Focus on California Life Science 7th Grade Unit 4 - Chapter 15 Nervous System

Chapter The Nervous System ( Preview , The anatomy and physiology of plants and animals illustrate the complementary nature of ture and function . As a basis for understanding this concept . Students know organ systems function because of the of individual organs , tissues , and cells . The failure of can affect the entire system . Students Know how to relate the structures of the eye and ear to their functions , Physical principles underlie biological structures and functions . As a basis for understanding this concept . Students know that for an object to be seen , light emitted by or scattered from it must be detected by the eye . Scientific progress is made by asking meaningful questions and conducting careful tions . As a basis for understanding this concept and addressing the content in the other three strands , students should develop their own questions and perform . Students will , Communicate the logical ' among hypotheses , science concepts , tests ' i ducted , data collected , and ' conclusions drawn from ' i scientific evidence . Without your nervous system , a sport like would be impossible ! Ell ,

' The Nervous System Focus on the BIG Idea How do organs and other structures enable the nervous system to function ?

Check What You Know 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 ?

Chapter 15 595 The images shown here represent some of the Key Terms in this chapter . You can use this vocabulary skill to help you understand the meaning of some key terms in this chapter . A suffix is a word part that is added to the end of a word to change its meaning . For example , the suffix means state of . When this suffix is added to the adjective dark , it forms the noun darkness . Darkness means the state of being dark . The table below lists some common and explains their meanings , The table also gives you an example that uses the suffix . You can use the meanings of these to help understand the meanings of some key terms . Meaning of Suffix I Example and Meaning of Example Pollutant Something that pollutes or makes dirty . Alcohol is a drug found in certain beverages . Predict the meaning of alcoholism . Revise your definition as needed after you read Section . The word stimulate means to . It needed after you read Section . neuron

Chapter Vocabulary Section ( page 500 ) stimulus nerve neuron neuron dendrite motor neuron Section page 606 ) brain brain stem spinal cord reflex cerebrum concussion cerebellum central nervous system peripheral nervous system somatic nervous system autonomic nervous system ( page 611 . cornea optic nerve ' pupil eardrum iris hammer central nervous system i , am , taste retina stirrup rods cochlea cones semicircular canal Section ( page 521 ) semicircular canals , Section ( Page 624 ) drug withdrawal drug abuse depressant tolerance stimulant addiction alcoholism ' eardrum I ' Build Science Vocabulary Online Visit Web Code ' Chapter 15 597

Identify Main Ideas The main idea in a paragraph or section is the most important idea . Headings and the boldface key concept statements can often help you identify main ideas . The details in a paragraph or section support the main idea . Details are usually specific facts and examples that help readers understand the main idea . Look for the main idea and details in the paragraph below . Then copy the graphic organizer in your notebook and complete it . Depressants Depressants are drugs that slow down the activity of the central nervous system . When ple take depressants , their muscles relax and they may feel sleepy . They may fail to respond normally . For example . depressants may prevent people from responding quickly to the danger of an onrushing car . Detail Detail Muscles relax Become sleepy Apply It ! What is the heading of the paragraph ?

What does it tell you about the main idea ?

Choose one detail . Explain how it supports the main idea . In this chapter , look for the main ideas in paragraphs . Also try to identify the main ideas for the text following each heading .

standards Investigation Is Sense and Nonsense An optical illusion is a picture or other visual effect that tricks you into seeing something incorrectly . In this investigation , discover how your senses sometimes can be fooled by illusions . Your Goal To demonstrate how different people respond to illusions To complete this investigation you must try out a variety of optical illusions as well as some illusions that involve the senses of hearing or touch select one or more illusions and set up an experiment to monitor people responses to the illusions learn why the illusions fool the senses follow the safety guidelines in Appendix A Plan It ! In a small group , discuss illusions that you know about . Look in books to learn about others . Which illusions would make an interesting experiment ?

How could you set up such an experiment at a science fair ?

Find out how your nervous system allows you to sense your environment . For example , which structures are involved in observing the optical illusion below ?

Use this chapter and other print or electronic resources to learn how these structures function when people are fooled by illusions . Stare for 30 seconds at the red dot in the center of the flag . Then stare at the dot in the white box for a few seconds . Did you see an illusion ?

15 599 Section How System Works Standards Focus Students know organ systems function because of the contributions of individual organs . tissues , and cells . The failure of any part can affect the entire system . nervous system ?

What are the functions of the What is the structure of a neuron and what kinds of neurons are found in the body ?

How do nerve impulses travel ' neuron 30 another ?

Key Terms stimulus response I neuron nerve impulse dendrite axon nerve sensory neuron motor neuron synapse 6000 May Systems Work Together ?

Trace the outline of a penny in twelve diflerent places on a piece of paper . Number the circles through 12 . Write the numbers randomly , in no particular order . Now , pick up the penny again . Put it in each circle , one after another . in numerical order , starting at and ending at 12 . Think It Over inferring Make a list of all the sense organs , muscle movements , and thought processes used in this activity . Compare your list with your classmates lists . Which organ systems were working together ?

What organ system coordinated all the different processes involved in this task ?

The ball whizzes toward the soccer goalie She for the ball , and in one swift movement blocks it from entering the net . To tend goal , soccer players need excellent coordination and keen vision . In addition . they must remember what they have learned from years of practice . Whether or not you play soccer , you too need coordination , memory , and the ability to learn . Your nervous system carries out all these functions . The nervous system includes the brain . spinal cord , and nerves that run throughout the body . It also includes sense organs such as the eyes and ears . Functions of the Nervous System The Internet lets people gather information from anywhere in the world with the click of a button . Like the Internet , your nervous system is a communications network . But it is much more efficient than the Internet . The nervous system receives information about what is happening both inside and outside your body . It also directs the way in which your body responds to this information . In addition , your nervous system helps maintain homeostasis . Without your nervous system , you could not move , think . feel pain , or taste a spicy taco .

Receiving Information Because of your nervous system , you are aware of what is happening in the environment around you . For example , you know that a fly is buzzing around your head , that the wind is blowing , or that a friend is telling a funny joke . Your nervous system also checks conditions inside your body , such as the level of your blood pressure . Responding to Information Any change or signal in the environment that can make an organism react is called a stimulus ( yoo ) plural stimuli ) A buzzing is a stimulus . After your nervous system analyzes the stimulus . it causes a response . A response is what your body does in tion to a swat at the . Some nervous system responses , such as swatting a , are voluntary , or under your control . However , many processes necessary for life , such as the beating of your heart , are trolled by involuntary actions of the nervous system . Maintaining Homeostasis The nervous system helps maintain homeostasis by directing the body to respond to the information it receives . For example , when you need energy , your nervous system prompts you to feel hungry and then eat . This action maintains homeostasis by supplying your body with the nutrients and energy it needs . Av , What is a stimulus ?

