What can you do to keep your nervous system healthy?
By now you should realize that the nervous system controls just about everything your body does. We introduced the nervous system by discussing how NASA's Mission Control keeps track of everything involved in a space shuttle flight, detects errors, corrects them, and sends out instructions for all aspects of the flight plan. In a similar way, the nervous system is constantly gathering information about conditions inside and outside the body, evaluating this information, and sending commands to our organs, glands, and muscles. In addition, the nervous system enables us to learn, understand, remember, plan for the future, and behave in productive, creative ways. As you can imagine, there can be serious consequences both in terms of health of the body and in terms of behavior if the nervous system does not work properly. In this section you will learn what some of those consequences are and how to stay healthy.
Let's first review what we have learned about the nervous system. Then we will consider some problems that occur when the nervous system is sick, damaged, or not working well. It is important to realize that we are really just beginning to understand the brain. There is a lot we do not know. But it is important to use what we do know to keep our nervous systems as healthy as possible.
In this unit you have learned a lot about how the nervous system works. For example, you learned
- the nervous system is made up of billions of neurons that receive and send information.
- what the various parts of the cerebral cortex are and how they interpret information and send out nerve impulse messages.
- your brain receives information from sensory neurons and sends instructions back out through motor neurons.
- reflexes are the simplest type of circuit in the nervous system, and they exist to help the body function and protect it from immediate danger.
- how the eyes and ears code sights and sounds into nerve impulses that travel to the brain. It is in the brain that you experience sight and sound.
- how the brain coordinates movement.
Activity 7-1: Cortical Experiences
Many difficult tasks are accomplished by your brain. In this activity you review important functions of the brain and locate the parts of the brain responsible for those functions.
- Brain models such as “Big Brain on a Stick” and “Thinking Cap”
- Plastic wrap
- Washable markers (various colors)
- Activity Report
Step 1 Obtain a model of the brain, such as “Big Brain on a Stick,” described in Activity 2-1 and “Thinking Cap,” described in Activity 2-2. Cover your model with a layer of plastic wrap.
Step 2 Find the parts of the cortex responsible for each of the five senses: hearing, sight, smell, taste, and touch.
Step 3 Use a washable marking pen to label your model. Indicate the name of each region of the cerebral cortex and its function.
Step 4 Using your labeled model as a guide, complete the questions on the Activity Report.
Now that you learned about how your nervous system functions, let's investigate some of the problems that can affect your nervous system. What diseases and disorders disrupt the nervous system? How can you take good care of your nervous system and make its job easier?
Diseases and Disorders of the Nervous System
Think about the billions of cells in the nervous system and the complex structure of the brain. With all the information the nervous system handles every day, it's not surprising that sometimes things go wrong. Here are some of those things that can and do go wrong.
Many people suffer from headaches. The most common causes of headaches include infections and allergies in the eyes, ears, nose, or sinuses. Infections and allergies cause swelling and excess secretions, which put pressure on facial nerves and cause pain. Other causes of headaches include drinking too much alcohol, tumors, structural problems with blood vessels, or meningitis (inflammation of the meninges). Stress can cause headaches by making the muscles in the neck and back of the head tense. Remember that there are no pain sensors in brain tissue itself. There are pain sensors in the meninges however. Also, pain sensors are associated with the blood vessels going through the brain (see Figure 7.1.)
Figure 7.1 A migraine headache is a debilitating disorder of the nervous system.
Alzheimer's disease affects about four million people in the United States each year. Most of the victims are people over 65 years of age. The disease causes a huge loss of neurons in the brain. It also causes abnormal neuron structure that disrupts synapses and abnormal mineral deposits. The result is a gradual loss of brain function beginning with mild memory loss. When a person with Alzheimer's disease has trouble remembering things or moving around, the symptoms are sometimes dismissed as just a part of “getting old.” Eventually, people with Alzheimer's disease become unable to function at all. At the present time, there is no treatment for this disease.
Did You Know?
The National Institute of Aging estimates that hundreds of thousands of new cases of Alzheimer's disease may develop each year. This table shows the percentage of people in each age group that will develop the disease each year.
