The brain has three major parts – the cerebrum, the cerebellum and the brain stem. The brain stem connects the spinal cord and the brain. It controls functions that keep people alive such as breathing, heart rate, blood pressure and food digestion. Those activities occur without any thought.

Things are different in the cerebellum. That region controls voluntary movement. When you want to lift your fork or wave your hand, you form the thought and then an area in the cerebellum translates your will into action.

Neurons, the basic functional units of the nervous system, are three-part units and are key to brain function. They are comprised of a nerve cell body, axon and dendrite, and they power the rapid-fire process that turns thought into movement. The thought moves as an electrical signal from the nerve cell down the axon to a dendrite, which looks like branches at the end of nerve cells. The signal jumps from the end of the dendrite on one cell across the space, called a synapse, to the dendrite of another cell with the help of chemicals called neurotransmitters. That signal continues jumping from cell to cell until it reaches the muscle you need to wave, wink or walk.

The cerebrum is the largest of the three brain sections, accounts for about 85 percent of the brain's weight, and has four lobes. The lobes-frontal, parietal, temporal and occipital -- each have different functions. The parietal lobe helps people understand what they see and feel, while the frontal lobe determines personality and emotions. Vision functions are located in the occipital lobe, and hearing and word recognition abilities are in the temporal lobe.

Because the brain's healthy functioning is essential to living and determines quality of life, doctors emphasize protecting the organ from injury and chemical abuse.

There is a consensus among researchers that brain cells regenerate throughout life, said Doug Postels, a pediatric neurosurgeon in New Orleans, but that new growth happens very slowly after a certain age. "The size of the brain doesn't increase much after 3," Postels explains.

During the first three years of life, the brain experiences most of its growth and develops most of its potential for learning. That's the time frame in which synaptogenesis, or the creation of pathways for brain cells to communicate, occurs. Doctors generally accept that cut-off point for two reasons, Postels said. First, in situations where doctors removed parts of the brains of patients younger than 3 to correct disorders, the remaining brain sections developed to assume the role of the portions those doctors removed. But when physicians performed the same surgery on older patients, that adaptability function did not occur. Second, "We know from experiments that if you deprive people of intellectual stimulation and put them in a dark room, that it produces permanent changes in the brain," Postels said. "That occurs most dramatically before age 3. After that age, it's impossible to ethically do a study."

Previous research produced information about the effects of stimulation deprivation, but modern ethical guidelines prohibit such research on people because of the potentially harmful outcome.

Because so little recovery occurs to brains damaged after age 3, the effects of drugs and alcohol on the brain might be lasting. Doctors know what inhalants, steroids, marijuana, cocaine and alcohol do to the brain when people use them. "The question scientists can't answer now is if the damage is permanent," said Sue Rusche, co-author of "False Messengers," a book on how addictive drugs change the brain.

Inhalants, such as glue, paint, gasoline and aerosols, destroy the outer lining of nerve cells and make them unable to communicate with one another. In 1993, more than 60 young people died from sniffing inhalants, according to National Families in Action, a drug education center based in Atlanta.

Studies have found that marijuana use hinders memory, learning, judgment and reaction times, while steroids cause aggression and violent mood swings.

Ecstasy use is rising among young people, Rusche said, and scientists have found that drug destroys neurons that make serotonin, a chemical crucial in controlling sleep, violence, mood swings and sexual urges. While doctors and scientists know about some effects drugs have on the brain, they don't have a full picture, Rusche said.

"When people start using a drug, the scientists know nothing about it. These people are volunteering to be guinea pigs," said Rusche, who is co-founder and executive director of National Families in Action. "Once enough people take it, scientists apply for grants and start studying it. People are inventive. They find new drugs or new ways to take old drugs-like crack from cocaine. "There's a lot we won't know about until later," she said. "The classic example is cigarettes. We allowed people to smoke for 100 years before we knew about all the horrible things that nicotine will do.

I. Mind Map

II. Mind Gym

I. Identify which part of the brain does the following side fall.

II. Answer the following questions briefly.