The human brain uses a large share of the body's energy even while you rest.

The longer version

Neurons are expensive cells to run. Every moment, millions of them pump charged particles across their membranes to keep a tiny voltage difference ready, and that maintenance work continues whether you are solving a problem or lying still. When a signal fires, the pumps have to restore the balance again, so activity adds cost on top of the baseline. Supporting cells, which insulate and supply the neurons, consume energy too.

The brain has almost no way to store fuel, so it draws a steady supply of glucose and oxygen from the blood. In many cases the share of total energy used by the brain is far larger than its share of body weight.

Where this entry sits

These facts look at how the human body works in ordinary moments, from breathing and blinking to balance and sleep. They focus on anatomy, senses, and small reactions that happen constantly without any conscious effort. The full list sits on the Human Body page, where every entry is listed in order.