Percentage Developing Alzheimer's Each Year
Go to your library and find out how many people in the United States belong to each age group. With this information, calculate the number of people affected by Alzheimer's disease each year.
Mental Health Disorders
Many people suffer from disorders of the nervous system that dramatically influence or impair their behavior. These mental health disorders can appear in a variety of ways. Some mental health disorders are behavioral changes that are not very far from what would be considered normal. But others can make it impossible for a person to function in society. For example, we all feel sad, bored, or just down at times. But serious episodes of depression go beyond the normal ups and downs of everyday life. Persistent sadness and inability to take an interest in or enjoy normal activities can be a sign of serious or clinical depression. Depressed individuals may have frequent physical complaints such as headaches and stomach aches. They may also avoid normal situations such as school or work. Some people cycle between a state of depression and a state of mania characterized by abnormally high energy levels. In the manic state a person may go days without sleep. Manic depressive illness may be due to biochemical imbalances in the nervous system, and often can be treated with prescription drugs.
Another type of mental health disorder is anxiety. All of us feel nervous and anxious from time to time. It is entirely normal to feel that way before giving a presentation to your class or before a major athletic event. But sometimes anxieties can get so severe that they interfere with daily activities. Some people feel anxious in open spaces or in crowds. As a result, they cannot leave their homes and interact with other people. An abnormal fear and anxiety caused by a specific item or situation is called a phobia. Fear of open or public places is agoraphobia. There was a movie several years ago called Arachnophobia. Do you know what that means? A psychiatrist or clinical psychologist can help someone overcome anxieties and phobias.
Eating disorders are also mental conditions that can be helped by consultation with a specialist. Anorexia nervosa is characterized by an irrational fear of being fat. Consequently, the anorexic person develops a type of self-imposed starvation. Bulimia is another type of eating disorder. Bulimia is characterized by periods of excessive eating, called bingeing, which are followed by vomiting. Unfortunately, the number of cases of both anorexia nervosa and bulimia are increasing among teenage girls and young women in the United States. These eating disorders can be so severe that they cause serious malnutrition and even death. If you suspect one of your friends is tending toward one of these disorders, suggest that he or she seek help from a counselor or doctor who specializes in adolescent medicine.
Learning disabilities are another type of mental health disorder. Learning disabilities can be caused by nervous system problems with receiving, processing, or communicating information. Some learning disabled children are also hyperactive and have very short attention spans. Many people with learning disabilities, however, are extremely bright and may try very hard to follow instructions, concentrate, and do assigned tasks. But they simply may be incapable of keeping up. Learning disabilities affect as many as 15% of otherwise normal school children, and frequently with special help they can be overcome.
Mental disorders that are so severe that an individual cannot function in society are called psychoses. A person with a psychosis is not able to distinguish fact from fantasy. He or she may hear voices or hallucinate. A hallucination is seeing or hearing something that isn't there. It is caused by abnormal brain activity in parts of the brain that would normally receive the sensations that are being imagined.
Severe manic-depressive illness can be a psychosis. The most common psychosis among young people is schizophrenia. In initial stages, schizophrenia makes a person have strange thoughts, feelings, and behaviors. For example, a person may wash his or her hands time and time again or hear voices that aren't there. Paranoid schizophrenia is a condition in which the person thinks he or she is being followed, listened to, and spied upon. He or she is constantly afraid and knows that there are enemies everywhere. Try to imagine what it would be like to think that enemies are spying on everything you say or do and are constantly surrounding you. Schizophrenics can be cured, and can lead normal lives. People with the worst cases of psychoses, however, must be kept in appropriate medical facilities.
Figure 7.2 (Left) PET image of a healthy brain shows normal activity. (Right) PET image of a schizophrenic brain shows reduced activity, particularly in the frontal lobes regions involved in complex though processes.
Brain tumors and cancer are abnormal cell growths in the brain. A tumor is a mass of abnormal cells. The growth of a tumor creates swelling and pressure in the brain. The swelling and pressure can destroy healthy brain cells or prevent them from functioning effectively. Brain tumors or cancer can cause a wide range of problems but can be treated if discovered early enough.
Figure 7.3 MRI image of a brain-tumor patient reveals a tumor in the upper-right region of the brain.