The eyes receive information that a soccer ball is zooming toward her . energy needs the game . FIGURE The Nervous System at Work The zooming soccer ball is a stimulus . The goalie responds by lunging toward the ball and blocking the shot . interpreting Diagrams How does the goalie nervous maintain homeostasis ?

system help her body Flour Structure of a Neuron A neuron has one axon and many dendrites that extend from the cell body . Go sateen For More on nerve impulses Visit Web Code The Neuron Your nervous system various organs , tissues . and cells For example , your brain is an organ , and the nerves running out your body are tissues . The cells that tarry information through your nervous system are called neurons ( or nerve . The Structure of a Neuron The structure of a neuron it to carry nerve impulses . A neuron has a large cell body that contains the nucleus , extensions called dendrites , and an axon . The dendrites carry impulses toward the cell body . The axon carries impulses away from the cell body . Find the dendrites and axon in Figure . Nerve impulses begin in a dendrite , next move toward the cell body , and then move down the axon . A neuron can have many dendrites , but it has only one axon . An axon , however , can have more than one tip , so the impulse can go to more than one other cell . Axons and dendrites are sometimes called nerve . Nerve fibers are often arranged in parallel bundles covered with tissue , something like a package of uncooked spaghetti wrapped in cellophane . A bundle of nerve is called a nerve . kinds in the neurons , and motor neurons . Figure shows how these three kinds of neurons work together . A sensory neuron up stimuli from the internal or nal environment and converts each stimulus into a nerve impulse . The impulse travels along the sensory neuron until it reaches an , usually in the brain or spinal cord . An is a neuron that carries nerve impulses from one neuron to another . Some pass impulses from sensory rons to motor neurons . A motor neuron sends an impulse to a muscle or gland , and the muscle or gland reacts in response . What is the function or an axon ?

How a Nerve Impulse Travels Every day of your life , billions of nerve impulses travel through your nervous system . Each of those nerve impulses begins in the dendrites of a neuron . The impulse moves rapidly toward the neurons cell body and then down the axon until it reaches the axon tip . A nerve impulse travels along the neuron in the form of electrical and chemical signals . Nerve impulses can travel as fast as 120 meters per second !

FIGURE The Path of a Nerve Impulse When you hear your phone ring , you pick it up to answer it . Many sensory neurons , and motor neurons are involved in this action . Interpreting Diagrams To where does the impulse pass from the sensory neurons ?

Muscle in hand Receptors in ear Sensory Neuron Nerve impulses begin when receptors pick up stimuli from the environment . Receptors in the ear pick up the sound of the phone ringing . The receptors trigger nerve impulses in sensory neurons . From the sensory neurons , the nerve impulse passes to in the brain . Your brain interprets the impulses from many and makes you realize that the phone is ringing . Your brain also decides that you should answer the phone . Motor Neuron Impulses then travel along thousands of motor neurons . The motor neurons send the impulses to muscles . The muscles carry out the response , and you reach for the phone . Chapter 15 603

Axon tip Dendrite Axon tip Dendrite Chemical carrying more impulse The Synapse When a nerve impulse reaches the tip of an axon , chemicals are released into the gap at the synapse . The chemicals carry the nerve impulse across the gap . The Synapse What happens when a nerve impulse reaches the axon tip at the end of a neuron ?

At that point , the impulse can pass to the next structure . Sometimes the structure is the dendrite of another neuron . Other times , the structure is a muscle or a cell in another organ , such as a sweat gland . The junction where one neuron can transfer an impulse to another structure is called a synapse ( SIN aps ) How an Impulse Transferred Figure shows a synapse between the axon tip of one neuron and the dendrite of another neuron . Notice that a small gap these two structures . 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 . You can think of the gap at a synapse as a river , and an axon as a road that leads up to the riverbank . The nerve impulse is like a car traveling on the road . To get to the other side , the car has to cross the river . The car gets on a ferry boat , which carries it across the river . The chemicals that the axon tips release are like the ferry , carrying the nerve impulse across the gap . Reading Target Reading Skill Identify Main Ideas Reread the text following the heading Functions of the Nervous System ( pages ) Note that the Key Concept is the main idea . List three details that support this main idea Reviewing Key Concepts a . Listing What are three functions of the nervous system ?

Describing Give an example of a stimulus and describe how the nervous system produces a response . Predicting Your heart rate is controlled by involuntary actions of the nervous system . What would life be like if your heartbeat were under voluntary control ?

Identifying Identify the three kinds of neurons that are found in the nervous system . Explaining do the three kinds of neurons interact to carry nerve impulses ?

5040 Comparing and Contrasting How do sensory neurons and motor neurons differ ?

a . Reviewing What is a synapse ?

Sequencing Outline the steps by which a nerve impulse reaches and then crosses the gap at a synapse . Activity Pass the Salt , Please During dinner , ask a family member to pass the salt to you . Observe what your family member then does . Explain that the words you spoke were a stimulus and that the family reaction was a response . Describe which structures of the nervous system detect stimuli and enable a response .

Ready or Not ! Problem Do people reaction times vary at different times of the day ?

Skills Focus developing hypotheses , controlling variables , drawing conclusions Material meter stick Procedure PART Observing a Response to a Stimulus . Have your partner hold a meter stick with the zero end about 50 above a table . Get ready to catch the meter stick by positioning the top of your thumb and finger just at the zero position , as shown in the photograph . Your partner should drop the meter stick without any warning . Using your thumb and forefinger only ( no other part of your hand ) catch the meter stick as soon as you can . Record the distance in centimeters that the meter stick fell . This distance is a measure of your reaction time . Designing Your Experiment . With your partner , discuss how you can use the activity from Part to find out whether people reaction times vary at different times of day . Consider the questions below . Then , write up your experimental plan . hypothesis will you test ?

What variables do you need to control ?

How many people will you test ?

How many times will you test each person ?

Submit your plan for your teacher review . Make any changes your teacher mends . Create a data table to record your results . Then , perform your experiment . Analyze and conclude . Inferring In this lab , what is the stimulus ?

What is the response ?

Is the response or involuntary ?

Explain . Drawing Conclusions Which body systems were involved in people reactions ?

Developing Hypotheses What hypothesis did you test in Part ?

Controlling Variables In Part , why was it important to control all variables except the time of day ?

Drawing Conclusions Based on your results in Part , do people reaction times vary at different times of the day ?

Explain . Communicating Write a paragraph to explain why you can use the distance on the meter stick as a measure of reaction time . More to Explore Do you think people can do arithmetic problems more quickly and accurately at certain times of the day ?

Design an experiment to investigate this question . Obtain your teachers permission before carrying out your investigation . Chapter 15 605 000 Standards Focus Students know organ systems function because of the contributions of individual organs . tissues , and cells . The failure of any part can affect the entire 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 ?

Key central nervous system ' peripheral nervous system brain a spinal corn cerebrum cerebellum brain stem somatic nervous system autonomic nervous system reflex concussion The traffic cop keeps everybody moving . 6060 Divisions of the Nervous System . Standards How Does Your Knee React ?

Sit on a table or counter so that your legs dangle freely . Make sure that your partner is not directly in front of your legs . Have your partner use the side of his or her hand to tap one of your knees gently just below the kneecap . Observe what happens to your leg . Note whether you have any control over your reaction . Change places with your partner . Repeat Steps and . Think It Over Inferring When might it be an advantage for your body to react very quickly and without your conscious control ?

