Section 11.3 Your Nervous System Objectives Explain the functions of the nervous system and the role of neurons. Describe the roles of the central nervous system and the peripheral nervous system. Identify the most important thing you can do to keep your nervous system healthy.

Health Stats This graph compares bicycle-helmet use and seat-belt use among teens. Why do you think many more teens wear seat belts than bicycle helmets?

What Is the Nervous System? Your nervous system receives information about what is going on inside and outside of your body. Then it processes the information and forms a response to it. The basic unit of the nervous system is a type of cell called a neuron (NOOR ahn).

Neuron Structure Neurons carry messages, or impulses, from one part of your body to another. A neuron has three basic parts. dendrites a cell body an axon

Types of Neurons Sensory Neurons Information about your external and internal environment is gathered by sensory neurons through your sense organs or other parts of your body. Interneurons Located only in the brain and spinal cord, interneurons pass impulses from one neuron to another. Motor Neurons Motor neurons send nerve impulses to muscles and glands.

Neuron Structure Dendrite Dendrites carry nerve impulses toward a neuron’s cell body. Cell Body The cell body controls the cell’s basic functions. Synapse The junction between an axon and another cell is a synapse. Chemicals called neurotransmitters pass the impulse from the sending neuron to the receiving cell. Axon Impulses travel along axons toward other cells. Myelin Sheath Some axons are covered by a myelin sheath that increases the speed of an impulse.

Central Nervous System The nervous system consists of two major divisions—the central nervous system and the peripheral nervous system. The central nervous system is the control center of the body. It includes the brain and spinal cord. The peripheral nervous system includes all the other parts of the nervous system.

The Brain The cerebrum consists of several specialized regions that receive messages from sense organs, and control movement, memory, communication, and reasoning. The cerebellum (sehr uh BEL um) coordinates your body’s movements and helps you keep your balance. The brain stem consists of three structures—the midbrain, pons, and medulla. These structures control many of your body’s involuntary actions.

Mixed Messages Test how well your brain can handle conflicting messages. Material watch or clock with second hand Try This Read the list of words while your partner times how long it takes you. Notice that the words in the list are written in different colors. This time you should say the color of each word as your partner times you. Do not read the words, rather, identify their colors.

Mixed Messages

Mixed Messages Think and Discuss Did it take you more time to read the words or say the colors? Describe the experience of saying the colors. Which part of your brain most likely works hardest during this activity? Which task is your brain better at—reading the words or identifying their colors? Once people master basic skills such as tying shoes or reading, they perform them with little thought. How do you think this fact affected your results in this activity? What do you think would happen if you asked a young child who has just learned to read to do this activity? Explain.

The Spinal Cord The spinal cord is a thick column of nerve tissue that links the brain to most of the nerves in the peripheral nervous system. The spinal cord extends from the brain down the back. Spinal nerves are part of the peripheral nervous system.

Reflexes An automatic response to your environment is called a reflex. In some reflex actions, the actions of the skeletal muscles are controlled by the spinal cord only—not the brain. Reflexes help protect your body from harm because they enable you to react very quickly.

A Reflex Action Sensory neurons in your hand send impulses to your spinal cord. A Reflex Action Neurons in your spinal cord process the information and send commands directly to motor neurons that control muscles in your arm and hand. Your muscles contract and you quickly withdraw your hand. Meanwhile, messages of pain travel to the brain. Shortly after your arm moves, you feel pain.

Peripheral Nervous System The peripheral nervous system includes the network of nerves that links the rest of your body to your brain and spinal cord. The peripheral nervous system carries information to the central nervous system, and then carries responses from the central nervous system to the rest of the body.

Sensory Division Some nerves in the sensory division carry information about your outside environment from your ears, eyes, and other sense organs. Other sensory nerves carry information about internal body conditions such as blood pressure and heart rate.

Motor Division Somatic Nervous System Motor nerves in the somatic nervous system carry signals that control voluntary actions. Autonomic Nervous System Motor nerves in the autonomic nervous system regulate actions that happen automatically.

1 1) Brain 2 2) Spinal cord 3) Peripheral nerves 3

Active Art: The Nervous System Click on the screen above to launch the Active Art.

Keeping Healthy Rest, good nutrition, and daily exercise can help keep your nervous system functioning properly. The most important step you can take to care for your nervous system is to protect it from injury.

Avoiding Head Injuries A bruiselike injury to the brain is known as a concussion. A coma is a prolonged period of deep unconsciousness. Head injuries can be avoided. Wear a helmet when you play contact sports. Fasten your seat belt. Before diving into water be sure that it is deep enough and that there are no underwater hazards. Avoid drugs and alcohol.

Avoiding Spinal Cord Injuries Paralysis is the loss of the ability to move and feel some part of the body. Spinal cord injuries can be avoided Fasten your seat belt. Take care when diving. Avoid drugs and alcohol.

Avoiding Nerve Injuries Individual peripheral nerves also can be injured. To help prevent carpal tunnel syndrome and similar nerve injuries, it is important to take breaks from repetitive motions and to maintain good posture.

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Preventing Infections Nervous system infections are rare because its tissues are well protected. Meningitis (men in JY tis) causes inflammation of the membranes surrounding the brain and spinal cord. The most serious form of meningitis can be prevented with a vaccine. A bite from an infected animal can transmit rabies, an infection of the central nervous system. Avoid contact with animals that act sick or behave strangely.

Living with Epilepsy Sudden, uncontrolled nerve impulses in the brain can lead to a seizure. People with a disorder called epilepsy are prone to seizures. Epileptic seizures include facial twitching, loss of awareness, and muscle spasms.

Preventing Headaches The most common problem of the nervous system that people experience are headaches. Proper diet, exercise, and sleep can help prevent headaches. If you can identify certain foods or odors that trigger headaches, you may be able to avoid those triggers.

Vocabulary neuron The basic unit of the nervous system that carries nerve impulses. cerebrum A part of the brain that contains several specialized regions that receive messages from sense organs, and control movement, memory, communication, and reasoning. cerebellum A part of the brain that coordinates movements and balance. brain stem The area of the brain between the cerebellum and the spinal cord; it controls automatic functions such as heartbeat and blood pressure.

Vocabulary spinal cord A thick column of nerve tissue in the central nervous system that links the brain to most of the nerves in the peripheral nervous system. reflex An automatic response of the nervous system to the environment. concussion A bruiselike injury to the brain caused by brain tissue hitting the skull during a collision. coma A prolonged period of deep unconsciousness. paralysis The loss of the ability to move and feel some part of the body.

Vocabulary meningitis An infection that causes inflammation of the membranes surrounding the brain and spinal cord. seizure An episode of erratic nerve impulses in the brain that may lead to loss of consciousness, muscle spasms, and other uncontrollable symptoms. epilepsy A condition in which a person is prone to seizures.

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End of Section 11.3 Click on this slide to end this presentation.