Two types of strokes affect the brain. In one type of stroke, too little blood reaches a region of the brain. Another type of stroke is caused by a ruptured blood vessel, which bleeds into a brain area. Both kinds of stroke can destroy surrounding brain tissue. Brain damage from strokes can cause inability to move a body part and difficulty seeing, speaking, and communicating. For example, a person who has suffered a stroke may be unable to move one side of the face, while the other side remains normal. Because each side of the brain controls the opposite side of the body, a stroke on the left side of the brain affects the right side of the body.
Figure 7.4 In this cross section of a stroke patient's brain, a massive hemorrhage has caused swelling of the right hemisphere.
Brain Trauma/Spinal Cord Injuries
Some types of cells in your body do a good job of healing, such as your skin cells. But brain and spinal cord tissues are not so quick to heal. In fact, damage to neurons is usually permanent. In peripheral neurons, some regrowth of axons can occur. If the sensory nerves in your finger are damaged, they can regrow over a period of months, so that feeling in the finger returns. If part of the spinal cord is severed however, the connections between neurons are permanently destroyed. Messages cannot get past the severed area. As a result, a person with a spinal cord injury loses sensation and becomes paralyzed in the area below the spinal cord damage.
Learning More about Nervous System Disorders
Select one of the following nervous system disorders and do library research on it. Write a report to share your findings with the class.
- Tourette's Syndrome
- Attention Deficit
- Fetal Alcohol Syndrome
- Parkinson's Disease
- Depression/Syndrome Mania
- Down Syndrome
- Another topic approved by your teacher
Damage to brain cells is permanent. Since each lobe of the brain has different functions, the effects of brain damage depend on the area damaged. Although brain and spinal cord neurons do not heal, other parts of the brain and spinal cord can work to compensate for lost functions. Just as people without the use of their legs may more fully develop their arms and upper body, other brain regions can learn to take over some functions lost by brain damage. For example, someone who suffers speech loss because of damage to the left cerebral hemisphere can recover speech as the right hemisphere takes over.
Drug and Alcohol Addiction
Think back to the discussion about neurotransmitters. Remember that neurotransmitters are the chemicals that carry messages across the synapse, from one neuron to the next. Drugs, or any chemical, can affect your body by interfering with the neurotransmitters. Some illegal drugs, such as LSD, block receptors and prevent messages from crossing synapses. Others act like neurotransmitters or alter the actions of normal neurotransmitters.
Your brain helps you seek out the things that give you pleasure or make you feel good. For example, your brain makes you want to eat a good meal, get a good night's sleep, or exercise. When you succeed at a task such as playing a piece of music perfectly, hitting a home run, or getting an A on your science test, your brain makes you feel good. This desire to seek good feelings leads some people into drug addiction. A person might try drugs, enjoy the experience, and try it again. However, after a while, the brain begins to need the drugs. When that happens, living becomes very difficult without the drug. At the same time, the drugs can cause parts of the nervous system to work abnormally.
Cocaine is an example of one drug that causes addiction while damaging the brain. Cocaine causes a feeling of high energy or a “rush” because it blocks the re-uptake of a certain neurotransmitter called dopamine. The blocked re-uptake means that the transmitter stays in the synapse longer and stimulates the target cell more. The nervous system gradually readjusts itself so it releases less and less dopamine with each nerve impulse. Because less dopamine is being released, it takes more and more cocaine to get the same effect that a small dose had originally. Each time the drug wears off, the person feels worse because of abnormally low dopamine levels. Thus, the person craves more of the drug. Meanwhile, the drug is causing bad things to happen elsewhere in the brain. Cocaine causes decreased blood flow to the cerebral cortex for example. With repeated loss of its blood supply, cells in the cortex die and are lost forever. Cocaine users lose more and more brain capacity!
Each person's nervous system responds somewhat differently to drugs and alcohol. For example, one drink may not affect a person at all, but may make another person half-drunk. One dose of a drug may barely affect a person, but kill another. Keep in mind that in addition to being addictive, drugs can permanently damage your brain. Drugs can destroy brain cells or the connections between them. The blood-brain barrier does not protect the brain from chemical damage-only your behavior can.