You are standing at a busy street corner , waiting to cross the street . A cop blows his whistle and waves his arms . For the heavy to move smoothly . there needs to be a cop and responsive drivers . The cop nates the movements of the drivers . and they steer the cars safely through the intersection . Similarly . your nervous system has two divisions that work together . The central nervous system consists of the brain and spinal cord . The peripheral nervous system ( puh uh rul ) includes all the nerves located outside of the central nervous system . The central nervous system is like a traffic cop . The peripheral nervous system is like the drivers and pedestrians .

Central Nervous System You can see the central and peripheral nervous systems in Figure . The central nervous system is the control center of the body . It includes the brain and spinal cord . All mation about what is happening in the world inside or outside your body is brought to the central nervous system . The brain , located in the skull , is the part of the central nervous tem that controls most functions in the body The spinal cord is the thick column of nervous tissue that links the brain to most of the nerves in the peripheral nervous system . Most impulses from the peripheral nervous system travel through the spinal cord to get to the brain . Your brain then directs a response . The response usually travels from the brain , through the spinal cord , and then to the peripheral nervous system . For example , here is what happens when you reach under the sofa to a lost quarter . Your move over the , searching for the quarter . When your touch the quarter , the stimulus of the touch triggers nerve impulses in sensory neurons in your gers . These impulses travel through nerves of the peripheral nervous system to your spinal cord . Then the impulses race up to your brain . Your brain interprets the impulses , telling you that you found the quarter . Your brain starts nerve impulses that move down the spinal cord . From the spinal cord . the impulses travel through motor neurons in your arm and hand . The impulses in the motor neurons cause your to grasp the quarter . What are the parts of the central 03 nervous system ?

The Nervous System The central nervous system consists of the brain and spinal cord . The peripheral nervous system includes all the nerves that branch out from the brain and spinal cord . Go For Nervous System activity Visit Web Code Peripheral nerves Chapter 15 607

Controlling Variables Are people better able to memorize a list of words in a quiet room or in a room where soft music is playing ?

Write a hypothesis that addresses this question . Design an experiment to test your hypothesis . Make sure that all variables are controlled except the one you are versus quiet . Check your procedure with your teacher Then form your experiment . Did your results support your hypothesis ?

NO The Brain and Spinal Cord Your brain contains about 100 billion neurons , all of which are . Each of those neurons may receive messages from up to other neurons and may send messages to about ( more ! Three layers of connective tissue cover the brain . The space between the middle layer and innermost layer is with a watery . The skull , the layers of connective tissue , and the all help protect the brain from injury . There are three main regions of the brain that receive and process information . These are the cerebrum , in Figure . Cerebrum The largest part of the brain is called the brum . The ( suh brum ) interprets input from the senses , controls movement , and carries out complex tal processes such as learning and remembering . Because of your cerebrum , you can locate your favorite comic strip in the newspaper , read it , and laugh at its funny characters . The is divided into a right and a left half . The right half sends impulses to skeletal muscles on the left side of the body . In contrast , the left the right side of the body . When you reach with your right hand for a pencil , the messages that tell you to do so come from the left half of the . in addition , each half of the cerebrum slightly different kinds of mental activity . The right usually associated with creativity and artistic ability . The left half is usually associated with mathematical skills , language , and logical thinking . As you can see in Figure , certain areas of the are associated with smell , touch , taste , hearing , and vision . Other areas control movement , speech , written language , and abstract thought . Different tissues in the cerebrum carry out different functions . cerebellum and Brain Stem The second largest part of your brain is the cerebellum . The cerebellum ( sehr uh BEL um ) coordinates muscle action and balance . When you walk , the impulses that move your feet start in your cerebrum . However , your cerebellum gives you the muscular coordination and sense of balance that keep you from falling down . The brain stem , which lies beneath the cerebrum and , controls your involuntary that occur automatically . For example , neurons in the brain stem regulate your breathing and help control your heartbeat . What the brain stem control ?

The Brain of the three main parts of the cerebrum , cerebellum , and brain out more than ' one specific function . I The cerebrum is the largest Interpreting Diagrams What are 37935 of the cerebrum control such functions as movement . the senses , speech , and abstract thought . three functions of the cerebrum ?

A The cerebellum coordinates the actions of muscles and helps maintain balance . The brain stem controls involuntary actions such as breathing and ' heart rate . Top View of Cerebrum cerebrum is associated logical thinking . artistic ability .

610 The Spinal Cord The spinal cord is the link between your brain and the peripheral nervous system . Run your down the center of your back to feel the bones of the vertebral column . The vertebral column surrounds and the spinal cord . The layers of connective tissue that round and protect the brain also cover the spinal cord . Like the brain , the spinal cord is further protected by a watery . Peripheral Nervous System The second division of the nervous system is the 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 . A total of 43 pairs of nerves make up the peripheral vous system . Twelve pairs originate in the brain . The other 31 spinal in the spinal cord . One nerve in each pair goes to the left side of the body , and the other goes to the right . As you can see in Figure , spinal nerves leave the spinal cord through spaces between the vertebrae . How Spinal Nerves Function A spinal nerve is like a lane highway . Impulses travel on a spinal nerve in two to and from the central nervous system . Each spinal nerve contains axons of both sensory and motor neurons . The sensory neurons carry impulses from the body to the central nervous system . The motor neurons carry impulses in the site the central nervous system to the body . Spin Cord Spinal nerve FIGURE The Spinal Nerves The spinal nerves , which connect to the spinal cord , emerge from spaces between the vertebrae . Each spinal nerve consists of both sensory and motor neurons . Spinal disk

FIGURE Somatic and Autonomic Nervous Systems The somatic nervous system controls voluntary actions . The autonomic nervous system controls actions . Classifying Which system helps the artist heartbeat ?

Actions Controlled by the Somatic Nervous System Hands shape the clay . Foot turns the wheel . Mouth smiles . Actions Controlled by the Autonomic Nervous System Heartbeat is regulated . Breathing rate is kept steady . Body temperature remains constant . Somatic and Autonomic Systems The nerves of the peripheral nervous system can be divided into two groups , the somatic ( soh MAT ik ) and autonomic ( uh ik ) nervous systems . The nerves of the somatic nervous system control voluntary actions such as using a fork or tying your shoes . in contrast , nerves of the autonomic nervous system control involuntary actions . For example , the autonomic vous regulates the contractions of the smooth muscles that adjust the diameter of blood vessels . Heading What kinds of actions are controlled by the ' autonomic nervous system ?

Reflexes Imagine that you are watching an adventure movie . The movie is so thrilling that you don notice a circling above your head . When the fly zooms right in front of your eyes , however . your eyelids immediately blink shut . You didn decide to close your eyes . The blink , which is a , is a response that happened automatically . A is an automatic response that occurs very rapidly and without conscious control . help to protect the body . if you did the Standards on page 606 , you observed another . You Blinked ! Can you make yourself not blink ?

Find out in this activity . Put on safety goggles . Have your partner stand across from you and gently toss ten cotton balls , one at a time , toward your goggles . Your partner should not give you any warning before a toss . Count the number of times you blink and the number of times you do blink . Interpreting Data Compare the two numbers . Why is blinking considered a reflex ?

