CK-12 Life Science

by CK-12 Foundation

  semicircular canals

  Liquid-filled part of the ear that senses changes in position and generates nerve impulses in response.

  stirrup

  Last of three tiny bones that pass vibrations through the ear.

  taste buds

  Tiny bumps on the tongue that contain taste neurons.

  touch

  Sense of pain, pressure, or temperature.

  Points to Consider

  Our senses, along with the rest of our nervous system, help us stay safe. At least they do if our nervous system is healthy. But what if the nervous system itself becomes ill or injured? What do you think would happen then? How do you think nervous system problems affect the rest of the body?

  Lesson 20.4: Health of the Nervous System

  Lesson Objectives

  Describe diseases of the nervous system.

  Explain how the nervous system can be injured.

  Identify the dangers of alcohol and other drugs.

  List ways to keep the nervous system healthy.

  Check Your Understanding

  What is the role of the nervous system?

  What are some of the components of the nervous system?

  Introduction

  The nervous system controls sensing, feeling, and thinking. It also controls movement and just about every other body function. That’s why problems with the nervous system can affect the entire body. Nervous system problems include diseases and injuries. Most nervous system diseases cannot be prevented. However, you can take steps to reduce your risk of nervous system injuries.

  Nervous System Diseases

  Diseases of the nervous system include brain and spinal cord infections. Other problems of the nervous system range from very serious diseases, such as tumors, to less serious problems, such as tension headaches. Some diseases are present at birth. Others begin during childhood or adulthood.

  Central Nervous System Infections

  When you think of infections, you probably think of an ear infection or strep throat. You probably don’t think of a brain or spinal cord infection. However, bacteria and viruses can infect these organs as well as other parts of the body. Infections of the brain and spinal cord are not very common. But when they happen, they can be very serious. That’s why it’s important to know their symptoms.

  Encephalitis is a brain infection. If you have encephalitis, you are likely to have a fever and headache or feel drowsy and confused. The disease is most often caused by viruses. and the immune system tries to fight off a brain infection, just as it tries to fight off other infections. However, this can do more harm than good. The immune system’s response may cause swelling in the brain. With no room to expand, the brain pushes against the skull. This may injure the brain and even cause death. Medicines can help fight some viral infections of the brain. Others just have to run their course.

  Meningitis is an infection of the membranes that cover the brain and spinal cord. If you have meningitis, you are likely to have a fever and headache. Another telltale symptom is a stiff neck. Meningitis can be caused by viruses or bacteria. Viral meningitis often clears up on its own after a few days. Bacterial meningitis is much more serious (Figure below). It may cause brain damage and death. People with bacterial meningitis need emergency medical treatment. They are usually given antibiotics to kill the bacteria.

  Figure 20.33

  These bacteriashown at more than 1,000 times their actual sizeare the cause of bacterial meningitis; despite their tiny size, they can cause very serious illness.

  A vaccine to prevent meningitis recently became available. It can be given to children as young as 2 years old. Many doctors recommend that children receive the vaccine no later than age 12 or 13, or before they begin high school.

  A condition called Reye’s syndrome can occur in young people that take aspirin when they have a viral infection. The syndrome causes swelling of the brain and may be fatal. Fortunately, Reye’s syndrome is very rare. The best way to prevent it is by not taking aspirin when you have a viral infection. Products like cold medicines often contain aspirin. Therefore, it’s important to read labels carefully when taking any medicines (Figure below).

  Figure 20.34

  Since 1988, the U.S. Food and Drug Administration has required that all aspirin and aspirin-containing products carry this warning label.

  Other Nervous System Diseases

  Like other parts of the body, the nervous system may develop tumors. A tumor is a mass of cells that grow out of control. A tumor in the brain may press on normal brain tissues. This can cause headaches, difficulty speaking, or other problems, depending on where the tumor is located. Pressure from a tumor can even cause permanent brain damage. In many cases, brain tumors can be removed with surgery. In other cases, tumors can’t be removed without damaging the brain even more. In those cases, other types of treatments may be needed.

  Cerebral palsy is a disease caused by injury to the developing brain. The injury occurs before, during, or shortly after birth. Cerebral palsy is more common in babies that have a low weight at birth. However, the cause of the brain injury is not often known for certain. The parts of the brain that control body movements are usually affected. Symptoms range from weak muscles in mild cases, to trouble walking and talking in more severe cases. There is no known cure for cerebral palsy.

  Epilepsy is a disease in which seizures occur. A seizure is a period of lost consciousness that may include violent muscle contractions. It is caused by abnormal electrical activity in the brain. The underlying cause of epilepsy may be an infection, brain injury, or tumor. The seizures of epilepsy can often be controlled with medicine. There is no known cure for the disease, but children with epilepsy may outgrow it by adulthood.

