved in regulating motor learning and movement. All of these parts are made of tissue that is soft, both white and gray matter. They contain high water content and a large percentage of fat.
Despite its moderate size compared to other organs, the human brain requires a great deal of energy to continue functioning. A human’s brain weighs only two percent of the mass of the body but uses a quarter of the energy the body needs to run each day. It seems to use up quite a bit of energy in its resting state, but even then, the brain seems to be assembling a map of information that is being accumulated.
There is a myth that humans only use a tenth of their brain capacities. Brain scans have disproven this thoroughly, however. They show that humans use all of their brains pretty much all the time. This holds true even in sleep. Even when a person is engaged in a task, the rest of the brain is busy doing other things.