What structure protects your eye when you blink ?

611 A Reflex Pathway As you have learned . the contraction of skeletal muscles is usually controlled by the brain . However , in some actions . skeletal muscles contract with the ment of the spinal cord the brain . Figure shows the action that occurs when you touch a sharp object . When your finger touches the object , sensory neurons send impulses to the spinal cord . The impulses may then pass to in the spinal cord . from there the impulses pass directly to motor neurons in your arm and hand . The muscles then contract , and your hand jerks up and away from the sharp object . By removing your hand quickly , this protects you from getting badly cut . Signaling the Brain At the same time that some nerve impulses make your arm muscles contract , other nerve impulses travel up your spinal cord to your brain . When these impulses reach your brain , your brain interprets them . You then feel a sharp pain in your . It takes longer for the pain impulses to get to the brain and be interpreted than it does for the action to occur . By the time you feel the pain , you have already moved your hand away . What is an example of a reflex ?

A Reflex Action If you touch a sharp object , your hand immediately jerks away . This action , which is known as a reflex , happens automatically . Follow the numbered steps to understand how a reflex happens . Sequencing Do you pull your hand away before or after you feel the pain ?

Explain . neurons in your fingertip detect a pain stimulus . Nerve impulses travel to your spinal cord . Nerve impulses return to motor neurons In your hand . and you pull your hand away . you pull your hand away . nerve impulses travel to your brain . You feel the pain .

Nervous System Injuries The nervous system can suffer injuries that interfere with its functioning . Concussions and spinal cord injuries are two ways in which the central nervous system can be damaged . concussions A concussion is a injury of the brain . A concussion occurs when the soft tissue of the brain collides against the skull . Concussions can happen when you bump your head in a hard fall , in an automobile crash , or during a contact sport such as football . With most concussions , you may have a headache for a short time , but the injured tissue heals by itself . However , with more serious concussions , you may lose consciousness , ence confusion . or feel drowsy after the injury . To decrease your chances of getting a brain injury , wear a helmet during activities in which you risk bumping your head . FIGURE 10 Protecting the Nervous System You can help Spinal Cord Injuries spinal cord injuries occur when the cord wearing a spinal cord is cut or crushed . As a result , axons in the injured seatbelt when you travel in a car . region are damaged , so they fail to carry impulses . This type of injury usually results in paralysis , which is the loss of ment in some part of the body . Car crashes are the most common cause of spinal cord injuries . i What is paralysis ?

Reading Section Assessment Vocabulary Skill In the term nervous a . Defining What is a ?

system . the word nervous contains the suffix . Sequencing Trace the pathway of a reflex in What does this suffix mean ?

How does it relate to the nervous system , the meaning Of ' inferring How do reflexes help protect the Reviewing Key Concepts mil 50 ?

a . Reviewing What is a concussion ?

Applying Concepts How can you reduce your risk of concussion ?

a . Listing What two structures are part of the central nervous system ?

Describing Describe the functions of the three main regions of the brain . Relating Cause and Effect What symptoms ' might indicate that a person cerebellum In I Ce has been injured ?

I In . Identifying What are the two groups of you nerves into . which the peripheral nervous of the aft and haw of ! Sim ?

of mental . Comparing and Contrasting How do the half , as we as which we aft , body functions of the two groups of peripheral nerves differ ?

Chapter 15 Section Integrating Physical Science Sight and Hearing ' Students know how to can You See Everything with One Eye ?

relate the structures of the eye and . Write an and an on a sheet of paper . The should be ear to their functions . Students know that for an about to the of the object to be seen , right emitted by . Hold the sheet of paper at arm length . from it must be . Close or cover your left eye . Stare at the with your right eye . ed by he eye . Slowly move the paper toward your face while staring at the . How do your eyes enable you what do you , to my . Repeat the activity , keeping both eyes open . What difference How do you hear and maintain do you once ?

your sense of balance ?

Think it Ovef es Posing Questions Write two questions about vision that you Key Terms could investigate using the and the . cornea pupil I iris lens retina rods ' cones optic nerve eardrum hammer The pitcher goes into her windup , keeping her eye on the strike anvil stirrup cochlea zone . The batter watches the pitcher release the ball and then ' i i ' a swings . Crack ! She drops the bat and sprints toward first base . From your seat , you watch the ball travel toward the . Will it be a base hit ?

The left watches the ball speed toward her . over her head for a double ! Players and spectators alike followed the first rule of baseball Keep your eye on the ball . As the ball moves near and far , your eyes must adjust continuously to keep it in focus . Fortunately , this change in focus happens automatically . Hold I It The Nervous System Keep your eye on the 614

Vision Your eyes are the sense organs that enable you to see the objects in your environment . Your eyes respond to the stimulus of light . They convert that stimulus into impulses that your brain interprets , enabling you to see . How Light Enters Your Eye Light rays from an object enter the eye through the structures shown in Figure 11 . First , the light strikes the cornea ( nee uh ) the clear tissue that covers the front of the eye . The light then passes through a chamber behind the cornea and reaches the pupil . The pupil is the opening through which light enters the eye . You may have noticed that pupils change size when they go from a dark room into bright sunshine . In bright light , the pupil becomes smaller . In dim light , the pupil becomes larger . The size of the pupil is adjusted by muscles in the iris . The iris is a circular structure that surrounds the pupil and regulates the amount of light entering the eye . Together , the iris and the pupil act much like the aperture of a camera . The iris also gives the eye its color . What is the function of the iris ?

FIGURE 11 The Eye The eye is a complex organ that senses light . Interpreting Diagrams What structure adjusts the size of the pupil ?

Pupil in Bright Light ?

For Visit Web Code chapter 15 515 Muscles Seeing Seeing Far Away Close Up The muscles The muscles relax . making contract . the lens thin . making the ' Discover straw Try to inferring 616 Working Together work together . With your arms fully extended , hold a drinking pipe cleaner in the other . With both eyes open , try to insert the pipe cleaner into the straw . Now close your right eye . cleaner into the straw . Repeat Step with your left eye closed . lens thick . Activity how your two eyes in one hand and a insert the pipe How does closing one eye affect your ability to judge distances ?

Focusing the Lens Muscles change the shape of the lens . allowing the eye to focus on objects at different distances . Applying Concepts What structures does light pass through before it reaches the lens ?

Light Is Focused Light rays enter the eye through the cornea . The cornea the diverging rays that come from an object into converging rays . Then the light passes through the pupil and strikes the lens . The lens is a structure that focuses light . The lens of your eye functions something like the lens of a camera . Because of the way in which the lens of the eye bends the light rays , the image it produces is upside down and reversed . Muscles that attach to the lens adjust its shape , producing an image that is in focus . How You See an Image After passing through the lens , the focused light rays pass through a transparent , jellylike . Then the rays strike the ( uh ) a sheet of sensitive cells that lines the back of the eye . The retina , which has the same job as a or video chip in a camera , contains about 130 million receptor cells . These cells respond to light . There are two types of receptors rods and cones . work best in dim light and enable you to see black , white , and shades of gray . In contrast , work best in bright light and enable you to see colors . This difference between rods and cones explains why you see colors best in bright light , but you see only shadowy gray images in dim light . The rods and cones send electrical impulses to the brain through a short , thick nerve called the . One optic nerve comes from the left eye and the other one comes from the right eye . The brain interprets the signals . First , it turns the reversed image up . Then the brain combines the images from each eye . You see a single image . Seeing in Depth Unlike many animals , humans have both eyes in the front of the head . Both your eyes look ward . However , you see a slightly different image with your right eye than you do with your left eye . Your brain pares the images from your two eyes . This comparison gives you vision . That is , you can judge how close or how far away an object is . What enables humans to see in dimensions ?

