The average brain weights 3 pounds and has around 100 billion cells called neurons. Each neuron is connected to about 10,000 others. Altogether, you have about 1,000 trillion! Your brain controls almost everything in your body; how you move, what you see, hear, feel, and allows you to learn by putting all of this information together. If your brain becomes damaged from an accident or illness, it can affect you in many different ways. There are three main parts of your brain, the forebrain, cerebellum and brainstem. There are also nerves that make up your spinal cord that go down your back. Nerves run all through your body.

Forebrain

Your forebrain has the cerebrum on the outside and several other small parts on the inside.  The cerebrum is what most people think of when you talk about the brain. Your cerebrum has two halves that are connected by a large cord that it uses so that they can share information. Each half controls a different function of your body, so that the right side of your cerebrum controls the left side of your body and the left side of your cerebrum controls the right side of your body. In most people, the left side is important for talking, using numbers and reasoning. The right side is more important for feelings, remembering faces and music.  The parts on the inside of the forebrain help control body temperature, thirst, hunger, smell, feelings and sleep.

Cerebellum Your cerebellum is located in the back of the brain, just under the cerebrum. It looks like a wrinkled ball of tissue. It controls body movements and balance. It does this by helping muscles work together, which allow you to stand without falling, play a piano or hit a ball with a bat. Brainstem Your brainstem is the bottom of the brain and connects to the spinal cord. Your brainstem takes the messages from the spinal cord and sends it to the forebrain. It also controls muscles that move without you thinking about it, like breathing and how fast your heart beats.

Spinal cord

Your spinal cord is connected to, but not part of the brain.  It carries messages that go from the brain to the nerves throughout the body or messages that go from these nerves to the brain. The messages from nerves found in your head and face do not travel through the spinal cord, but instead go directly to the brain. Spinal cords allow for you to respond quickly to a pain. When you touch a hot object with your hand a pain message goes from your hand to your spinal cord and turns around without going to your brain, to send a message to the muscles in your arm to pull your hand away.

Peripheral nerves

Nerves found throughout your body are called peripheral nerves. There are two main types of peripheral nerves. Some peripheral nerves carry messages from your body to your brain, such as messages that tell you to feel pain or cold. Other peripheral nerves carry messages from you brain to organs in your body, such as messages that tell your muscles to move or sweat glands to sweat.

Neurons

Your nerves are made of cells called neurons. Neurons get messages and send them to other neurons; these messages travel through many neurons from many different parts of your body. There are different sizes of neurons depending on where they are in your body. Arms and legs have the longest and the brain has the shortest. A neuron is like an on/off switch that you use to control a lamp in a room.

A neuron has a cell body with branches on it called dendrites, and a long wire-like part called an axion. A message is started when a special chemical touches the dendrite.  This chemical causes electricity to move along the axion.  At the end of the axion the electricity makes the neuron squirt out a chemical that jumps across a small space where it goes to another neuron's dendrite and starts a massage in the second neuron.  The message gets passed on from neuron to neuron, like the baton in a relay race. When you pick up an ice cube, the message of cold goes from the neurons in your fingertips, through your arm to your spinal cord. From your spinal cord, the message goes to your brain stem and into your cerebrum. If you think that you want to put the ice cube down, then the brain sends a message back down to the neurons in the muscles of your arm and fingers, to make them put the ice cube down.

You use your eyes, ears, mouth, nose and skin to gather information about the outside world. You can see, hear, taste, smell and touch things. You can also feel pain, pressure, temperature, and the position and movement of your body. All of this information is changed into electrical and chemical signals and carried to your brain that then puts all the information together to produce the whole picture. What you see and hear does not go through the spinal cord. It goes straight to the brain.

Source:http://www.neuroinitiative.org || http://www.tbiguide.com/howbrainworks.html || http://www.sciencemuseum.org.uk/exhibitions/brain/1.asp