Table of Contents Chapter Preview 15.1 How the Nervous System Works 15.2 Divisions of the Nervous System 15.3 Sight and Hearing 15.4 Smell, Taste, and Touch 15.5 Alcohol and Other Drugs • 15.1 How the Nervous System Works • 15.2 Divisions of the Nervous System • 15.3 Sight and Hearing • 15.4 Smell, Taste, and Touch • 15.5 Alcohol and Other Drugs

Chapter Preview Questions • 1. Which part of the skeletal system protects the brain? • a. spine • b. pelvis • c. skull • d. joint

Chapter Preview Questions • 2. Which muscles can you control voluntarily? • a. heart muscles • b. leg muscles • c. diaphragm • d. stomach muscles

Chapter Preview Questions • 3. What is the smallest unit of any body system? • a. structure • b. organ • c. tissue • d. cell

Chapter Preview Questions • 4. What is the eye designed to receive from the environment? • a. light rays • b. vibrations • c. lenses • d. motion

You smell a delicious aroma. You walk into the kitchen and see a bag of popcorn in the microwave. You hear some kernels still popping. Then you think to yourself, “Snack time!” Which body systems enabled you to smell, walk, see, hear, and think? How did each system play a part in your response? How do organs and other structures enable the nervous system to function?

Suffixes Pollutant Something that pollutes or makes dirty -ant A person or thing that

Suffixes Criticism Action of judging the value of something -ism Action or practice of

Suffixes Sickness Condition of being sick -ness Condition of; state of

Suffixes -ous Having; full of Disastrous Full of disaster

Apply It! 1. What is the suffix in the word nearsightedness? What does the suffix mean? -ness; it means the condition of being nearsighted 2. The word stimulate means “to increase activity. ” Predict the meaning of stimulant. Revise your definition as needed after you read Section 5. Sample answer: It means something that increases activity. Revised definition: A stimulant is a drug that speeds up body processes.

End of Chapter Preview

Section 1: How the Nervous System Works • What are the functions of the nervous system? • What is the structure of a neuron and what kinds of neurons are found in the body? • How do nerve impulses travel from one neuron to another?

The Neuron • A neuron has a large cell body that contains the nucleus, threadlike extensions called dendrites, and an axon.

How a Nerve Impulse Travels • For a nerve impulse to be carried along at a synapse, it must cross the gap between the axon and the next structure. The axon tips release chemicals that carry the impulse across the gap.

More on Nerve Impulses • Click the PHSchool.com button for an activityabout nerve impulses.

Nervous System • Click the Video button to watch a movie aboutthe nervous system.

End of Section: How the Nervous System Works

Section 2: Divisions of the Nervous System • What are the structures and functions of the central nervous system? • What are the structures and functions of the peripheral nervous system? • What is a reflex? • What are two ways in which the nervous system can be injured?

Central Nervous System • The central nervous system is the control center of the body. It includes the brain and spinal cord.

Nervous System Activity • Click the Active Art button to open a browser window and access Active Art about nervous system.

The Brain • There are three main regions of the brain that receive and process information. These are the cerebrum, the cerebellum, and the brain stem.

Peripheral Nervous System • The peripheral nervous system consists of a network of nerves that branch out from the central nervous system and connect it to the rest of the body. The peripheral nervous system is involved in both involuntary and voluntary actions.

Reflexes • A reflex is an automatic response that occurs very rapidly and without conscious control.

End of Section: Divisions of the Nervous System

Section 3: Sight and Hearing • How do your eyes enable you to see? • How do you hear and maintain your sense of balance?

Vision • You eyes respond to the stimulus of light. They convert that stimulus into impulses that your brain interprets, enabling you to see.

Virtual Dissection of the Eye Activity • Click the Active Art button to open a browser window and access Active Art about a virtual dissection of the eye.

Vision • Light coming from an object enters your eye and is focused by the lens. The light produces an upside-down image on your retina. Receptors in your retina then send impulses to your cerebrum, which turns the image right-side up.

Hearing and Balance • Your ears are the sense organs that respond to the stimulus of sound. Ears convert the sound to nerve impulses that your brain interprets.

Sound Intensity • Sound intensity, or loudness, is measured in units called decibels. The threshold of hearing for the human ear is 0 decibels. For every 10-decibel increase, the sound intensity increases ten times. Thus, a 20-decibel sound is ten times more intense than a 10-decibel sound. A 30-decibel sound is 100 times more intense than a 10-decibel sound. Sound levels for several sound sources are shown in the bar graph.

Decibels, or sound level; type of sound Reading Graphs: What unit of measure is represented on the y-axis? What is represented on the x-axis? Sound Intensity

20dB; 60dB; 120dB Interpreting Data: What is the sound intensity in decibels of a whisper? Normal talking? A rock concert? Sound Intensity

20 dB vs. 60 dB, which is 10,000 times more intense Calculating: How much more intense is normal talking than a whisper? Explain. Sound Intensity

Rock concert; jet plane taking off Predicting: Based on the graph, what types of sound could be painful if you were exposed to them? Sound Intensity

End of Section: Sight and Hearing

Section 4: Smell, Taste, and Touch • What are the functions of the nervous system? • What is the structure of a neuron and what kinds of neurons are found in the body? • How do nerve impulses travel from one neuron to another?.

Smell and Taste • The senses of smell and taste work closely together. Both depend on chemicals in food or in the air. The chemicals trigger responses in receptors in the nose and mouth.

Links on the Senses • Click the SciLinks button for links on the senses

End of Section: Smell, Taste, and Touch

Section 5: Alcohol and Other Drugs • What are the functions of the nervous system? • What is the structure of a neuron and what kinds of neurons are found in the body? • How do nerve impulses travel from one neuron to another?

Drug Abuse • Drug abuse can have serious consequences. However, there are ways to tell if someone is abusing drugs and ways to help that person.

Alcohol • Alcohol is a drug found in many beverages, including beer, wine, cocktails, and hard liquor. Alcohol is a powerful depressant and affects every system of the body.

Links on Drug Addiction • Click the SciLinks button for links on drug addiction.

End of Section: Alcohol and Other Drugs

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