Your brain at-a-glance.

* There are no two ways about it--drugs change the way the brain works. And the brain has some pretty heavy responsibilities, controlling body functions such as breathing, walking, and thinking. Here is a brief overview of the major parts of your brain and the jobs they do, along with some examples of how drugs can get in the way. After reading it, complete the diagram activity below.

The largest part of your brain is the cerebral cortex. When it's functioning normally, this section takes care of thinking, reasoning, the five senses, and controlling certain kinds of movements. But, smoking marijuana can make it tough for the cerebral cortex to do its work.

Next, making up only one eighth of the brain's total weight, is the cerebellum. The cerebellum is in charge of coordinating movements involved in repeated, everyday actions, such as brushing teeth and riding a bike. One of the health risks of abusing inhalants is that they may damage this part of the brain.

Just above the spinal cord, a small section of your brain called the brain stem controls basic functions, such as breathing, digesting food, and maintaining your heartbeat. Taking heroin can slow breathing--even to the point of death--because it affects the brain stem.

Then, there's the limbic system, also known as the emotional brain. This is where feelings like fear and passion are born. Many scientists believe that steroids act on the limbic system and cause some users to experience out-of-control feelings of violent aggression called roid rage.

Scientists have identified a reward pathway in the brain that includes the nucleus accumbens. When we do something that is key to survival, such as eating when we are hungry, the reward pathway is stimulated. Most drugs that are addictive, like cocaine, also stimulate this reward pathway, often more than natural rewards, such as food. Our brains are wired to remember what activates this pathway. That is why when we are hungry, we may crave food, and when a drug abuser's brain gets used to drugs, he or she craves drugs as well.

How can drugs do this? Once in the brain, drugs of abuse are similar in size and shape to brain chemicals called neurotransmitters. Brain cells release and absorb these natural chemicals in order to send and receive messages to and from each other. Drugs disrupt this delicate communication system. For example, nicotine causes more neurotransmitters to be released and cocaine blocks the normal reabsorption of brain chemicals. That is how the drugs produce unnatural feelings. While the feelings may last for minutes, the changes to brain cells in the reward pathway can be long-lasting.

Brain, p. 2: Cerebral cortex: thinking, reasoning, seeing, hearing, sense of touch, and some kinds of movement; Limbic system: produces feelings and emotions; Cerebellum: coordinates movements involved in everyday tasks; Brain stem: controls breathing, food digestion, and heartbeat; Nucleus accumbens: involved in reward and feelings of pleasure. Students' responses to how they've used each part of the brain will vary.