FIGURE 13 How You See Light coming from an object enters your eye and is focused by the cornea and lens . An upside down image forms on your retina . Receptors in your retina then send impulses to your cerebrum , which turns the image up . Comparing and Contrasting Which receptors work best in dim light ?

Object Rods and Cones Receptors in the retina include rods ( shown in green ) and cones ( shown in blue ) forms An image is focused on the retina . Notice that the image is upside down . I on the retina Chapter 15 Hearing and Balance Have you ever watched a dog listen for its owners voice ?

Dogs and other mammals have muscles that enable their external ears to move . This movement helps the animals detect faint sounds and identify where the sounds come from . Though your ears don move like those of a dog , they do detect sound . Your ears are the sense organs that respond to the of sound . The ears convert sound to nerve impulses that your brain interprets . So when you hear an alarm clock , your brain tells you that it time to wake up . How Sound Produced Sound is produced by vibrations that travel as waves . The material that is vibrating , or moving rapidly back and forth , may be almost guitar string , an insect wings , or a stereo speaker . The vibrations , or sound waves , move outward from the Sensing Sound . A dog can cock its enema , ear source of the sound , something like ripples moving out from a when listening to sound stone dropped in water . The sound waves cause particles , such as the gas molecules that make up air , to vibrate . In this way , sound is carried . When you hear a friends voice , for example , sound waves have traveled from your friend larynx to your ears . Sound waves can also travel through liquids , such as water , and solids , such as wood . FIGURE 14 Math Number Sense A Data Il ' il Sound Levels Sound Intensity Sound intensity , or loudness , is measured in units called decibels . The threshold of hearing for the human ear is decibels . For every increase , the sound intensity increases ten times . Thus , a sound is ten times more intense than a sound , not twice as intense . A sound is 100 times more intense than a sound . Sound levels for several sound sources are shown in the bar graph . Interpreting Data What is the sound intensity in decibels of a whisper ?

Normal talking ?

A rock concert ?

How much intense is . Predicting 335911 on the graph , what ( normal talking than a whisper ?

Explain . be If you were exposed to them ?

Sound Level ( decibels ) Whisper Normal Rock Pain Jet Talking Concert Threshold Plane of Sound 618 FIGURE 15 The Ear Sound waves enter the outer ear and make structures in the middle ear vibrate . When the vibrations reach the inner A ewe ear , nerve impulses travel to the cerebrum through the auditory nerve . Predicting What would happen if the bones of the middle ear could not move ?

Ear canal Sump Eardrum Inner Ear a , Mug Vibrations in the Sound waves enter the Vibrations pass from 59 ( em external ear and reach the hammer to the ' the ea , am , and i signals to the brain . The External Ear The three regions of the external ear , middle ear , and inner shown in Figure 15 . Notice that the visible part of the external ear is shaped like a funnel . This shape enables the external ear to collect sound waves , which then travel down the ear canal . The Middle Ear The ear canal directs sound waves to the middle ear , where they strike the eardrum . The eardrum , or tympanic membrane , vibrates when struck by sound waves . Your eardrum vibrates much as a drum does when it is struck . Within the middle ear are three small bones called the hammer ( or malleus ) anvil ( or incus ) and stirrup ( or stapes ) These tiny bones act as a series of levers that transfer vibrations from one place to another . Vibrations pass from the eardrum to the hammer . Then they pass to the anvil , and next to the stirrup . Muscles adjust the tension on the eardrum and the three bones in response to the loudness of the sound . The Inner Ear The stirrup vibrates against a thin membrane that covers the opening of the inner ear , also called the labyrinth . This membrane channels the vibrations into in the cochlea . The ( le uh ) is a tube that is lined with receptor cells that respond to sound . When the in the cochlea vibrates , it stimulates these receptors . Sensory neurons then send nerve impulses to the cerebrum through the auditory nerve . These impulses are interpreted as sounds that you hear . Skills ?

Activity us Making Models Use simple materials to build a model of the ear . Items such as a funnel , clay . pipe cleaners , and a piece of balloon may be used to model different parts of the ear . Make a sketch of your model and label each structure . Then write a brief paragraph that explains how the parts of the ear work together to transmit sound to the brain . Chapter 15 619

The Inner Ear and Balance ' i ' inner ear control your sense of balance . Above the canals cochlea in your inner ear are the semicircular canals . which are the structures in the ear that are responsi ble for your sense of balance . You can see how these structures got their name if you look at Figure 16 . These canals , as well as the two tiny sacs located behind them , are full of . The canals and sacs are also lined with tiny cells that have hairlike extensions . When your head moves , the in the semi circular canals is set in motion . The moving makes the cells hairlike extensions bend . This ing produces nerve impulses in sensory neurons . The impulses travel to the cerebellum . The cerebellum then analyzes the impulses to determine the way your head is moving and the position of your body . If the senses that you are losing your balance , it sends impulses to muscles that help you restore your balance . Have you ever spun around and then stopped FIGURE 16 A suddenly ?

You probably felt dizzy afterward . This tightrope walker is able to keep his ness happens because the in the semicircular balance due the i Of his canals keeps moving for a while after your body stops semicircular canals . Relating Cause and Effect How do the help YOU ' Reading Where in the ear are the semicircular balance ?

canals located ?

moving . A Reading , Writing Vocabulary Skill Use the meaning of the . to explain the meaning of dizziness . Reviewing Key Concepts Sammy hung write a . Listing What are the parts of the eye ?

summary um damp Sequencing Describe the process by which the eye who to your eyes when produces an image . Begin at the point at which light you walk from a dark movie theater is focused by the lens . into moshing , the Predicting If you closed one eye , could you thread a Ideas and important details needle easily ?

Explain your answer . about the structures in the eye Identifying What are the three regions of the ear ?

and how they change . Describing Describe how sound is transmitted from the eardrum to the cochlea . Relating Cause and Effect Why may an infection of the inner ear cause you to lose your balance ?

620 ! Students know organ systems function because of the contributions of individual organs , tissues , and cells . The failure of any part can affect the entire system . How do your senses of smell and taste work together ?

How is your skin related to your sense of touch ?

Key Terms taste bud In Go ( For Links on the senses Visit Web Code Enjoy the ride , and thank your senses ! Smell , Taste , and Touch Standards What in the Bag ?

