Drugs and alcohol affect the central nervous system, which simply put is made up of your brain and all the nerves that connect muscles and organs of your body to your brain. Nerves carry messages from your brain to your body to tell it to move your fingers, digest your supper, breathe and pump blood. Nerves also carry messages back to your brain from your senses such as sight, touch, sound, smell, taste, pain, and whether you are feeling warm, cold, full after eating a meal, or the need to urinate. Your brain and nerves are made up of cells called neurons. Within your brain neurons connect to other neurons and fire messages back and forth constantly. They carry your thoughts and feelings.
Drugs and alcohol imitate or interfere with the messages within your brain and between your brain and your body. Alcohol can slow down the messages between your brain and muscles, making your leg slower to respond to an emergency and slower to get to the brake pedal of your car. Cocaine can speed messages within the brain up, making you feel more awake and full of energy. Marijuana mixes everything up, sometimes speeding up messages and sometimes slowing down messages, confusing your brain. Heroin slows down messages and blocks the pain message from travelling from your body to your brain.