Nervous System

The nervous system is the body's control and communication network. It is made up of the brain, the spinal cord, and a huge web of nerves that reach every part of the body. The nervous system tells your heart to beat, your lungs to breathe, and your hand to pull back from something hot. It also lets you think, remember, feel, and dream.

The system has two main parts. The first is the central nervous system, which is the brain and the spinal cord. The second is the peripheral nervous system, which is all the nerves that branch out from the spinal cord to the rest of your body. Together, these two parts work like a phone network. The brain is the headquarters, and the nerves are the wires that carry messages back and forth.

The messages travel along special cells called neurons. The human body has about 86 billion neurons, and most of them live in the brain. Each neuron is shaped a bit like a tiny tree, with branches that pass signals to other neurons. The signals are partly electric and partly chemical. They can race through your body at up to 268 miles per hour, faster than a race car.

Some of what your nervous system does, you choose. Picking up a pencil, kicking a ball, or speaking a word are all controlled on purpose. But most of what the nervous system does, you never think about. It keeps your heart beating about 100,000 times a day. It tells your stomach to digest food. It pulls your hand off a hot stove before you even feel the pain. This automatic part is called the autonomic nervous system.

The brain is the most complex object scientists have ever studied. It has more connections inside it than there are stars in our galaxy. Even so, there is a lot we still do not understand. Scientists do not fully know how memories are stored, why we dream, or how the brain creates the feeling of being a person. Consciousness, the simple fact that you can feel yourself thinking, may be the biggest unsolved mystery in all of science.

You can take care of your nervous system. Sleep helps the brain clean out waste and lock in memories. Wearing a helmet during sports protects the brain and spinal cord, which do not heal well after big injuries. Reading, learning, and trying new things build new connections between neurons your whole life.