Your teacher will give you a paper bag that contains several objects . Your challenge is to use only your sense of touch to identify each object . You will not look inside the bag . Put your hand in the bag and carefully touch each object . Observe the shape of each object . Note whether its surface is rough or smooth . Also note other characteristics , such as its size , what it seems to be made of , and whether it can be bent . After you have finished touching each object , write your observations on a sheet of paper . Then , write your inference about what each object is . Think it Over Interpreting Data What did your sense of touch help you learn ?

What could you not determine ?

You grip the steering wheel as the bumper car jerks into motion . The wheel surface feels smooth . Next , you are ping around and bumping into other cars . You feel air rush past your face and the jolt of another car hitting yours . As you zoom to afar corner of the . you smell the aromas of the snack bar . Like your other senses , your senses of smell . taste , and touch get information from your environment . This tion travels by nerve impulses to your brain . Then you can decide how to act on the information . For example , you can choose which way to move the bumper car or when to eat .

Skills Activity Designing Experiments Can people tell one food from another if they can taste the foods but not smell them ?

Design an experiment to find out . Use these foods a peeled pear , a peeled apple , and a peeled raw potato . Be sure to control all variables except the one you are testing . Write your hypothesis and a description of your procedure . Obtain your teacher approval before carrying out your experiment . Smell and Taste You walk into the house and smell the aroma of freshly baked cookies . You bite into one and taste its rich chocolate . When you smelled the cookies , receptors in your nose reacted to chemicals carried by the air from the cookies to your nose . When you took a bite of a cookie , your taste buds were lated . Taste buds are organs on your tongue that respond to chemicals in food . These chemicals were dissolved in saliva , which came in contact with your taste buds . 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 . Nerve impulses then travel to the brain , where they are interpreted as smells or tastes . The nose can distinguish at least 50 basic odors . In , there are only five main taste , sour , salty , bitter , and a taste called umami . When you eat , however , you experience a much wider variety of tastes . The of food is by both smell and taste . When you have a cold , foods may not seem very . That is because a stuffy nose decreases your ability to smell food . What basic tastes can the tongue detect ?

Magnified image of the tongue surface 622 FIGURE 17 Sense of Taste The tongue has numerous visible bumps on its surface . The taste buds are located below the surface of the tongue , on the sides of the bumps . Taste Bud Nerve to brain Chemicals dissolved in saliva trigger taste receptors in the taste buds . The taste receptors send signals to the brain .

Touch Unlike vision , hearing . balance , smell , and taste , the sense of touch is not found in one place . Instead , the sense of touch is found in all areas of your skin . Your skin is your largest sense organ ! Your skin contains different kinds of touch receptors that respond to a number of stimuli . Some of these receptors respond to light touch and others to heavy pressure . Still other receptors pick up sensations of pain and temperature change . The receptors that respond to a light touch are close to the surface of your skin . They tell you when something brushes against your skin . These receptors also let you feel the textures of objects . such as smooth glass and rough sandpaper . Receptors deeper in the skin pick up the feeling 13 of pressure . Press down hard on the top of your desk , for Reading by Touch example , and you will feel pressure in your . 59 ' 59 . of touch to read . To do this , they run The skin also contains receptors that respond to their written in and pain . Pain is unpleasant , but it can be one of , mine use , dot , to the body most important feelings because it alerts the body represent letters and numbers . Here , to possible danger . Have you ever stepped into a bathtub of blind Child very hot water and then immediately pulled your foot out ?

read Bram If so , you can appreciate how pain can trigger an important response in your body . Assessment Target Reading Skill identify Main Ideas Drawing Conclusions The brain itself has Reread the text following the heading Touch . no pain receptors . What can you conclude Which sentence states the main idea ?

about the brain from this information ?

Reviewing Key Concepts is . Reviewing What two senses work together to the of food ?

Comparing and Contrasting How are the senses of taste and smell similar ?

How are Ai ' Activity they different ?

Light Touch Ask family members to keep ( sequencing the Process by which their while you help them touch you are able to taste food . Begin at the point when you Put Piece offood into your mouth Choose different items , such as a metal Identify each of the key involved . fE fab ' Identifying What kinds of touch receptors , apple ' fa ly are found in the skin ?

that they can feel the differences in texture . Relating Cause and Effect What happens ' a ' the , of in the Skin when you much a the different receptors present in skin . hot stove ?

Chapter 15 623 Section Integrating Health and Other Drugs Focus Students know organ What IS Al ( fed ?

systems function because of the Look at the to he contributions of individual organs , It ' es the me tissues , and cells . The failure of any re pe part can affect the entire system . changes in reaction time . Which body system is immediately me ' the me endangered by drug abuse ?

takes someone to respond in What are some commonly abused ' drugs and how does each affect . HOW does the percent of the body ?

alcohol in the blood change How does alcohol abuse harm Om ' in the the body ?

graph ?

Blood Alcohol Concentration ( 96 ) Describe how reaction time Key Terms changes as the alcohol level in the blood changes . What is the drug difference between the least and greatest change in reaction drug abuse time ?

tolerance Think over addiction . I Inferring How might alcohol affect a person ability to drive re ' safely ?

Explain your answer . stimulant alcoholism Drugs ! You probably hear and see that word in a lot of places . Drugstores sell drugs to relieve headaches , soothe upset ( and stop coughs . Radio and television programs and ma azine articles lore dru . Your school probably has a program to educate students about drugs . When eo le talk about dru , what do the mean ?

To a , a drug is any chemical taken into the body that causes changes in a persons body or behavior . Many drugs affect the . functioning of the central nervous system . Drug Abuse The deliberate misuse of drugs for purposes other than cal ones is called drug abuse . Even medicines can be abused drugs if they are used in a way for which they were not intended . Many abused drugs , however , such as cocaine and heroin , are illegal under any circumstances . The use of these drugs is against the law because their effects on the body are almost always dangerous . 624 .

ed Drugs abused drugs . such as marijuana , alcohol , and cocaine , are especially dangerous because of their immediate effects on the brain and other parts of the nervous system . In addition , drug abuse can lead to addiction and other health and social problems . drugs have different effects . Some drugs cause nausea and a fast , irregular heartbeat . Others can cause sleepiness . Drug abusers may also experience headaches , dizziness , and trembling . Alcohol can cause confusion , poor muscle coordination , and blurred vision . These effects are especially dangerous in tions in which an alert mind is essential , such as driving a car . Most abused drugs can alter , or change , a persons mood and feelings . For example , alcohol can sometimes make a son angry and even violent . drugs also affect of thinking and interpretation information from the senses . Tolerance and Addiction If a person takes a drug regularly , the body may develop a tolerance to the drug . Tolerance is a state in which a drug user needs larger and larger amounts of the drug to produce the same effect on the body . Tolerance can cause people to take too much , or an overdose , of a drug . People who take an overdose may become unconscious or even die . Repeated use of some abused drugs can lead to addiction . a condition in which the body becomes physically dependent on a drug . If a person stops using a drug suddenly , headaches , dizziness , fever , vomiting , and muscle cramps may result . These symptoms are signs of withdrawal , a period of ment that occurs when a person stops taking a drug on which the body is dependent . Some drugs may also cause a person to become emotionally dependent on them . What is addiction ?

