The average adult brain weighs around 3 pounds, 75 percent of which is water and just 10 percent of which are neurons. The average newborn's brain weighs around 400 grams, and the brain needs 20 percent of the body's oxygen and 25 percent of the body's glucose even if it only makes up two percent of the total body weight.
The primary parts of the brain are the cerebrum, cerebellum and brain stem. The cerebrum is responsible for thinking, emotions, hormones, regulating body temperature and sleeping. The cerebellum controls balance, muscle activity and coordination, while the brain stem is responsible for unconscious functions such as the heartbeat, reflexes, breathing and digestion. The right hemisphere controls the left side of the body, while the left hemisphere controls the right side.
Blood vessels that stretch a combined length of roughly 200,000 miles feed the brain with oxygen. The brain can only go five minutes without oxygen before damage occurs, and a person loses consciousness just ten seconds after a loss of blood supply to the brain.
The human brain has 100 billion neurons and is made up of 60 percent fat. It is larger than the brains of most animals and generates enough current to power a light bulb. It is protected by 28 skull bones and is always working, even during sleep.