  A headache is a very common nervous system problem. Headaches may be a symptom of serious diseases such as brain tumors or encephalitis. More commonly, they are due to muscle tension. A tension headache occurs when muscles in the shoulders, neck, and head become too tense. This often happens when people are “stressed out.” Just trying to relax may help relieve this type of headache (Figure below). Mild pain relievers such as ibuprofen may also help.

  Figure 20.35

  Sometimes relaxation is the best medicine for a tension headache, and to help muscles get rid of pain.

  A migraine is a more severe type of headache. It occurs when blood vessels in the head dilate, or expand. This may be triggered by certain foods, bright lights, weather changes, or other factors. People with migraines may also have nausea or other symptoms. Fortunately, migraines can often be relieved with prescription drugs.

  There are many other nervous system diseases. They include multiple sclerosis, Huntington’s disease, Parkinson’s disease, and Alzheimer’s disease. However, these diseases rarely, if ever, occur in young people. Their causes and symptoms are listed in Table (below). The diseases have no known cure, but medicines may help control their symptoms.

  Other Diseases of the Nervous System Disease Cause Symptoms

  Multiple Sclerosis The immune system attacks and damages the central nervous system so neurons cannot function normally. Muscle weakness, difficulty moving, problems with coordination, difficulty keeping the body balanced

  Huntington’s Disease An inherited defective gene codes for an abnormal protein that causes the death of neurons. Uncontrolled jerky movements, loss of muscle control, problems with memory and learning

  Parkinson’s Disease An abnormally low level of a neurotransmitter affects the part of the brain that controls movement. Rigid muscles, uncontrolled shaking, slowed movements, problems with speaking

  Alzheimer’s Disease Abnormal changes in the brain cause the gradual loss of most normal brain functions. Memory loss, confusion, mood swings, gradual loss of control over mental and physical abilities

  Injuries to the Central Nervous System

  Injuries to the central nervous system may damage tissues of the brain or spinal cord. If an injury is mild, a person may have a
full recovery. If an injury is severe, it may cause permanent disability or even death. Brain and spinal cord injuries most commonly occur because of car crashes or sports accidents. The best way to deal with such injuries is to try to prevent them.

  Brain Injuries

  The mildest and most common type of brain injury is a concussion. This is a bruise on the surface of the brain. It may cause temporary problems such as headache, drowsiness, and confusion. Most concussions in young people occur when they are playing sports, especially contact sports like football. A concussion normally heals on its own in a few days. A single concussion is unlikely to cause permanent damage. However, repeated concussions may lead to lasting problems. People that have had two or more concussions may have life-long difficulties with memory, learning, speech, or balance. You can see an animation of a how a concussion occurs by visiting http://pennhealth.com/health_info/ animationplayer/concussion.html.

  A person with a serious brain injury usually suffers permanent brain damage. As a result, the person may have trouble talking or controlling body movements. Symptoms depend on what part of the brain was injured. Serious brain injuries can also cause personality changes and problems with mental abilities such as memory. Medicines, counseling, and other treatments may help people with serious brain injuries recover from—or at least learn to cope with—their disabilities.

  Spinal Cord Injuries

  Spinal cord injuries interrupt messages between the brain and body. They may cause a person to lose the ability to feel or move parts of the body. This is called paralysis. Whether paralysis occurs—and what parts of the body are affected if it does—depend on the location and seriousness of the injury. In addition to car crashes and sports injuries, diving accidents are a common cause of spinal cord injuries.

  Some people recover from spinal cord injuries. However, many people are paralyzed for life. Thanks to the work of Christopher Reeve (Figure below), more research is being done on spinal cord injuries now than ever before. For example, scientists are trying to discover ways to regrow damaged spinal cord neurons.

  Figure 20.36

  Former star, Christopher Reeve, was paralyzed from the neck down in a fall from a horse; the injury crushed his spinal cord so his brain could no longer communicate with his body.

  Dangers of Alcohol and Other Drugs

  A drug is any chemical substance that affects the body or brain. Some drugs are medicines (Figure below). Although these drugs are helpful when used properly, they can be misused like any other drugs. Drugs that aren’t medicines include both legal and illegal drugs. Examples of legal drugs are alcohol and caffeine. Although these drugs can be used legally by adults, they can still do harm. Examples of illegal drugs include marijuana and cocaine.

  Figure 20.37

  Drugs that are prescribed by a doctor can be misused just like illegal drugs.

  Types of Psychoactive Drugs

  Drugs like alcohol, marijuana, and cocaine affect the brain. Drugs that affect the brain are called psychoactive drugs. They influence how a person feels, thinks, or acts. You can watch animations of psychoactive drugs and the brain at http://www.pbs.org/wnet/closetohome/science/html/animations.html.

  If you think you have never used a psychoactive drug, think again. Do you drink soft drinks, such as colas? Most of them contain caffeine, which is a psychoactive drug. Caffeine is also found in coffee and chocolate (Figure below).

  Figure 20.38

  All three of these popular products contain the stimulant drug caffeine.