Alcohol changes the chemistry of every cell in your body. You are particularly sensitive to changes in the cerebellum. Drinking can make you lose your coordination and balance. Some people become louder and more aggressive when drinking. Others tend to become more quiet and moody. People who drink frequently over long periods of time can become alcoholics. Alcoholics are addicted to alcohol in much the same way as many drug users are addicted to drugs. In addition to destroying brain cells, alcohol destroys other vital organs, such as the liver.
Drug and alcohol use by pregnant women can cause serious problems for the unborn child. If a pregnant woman uses drugs, her child may be born addicted or brain damaged. Children born to alcoholic mothers have smaller cortexes. Their neurons and connections between parts of the brain are poorly developed. As a result, these children have a range of problems known as fetal alcohol syndrome. Children with fetal alcohol syndrome may be physically deformed and/or mentally retarded.
Cerebral palsy is caused by damage to the motor area of the brain during pregnancy, childbirth, or infancy. Damage to the motor area of the brain causes poor muscle control and lack of coordination. People with cerebral palsy sometimes also have poor hearing and communication skills. Many people with cerebral palsy have no other mental disabilities, attend regular schools, and are very smart. Computers can help people with cerebral palsy overcome difficulties of communication. Cerebral palsy cannot get worse over time, and in some cases surgery can help lessen the effects of poor muscle control.
Every person's nervous system is unique-like a fingerprint. Your nervous system may be better at some things than another person's. The challenge lies in finding those things you're naturally good at and developing those talents. A big part of developing your natural abilities is learning to take care of yourself. Since your nervous system takes part in everything you do, your actions and behavior can directly affect its functions. Learning to take care of your body will enable you to get your body to perform at its best. Let's review some of the basics in caring for your nervous system.
Did You Know?
Your brain has a biological clock in the hypothalamus that tells you when it is time to sleep and time to wake up. If the cells that make up this clock are damaged in an animal, that animal will be just as likely to sleep, wake, eat, and drink at any time of day. It will have no daily rhythms. When people take plane trips across many time zones, the brain's clock is still running on home time. This can cause a problem called jet lag until the brain clock can be reset to local time.
Figure 7.5 What would you make of the daily rhythms of these teens?
Did You Know?
There are two kinds of sleep: REM sleep and non-REM sleep. REM stands for rapid eye movements. During REM sleep you have vivid dreams and your eyes dart back and forth under your eyelids as if you are watching the events in your dream. Your body doesn't move to act out the dream because your brain inhibits the motor neurons in your spinal cord. During REM sleep your EEG looks like your brain is awake! During non-REM sleep the EEG is different; the brain is quieter and you do not have vivid dreams. When you first go to sleep, you are in deep non-REM sleep. Only about 20% of sleep is REM sleep.
Sleep directly affects how your nervous system functions. Chemical substances in the brain cause you to feel sleepy and to wake up. When you don't get enough sleep, you may feel drowsy, uncoordinated, and forgetful. You can't think properly. If you read something, you forget it. Why? Sleep not only provides time for your muscles to rest, it provides essential restoration for your brain. When you do not get enough sleep, you accumulate a sleep debt that must eventually be paid back. It may cause you to fall asleep at times when you shouldn't, such as in class and at a movie. Falling asleep while driving is one of the biggest causes of traffic fatalities.
No one knows for sure what the function of sleep is, or how it affects our behavior. Some people need more sleep; others need less. The brain, heart, lungs, and even muscles continue to function during sleep. The brain, in fact, goes through cycles of activity and inactivity during sleep. While you sleep, you have periods of deep, dreamless sleep and periods of light, dream-filled sleep. Some scientists think that sleep provides time for the brain to process information from the day. The brain can make new connections between neurons based on important information, and throw out unimportant information. Other scientists think that sleep restores the energy reserves of the brain.
How Much Sleep Do You Need?
For two weeks, keep track of how much sleep you get by recording the times you fall asleep and wake up. Make a note each day of your physical and mental energy levels. After two weeks, study your notes and see if there are any correlations between sleep and performance. Where could you go to find more information about this topic?
Did You Know?
Some scientists think that more than half of what we learn during our whole lives happens in the first six to seven years.
What Do You Think?
- Is the mind the same thing as the brain? Explain.