Ni Communicating Plan a television commercial aimed at teenagers to help them avoid the pressure to try drugs . Your commercial should reveal some harmful effects of drugs and give strategies for avoiding drugs . Create several storyboards to show what the commercial will look like . Then , write a script for your commercial . FIGURE 19 Drug Abuse Drug abuse can have serious consequences . However , if someone is abusing drugs , there are ways to help that person . Interpreting Diagrams What are two ways you can help if someone you know is abusing drugs ?

( Go ' CED For Links on drug addiction Visit Web Code FIGURE 20 Making a Statement About Abuse Many teens are becoming active in antidrug campaigns . Kinds of Abused Drugs There are many kinds of drugs , with a wide range of effects on the body . Some are legitimate medicines that a doctor prescribes to help the body disease and injury . However , many kinds of drugs are frequently abused . Commonly abused drugs include depressants , stimulants , hallucinogens , anabolic steroids , and alcohol . Many drugs affect the central nervous system , while others affect the overall chemical balance in the body . Figure 21 lists and describes characteristics of some commonly abused drugs . Depressants Notice in Figure 21 that some drugs are as depressants . Depressants are drugs that slow down the activity of the central nervous system . When people take depressants , their muscles relax and they may become sleepy . They may fail to respond to stimuli in a normal amount of time . For example , depressants may prevent people from reacting quickly to the danger of a car rushing toward them . Alcohol and narcotics , such as heroin , are depressants . Stimulants In contrast to depressants , stimulants speed up body processes . They make the heart beat faster and make the breathing rate increase . Cocaine and nicotine are stimulants , as are amphetamines ( am ET uh ) Amphetamines are prescription drugs that are sometimes sold illegally . and Some substances , called , produce effects when they are inhaled , or breathed in . include paint thinner , nail polish remover , and some kinds of cleaning . gens , such as and mescaline , can make people see or hear things that do not really exist . Steroids Some athletes try to improve their performance by taking drugs known as steroids . Anabolic steroids ( an uh BAH lik STEER ) are synthetic chemicals that are similar to hormones produced in the body . Anabolic steroids may increase muscle size and strength . However , steroids can cause mood changes that lead to . In addition , steroid abuse can cause serious health problems , such as heart damage , liver damage , and increased blood pressure . Steroid use is especially dangerous for teenagers , whose growing bodies can be permanently damaged . winch , What kinds of drugs are classified as stimulants ?

Ficus 21 Abused drugs can have many serious effects on the body . Most of the drugs listed below cause addiction and emotional dependence . Interpreting Tables What are the effects of using Some Effects of Commonly Abused Drugs a Marijuana Unclear thinking , loss of ( including hashish ) coordination , increased heart rate I I Difficulty with concentration and memory respiratory disease and lung cancer Stimulant nausea . loss of appetite , headache From tobacco smoke heart and lung disease , difficulty breathing , heavy coughing Depressant decreased alertness , poor reflexes , nausea , emotional depression ( glue . Sleepiness . nausea , headaches . Damage to , kidneys , and brain household cleaners ) loss of , death loss of bladder control Liver and brain damage , heart disease , digestive problems , inadequate nutrition Mental illness , damage to lining of nose , irregular heartbeat , heart or breathing failure , liver damage Restlessness . irritability , Irregular heartbeat , liver damage Cocaine Stimulant nervousness . including crack ) disturbed sleep , loss of appetite ?

Psychotic behavior , memory loss , aggression , damage to brain and heart , severe tooth and gum disease , stroke Methamphetamine Increased respiration , elevated ( crystal meth ) body temperature , stroke , anxiety , panic ( thoughts and actions not ) connected to reality Mental fearfulness behavioral changes , including violence Barbiturates Depressant decreased alertness . Phenobarbital , slowed thought processes , Seconal ) poor muscle coordination , irritability , confusion Depressant blurred vision . sleepiness . unclear speech , headache . skin rash Blood and liver disease opiates ( Depressant sleepiness nausea ' reduced respiration I I heroin ) Heart , liver , and kidney damage hypertension overgrowth of skull and facial bones aggression Constipation , convulsion , coma , death Anabolic steroids Chapter 15 627

FIGURE 22 Effects Alcohol affects every system of the body . It also impacts a thought processes , judgment . and reaction time . In the bottom photo , a police officer tests the blood alcohol concentration of a driver suspected of drinking . 628 Alcohol Alcohol is a drug found in many beverages , including beer , wine , cocktails , and hard liquor . Alcohol is a powerful sant . all states , it is illegal for people under the age of 21 to buy or possess alcohol . in spite of this fact , alcohol is the most commonly abused legal drug in people aged 12 to 17 . How Alcohol Affects the Body Alcohol is absorbed by the digestive system quickly . If a person drinks alcohol on an empty stomach . the alcohol enters the blood and gets to the brain and other organs almost immediately . If alcohol is drunk with a meal , it takes longer to get into the blood . The chart in Figure 22 describes what alcohol does to the body . The more alcohol in the blood , the more serious the effects . The amount of alcohol in the blood is usually expressed as blood alcohol concentration , or BAC . A BAC value of percent means that one tenth of one percent of the in the blood is alcohol . in some states , if car drivers have a BAC percent or more . they are legally drunk . In other states , drivers with a BAC of are considered legally drunk . Alcohol produces serious negative effects , including loss of normal judgment , at a BAC of less than percent . This loss of judgment can have serious consequences . People who have been drinking may not realize that they can not drive a car safely . About every two minutes , a person in the United States is injured in a car crash related to alcohol . Effects of Alcohol Effect Cardiovascular First , heartbeat rate and blood pressure increase . Later , they may decrease . Alcohol is absorbed directly from the stomach and small intestine , which allows it to enter the bloodstream quickly . The kidneys produce more urine , causing the drinker to excrete more water than usual . Digestive system Excretory system Vision blurs . Speech becomes unclear . Control of behavior is reduced . Judgment becomes poor . Nervous system skin Blood flow to the skin increases , causing rapid loss of body heat .

Alcohol Abuse Many adults drink Hum , um ally and in moderation , without serious safety or health . However , heavy drinking , especially over a long period , can result in health problems . Alcohol abuse can cause the destruction of cells in the brain and liver , and can lead to addiction and emotional dependence . Damage to the brain can cause mental disturbances , such as tions and loss of consciousness . The liver , which breaks down alcohol for elimination from the body , can become so scarred that it fails to function properly . Liver failure affects body and processes . For example , without certain chemicals produced by the liver , blood may not clot properly . In tion to liver and brain damage , alcohol abuse can increase the risk of getting certain kinds of cancer . Abuse of alcohol can result in alcoholism . a disease in which a person is both physically addicted to and emotionally dependent on alcohol . To give up alcohol , as with any tive drug , alcoholics must go through withdrawal . To give up FIGURE 23 drinking , alcoholics need both medical and emotional help . alcohol abuse can cause Medical professionals , psychologists , and organizations such damage to the as Alcoholics Anonymous can help a person stop drinking . naming cause and , other effects can alcohol abuse ci Li . What organs are affected by alcohol abuse ?

have on the body ?

Assessment ix Vocabulary One meaning the Inferring Why might a persons risk of a heart verb depress is to decrease the force or activity attack increase with the use of stimulants ?

