The Human Brain Weighs About Three Pounds

For something that does so much, the brain does not weigh a great deal. The National Institute of Neurological Disorders and Stroke, part of the US National Institutes of Health, describes the brain as a three-pound organ and as the most complex part of the human body. The institute sums up its work in a single sentence. The brain is the seat of intelligence, the interpreter of the senses, the initiator of body movement and the controller of behavior. That covers thinking, seeing and hearing, moving, and how a person acts. The institute also describes where the brain sits: lying in its bony shell and washed by protective fluid. It calls the brain the source of all the qualities that define our humanity.