- What preparation would you recommend to a friend who is taking a test, giving a presentation, or writing a paper? You want to help her keep her mind sharp. What should she do the night before and the day before?
“What is mind? No matter. What is matter? Never mind.”
-Thomas Hewitt Key
You may have heard the phrase “use it or lose it.” For example, you have to use your muscles to keep good muscle tone. The same thing applies to your brain. When you use your brain, you stimulate electrical activity. When you learn new things, your brain develops new connections. The more you use your brain, the more connections your neurons keep making. If you don't use your brain, these connections can weaken or disappear. You gradually lose neurons as you age. Some scientists think that if you keep your brain active, you stay more mentally alert. Since you lose brain cells every day, you might as well put them to use while you have them!
Memory is another function of your cortex. Memory and learning are closely related. To learn, you need to be able to remember, but too much memory could make it hard to learn. Suppose you remembered everything you ever read or did. Some people can. Some people, called savants, have special memory abilities for very limited topics. For example, they may remember all of the numbers in a phone book or all of the baseball scores from games played over many years.
Activity 7-2: Improving Your Memory
How is it possible to improve memory? Since a good memory makes learning easier, it is helpful to discover how you can improve your memory. In this activity you investigate some ways to improve your memory.
Step 1 One way to improve your memory is to make connections between the things you have to remember or between what you want to remember and what you already know. Some ways of making connections include creating stories, pictures, songs, or mnemonic (nee-MAHN-ik) devices. Remember that making connections is important as you read the list of words below.
- swimming pool
Step 2 Think about how you could connect or relate these words so they would be easier to remember. Discuss these methods with your lab partners and create a team list of suggestions for making connections. Record this list on the Activity Report.
Step 3 Select the method that you prefer and record it on the Activity Report.
Step 4 Using your preferred memory method, look again at the list and concentrate on remembering the items on the list.
Step 5 Cover up the list and use the space provided on the Activity Report to write down the words from memory. When you have finished, check the original list to see how many words you remembered correctly. Write down your score by the list.
Step 6 Think about this memory method and how well it worked for you. Was it effective? Could it have been more effective? How? Record your comments and complete the remaining items on the Activity Report.
You Are Unique
Why can . . .
- some people have perfect pitch and sing any song but not have good balance?
- some people play trombone but not play basketball?
- some people do math in their heads and play chess but can't write a story or paint a picture?
Your nervous system is amazing. It is made up of billions of neurons and many kilometers of axons and dendrites. Enough electricity moves through your nervous system to light a 10-watt bulb. Your brain weighs 1.4 kilograms (a little more than 3 pounds) and is responsible for making you who you are. No one else's brain or nervous system works quite like yours.
Although people have been studying the brain for thousands of years, many questions remain. The National Science Foundation named the 1990s the Decade of the Brain. In the 1990s, scientists have learned more about the brain than in all previous years combined. But the brain is such a complex organ that it seems we have only scratched the surface in what we understand.
Activity 7-3: Your Nervous System in Action
Are you aware of the many difficult tasks your brain accomplishes? In this activity you have the opportunity to explore some of the important actions of your nervous system. Then you apply what you have learned to some situations in daily life.
- Models of the brain (“Brain on a Stick” and “Thinking Cap”)
- Activity Report
Step 1 Place your text, the “Brain on a Stick” model, and the “Thinking Cap” in front of you.
Step 2 Discuss each question on the Activity Report with a lab partner. Use the text, including Figure 1.2, and your models as references.
Step 3 Complete the Activity Report.
As you study, walk, or bike at school today, think about the electrical impulses running up and down your body. Think about the sensory neurons sending messages to your brain and the motor neurons firing to keep you moving. While you're at it, consider all the nervous system functions you're not even aware of. Your brain is a wondrous part of your incredible nervous system. Enjoy it and take good care of it!
- Sample answers to these questions will be provided upon request. Please send an email to email@example.com to request sample answers.
- Name and describe three brain/nervous system disorders.
- Name three ways drugs or alcohol can affect the nervous system.
- Why is drug use of such concern?
- Describe four ways you can take care of your nervous system.
- List three “fun facts” you've learned about the brain and nervous system that you didn't know before you read this unit.