If you add the suffix to the verb depress , what a . Reviewing What type of drug is alcohol ?

Key Term do you get ?

What is the meaning of this . Explaining What immediate effects does Key Term ?

alcohol have on the body ?

Relating Cause and Effect Based on alcohol effect on the nervous system . explain why drinking and driving is extremely dangerous . Reviewing Key Concepts Identifying Which major organ of the body is quickly affected by commonly abused drugs ?

Applying Concepts What reasons would you give to discourage someone from abusing drugs ?

a . Listing Name two commonly abused depressants and two commonly abused stimulants . Comparing and Contrasting Contrast the effects that depressants and stimulants have on the body . i Activity Medicine Labels With a family member , collect several medicine bottles found in your home . Read the warning labels and then discuss them with your family . Identify which body systems could be placed at risk by use of these medicines . Why do you think medicines provide warnings ?

Chapter 15 629 Chapter 15 Study Guide . that enable the nervous system to function include the BIG How the Nervous System Works ( Key Concepts The nervous system directs how your body responds to information about what is happening inside and outside your body . Your nervous system also helps maintain homeostasis . The three kinds of neurons found in the body are sensory neurons . and motor neurons . For a nerve impulse to be carried along at a synapse , it must cross the gap between an axon and the next structure . Key Terms stimulus response neuron nerve impulse dendrite axon nerve sensory neuron motor neuron synapse Divisions of the Nervous System Key Concepts The central nervous system is the control center of the body . It includes the brain and spinal cord . The three main regions of the brain are the cerebrum , cerebellum , and brain stem . 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 . A reflex is an automatic response that occurs very rapidly and without conscious control . and spinal cord injuries are two ways the central nervous system can be damaged . Key Terms central nervous system peripheral nervous system brain spinal cord cerebrum cerebellum brain stem somatic nervous system autonomic nervous system concussion 630 brain , spinal cord . neurons , and sense organs , such as the eye and ear . Sight and Hearing Key Concepts , The eyes convert light into nerve impulses that your brain interprets , enabling you to see . The ears convert sound into nerve impulses that your brain interprets . enabling you to hear . Structures in your inner ear control your sense of balance . Key Terms cornea pupil iris lens retina rods cones optic nerve eardrum hammer anvil stirrup cochlea semicircular canal Smell . Taste , and Touch Key Concepts ! The senses of smell and taste work together when chemicals in food or in the air trigger receptors in the nose and mouth . The skin contains touch receptors that respond to a number of stimuli . Key Terms taste bud Alcohol and Other Drugs ( Key Concepts Most abused drugs are dangerous because of their immediate effects on the nervous system . Commonly abused drugs include depressants . Stimulants . steroids , and alcohol . Alcohol use can destroy cells in the brain and liver , and lead to addiction . Key Terms drug drug abuse tolerance addiction withdrawal depressant stimulant alcoholism

For I Visit Web Code . Target Reading Skill Identifying Main Ideas Review the two paragraphs following the heading Concussions on page 613 . Use a graphic organizer like the one to the right to identify the main idea I ! and three details . a Reviewing Key Terms Choose the letter of the best answer . Complete the following sentences so that . The structures that carry messages toward a ' a ' haw Phi the ' 31 ?

Answering the door when the bell rings is an example of a response , which is . dendrites . Your understanding of the words on this page ' occurs in your cerebrum , which is . Which structure links the brain to most of the I . nervous system ?

i the . Sound waves strike the eardrum , which then the cochlea ' the spinal cord 10 . Alcohol is as a depressant because . Which structure focuses light as it passes through the eye ?

the pupil the retina the , Writing in Science ' contain sensory receptors that om . diagram of the human eye . and label the pans . Than , write a paragraph describes how each part helps a poison see an Image . heat . Physical dependence on a drug is called withdrawal . response . addiction . tolerance . Chapter 15 631

Review and Assessment Checking Concepts Applying Skills 11 . Compare the functions of axons and dendrites . use the graph to answer Questions . How do the and cerebellum work A person with normal vision stood at together when you ride a bicycle ?

distances from an eye chart and tried to the . I . is me function of the autonomic letters on the chart The line graph gives the nervous system ?

Eye Chart Results 14 . What is the result if the spinal cord is cut ?

15 . What enables a person to see depth ?

100 16 . What type of stimuli trigger receptors that enable you to taste food ?

17 . How do anabolic steroids affect the body ?

Thinking Critically 18 . Interpreting Diagrams The diagram below shows a synapse . Explain how a nerve impulse crosses the gap . Distance ( 22 . Reading Graphs What variable is plotted on the ?

On the ?

23 . Interpreting Data As the distance from the eye chart increases , what happens to the percentage of letters correctly ?

24 . Controlling Variables What was the manipulated variable in this experiment ?

What was the responding variable ?

19 . Relating Cause and Effect When a person has a stroke , blood to part of the brain is 25 . Predicting Based on the graph , what would reduced , and some brain gens dig suppose that you expect the percent of correctly suck , a woman is unable to move her letters to be when the distance is 12 meters ?

right arm and right leg . In which side of her brain did the stroke occur ?

Explain . St I ti 20 . Applying Concepts As a man walks barefoot along a beach , he steps on a sharp shell . His foot automatically jerks upward , even before he feels pain . What process is this an example of ?

How does it help protect the man ?

Performance Assessment Explain to your classmates how you set up your experiment , I which illusions you used , which senses were 31 ' Suppose a person has an injury that involved in the illusions . and the illusions results in a torn eardrum . Explain how you worked . lnclude information on how the nervous think the person hearing would be affected . system was involved in your illusions . 6320 ,

Standards Practice Choose the letter of the best answer . A scientist studying the brain is studying part of the A peripheral nervous system . somatic nervous system . autonomic nervous system . central nervous system . Suppose you step on a tack . Which of the following choices represents the order of response of your nervous system ?

A Sensory neuron stimulated impulse to spinal cord impulse to brain impulse to motor neuron foot moves Sensory neuron stimulated impulse to spinal cord impulse to motor neuron foot moves message to brain Impulse to motor neuron foot moves impulse to sensory neuron impulse to spinal cord impulse to brain Foot moves sensory neuron stimulated impulse to brain impulse to motor neuron . What is the function of the part labeled A on the neuron shown below ?

A It carries the nerve impulse toward the cell body . It protects the neuron from damage . It carries the nerve impulse away from the cell body . It picks up stimuli from the environment . Success , It Use the diagram below and your knowledge of science to answer Question . Light Rays . The person with this eye probably has trouble seeing because the light rays focus A behind the retina . on the cornea . on the eyes lens . on the iris . A disease damages a person semicircular canals . That person will most likely have difficulty A seeing . hearing . maintaining balance . tasting food . Which of the following structures in the ear changes sound waves into nerve impulses that go to the brain ?

A hammer cochlea eardrum anvil . You can infer that a person who has lost his or her sense of smell is also likely to have a poor A sense of balance . sense of touch . sense of taste . sense of hearing . Identify the structures of the eye and other parts of the nervous system that allow you to read and understand this sentence . Explain the order in which the structures are involved and how each one functions . Chapter 15 633