Your brain helps you think, feel, learn and move. Your brain keeps your heart beating and your lungs breathing without you thinking about it. Your brain uses about 20 percent of your body's energy.

Your brain is inside your head. A hard skull protects it. Layers of tissue called the meninges lie between the brain and the skull. A grown-up's brain weighs about 3 pounds.

The biggest part of the brain, the cerebrum, has a left half and a right half. Each side of the cerebrum has four lobes. The occipital lobe is at the back of the brain. The temporal lobes are on the sides of your head, near your ears. The cerebellum is a small part at the back of the brain.

Your brain is made of billions of tiny cells called neurons. Nerve cells called neurons send messages all over your body. A neuron's branches, called dendrites, receive signals from other neurons. Neurons pass messages along using tiny electrical signals. Motor neurons carry messages from the brain to the body, telling muscles when to move.

On September 13, 1848, a railroad crew member named Phineas Gage was hurt when blasting rock sent an iron rod through his head. The iron rod that hit Phineas Gage was about 3 and a half feet (43 inches) long and weighed 13 pounds. Phineas Gage survived the accident, but he lost the sight in his left eye.

The hippocampus helps the brain form long-term memories. When you learn, your neurons form new connections. Experiences shape the brain, and they can keep shaping it even in adulthood.

Words to know

• meninges: tissue layers
• hippocampus: memory helper
• dendrites: receiving branches
• cerebellum: small rear part