Learning is often treated as though it happens exclusively inside the skull. Conveniently for textbook diagrams, the body is usually reduced to little more than a transport system for the brain. Biology, however, is rather less tidy. While the brain contains around 85 billion neurons, hundreds of millions more form networks throughout the rest of the body, particularly in the spinal cord and digestive system. Likewise, many of the chemical messengers associated with attention, mood, and cognition are produced both inside and outside the brain, although they do not all perform the same roles or communicate directly across the brain–body divide. Movement, meanwhile, increases blood flow, helping deliver the oxygen and nutrients on which the brain depends. Energy breaks build on these connections, using a few minutes of physical activity to refresh attention before asking the brain to tackle the next intellectual hurdle.