  Caffeine is an example of a class of psychoactive drugs called stimulant drugs. Other classes of psychoactive drugs are depressant drugs and hallucinogenic drugs. Drugs are classified based on how they affect the nervous system.

  A stimulant drug is a psychoactive drug that speeds up the nervous system. This type of drug may make people feel more alert. Stimulants also increase heart rate and blood pressure. High doses of stimulant drugs can be dangerous. They can even cause death. Other stimulant drugs include nicotine (in tobacco) and cocaine.

  A depressant drug is psychoactive drug that slows down the nervous system. This type of drug may make people feel calm and drowsy. It also decreases heart rate and the rate of breathing. High doses of depressant drugs can be dangerous. They may slow down the nervous system so much that heartbeat and breathing stop. Examples of depressant drugs include alcohol and morphine.

  An hallucinogenic drug is a psychoactive drug that can cause strange sensations, perceptions, and thoughts. Examples of hallucinogenic drugs include marijuana and LSD.

  Drug Abuse

  Psychoactive drugs, both legal and illegal, are often abused. Drug abuse is the use of a drug without the advice of a doctor or for reasons other than those for which the drug was intended. Drug abuse may lead to physical dependence on the drug. This occurs when drug abusers need a drug to feel well physically. If they stop using the drug, they may experience symptoms like vomiting, diarrhea, or depression. This is called withdrawal. Drug abuse may also lead to psychological dependence. This occurs when drug abusers need a drug to feel well emotionally and mentally.

  For some drug abusers, a drug takes over their life. Their thoughts and activities revolve around getting and using the drug. No matter what the consequences, they keep using the drug. Even if they want to stop using the drug, they can’t. When drug abuse reaches this state, it’s called drug addiction. Alcohol, nicotine, and cocaine are all highly addictive drugs.

  People that are addicted to a drug may need to take more of the drug to feel the same effects as when they first started using the drug. This is called tolerance. People that develop tolerance are at risk of a drug overdose. A drug overdose occurs when someone takes so much of a drug that it causes serious illness or death.

  Keeping the Nervous System Healthy

  There are many choices you can make to keep your nervous system healthy. One obvious choice is to avoid using alcohol or other drugs. Not only will you avoid the injury that drugs themselves can cause. You will also be less likely to get involved in other risky behaviors that could harm your nervous system.

  Another way to keep the nervous system healthy is to eat a variety of healthy foods. The minerals calcium and potassium and vitamins B1 and B12 are important for a healthy nervous system. Some foods that are good sources for these minerals and vitamins are shown Figure below.

  Figure 20.39

  These foods are sources of nutrients needed for a healthy nervous system.

  Daily physical activity is also important for nervous system health. Regular exercise makes your heart more efficient at pumping blood to your brain. As a result, your brain gets more oxygen, which it needs to function normally.

  The saying “use it or lose it” applies to your brain as well as your body. This means that mental activity, not just physical activity, is important for nervous system health. Doing crossword puzzles, reading, and playing a musical instrument are just a few ways you can keep your brain active.

  You can also choose to practice safe behaviors to protect your nervous system from injury. To keep your nervous system safe, choose to

  Wear safety goggles or sunglasses when needed to protect your eyes from injury.

  Wear hearing protectors such as ear plugs to protect your ears from loud sounds.

  Wear a safety helmet for activities like bike riding and skating (Figure below).

  Wear a safety belt every time you ride in a motor vehicle.

  Avoid unnecessary risks, such as performing dangerous stunts on your bike.

  Never dive into water that is not approved for diving. If the water is too shallow, you could seriously injure your brain or spinal cord. A few minutes of fun could turn into a lifetime in a wheelchair.

  Figure 20.40

  Bicycle helmets help protect from head injuries; making healthy choices like this can help prevent nervous system injuries that could cause lifelong disability.

  Lesson Summary

  The nervous system can be affect
ed by infections, tumors, and other diseases.

  Brain or spinal cord injuries may cause permanent disability or even death.

  The use of psychoactive drugs can lead to drug abuse or addiction.

  You can make choices that will help keep your nervous system healthy and safe.

  Review Questions

  What is encephalitis?

  What causes muscle weakness in cerebral palsy?

  List symptoms of a concussion.

  Define psychoactive drug and name two examples.

  List three choices you can make to keep your nervous system healthy.

  Explain why young people should not take aspirin when they have the flu, which is caused by viruses.

  Compare and contrast tension headaches and migraine headaches.

  Explain what causes paralysis.

  Which type of psychoactive drug is caffeine? How does caffeine affect the nervous system?

  How is drug tolerance related to drug overdose?

  Further Reading / Supplemental Links

  CK12 High School Biology, Chapter 35.

  Connie Goldsmith. Meningitis. Twenty First Century Books, 2007.

  David Aretha. On the Rocks: Teens and Alcohol. Franklin Watts, 2007.