Section

1

How theNervous System Works

Objectives

After this lesson, students will be able to

D.6.1.1

Identify the functions of the nervous system.

D.6.1.2

Describe the structure of a neuron and the kinds of neurons found in the body.

D.6.1.3

Explain how nerve impulses travel from one neuron to another.

Target Reading Skill

Previewing Visuals

Explain that looking at the visuals before they read helps students activate prior knowledge and predict what they are about to read.

Answers

Sample questions and answers:

What is a sensory neuron?

(A neuron that picks up stimuli from the internal or external environment and converts each stimulus into a nerve impulse)

What does an interneuron do?

(It carries nerve impulses from one neuron to another.)

Teaching Resources

•

Transparency D48

Preteach

Build Background Knowledge

Reactions to the Environment

Ask:

What does it mean when someone says that something makes them nervous?

(Students may say it means that a person is anxious or worried about something.)

Explain that anxiety and worry are different ways in which people react to their environment. Point out that the nervous system allows people to react to their environment in various ways.

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Skills Focus

Inferring

Materials

paper, pencil, penny

Time

15 minutes

Tips

Remind students to follow directions carefully as they complete the activity.

Think It Over

Sample answer: Sense organs used include eyes and skin. Muscle movements include the muscles of the

arms and hands holding the penny down, moving the penny from place to place, picking up the pencil, and tracing the circle. Thought processes involved include reading and understanding the instructions, choosing where to place the penny, and following the sequence of numbers. The nervous system coordinated all these processes.

1 How the Nervous System Works

The ball whizzes toward the soccer goalie. She lunges for theball, and in one swift movement blocks it from entering thenet. To tend goal, soccer players need excellent coordinationand keen vision. In addition, they must remember what theyhave learned from years of practice.

Whether or not you play soccer, you too need coordination,memory, and the ability to learn. Your nervous system carriesout all these functions. The nervous system includes the brain,spinal cord, and nerves that run throughout the body. It alsoincludes sense organs, such as the eyes and ears.

Functions of the Nervous SystemThe Internet lets people gather information from anywhere inthe world with the click of a button. Like the Internet, yournervous system is a communications network. But it is muchmore efficient than the Internet.

The nervous system receives information about what ishappening both inside and outside your body. It also directsthe way in which your body responds to this information. Inaddition, your nervous system helps maintain homeostasis.Without your nervous system, you could not move, think, feelpain, or taste a spicy taco.

The Path of a Nerve Impulse

A.

Q.

Q.

What is a sensory neuron?

How Simple Is a Simple Task?1. Trace the outline of a penny in twelve different places on a

piece of paper.2. Number the circles 1 through 12. Write the numbers

randomly, in no particular order.3. Now, pick up the penny again. Put it in each circle, one after

another, in numerical order, beginning with 1 and ending with 12.

Think It OverInferring Make a list of all the sense organs, muscle movements, and thought processes used in this activity. Compare your list with your classmates’ lists. What organ system coordinated all the different processes involved in this task?

Reading PreviewKey Concepts• 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?

Key Terms• stimulus • response• neuron • nerve impulse • dendrite • axon • nerve• sensory neuron • interneuron • motor neuron • synapse

Target Reading SkillPreviewing Visuals Before you read, preview Figure 3. Then, write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions.

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Differentiated Instruction

Instruct

Functions of the Nervous System

Teach Key Concepts

Receiving and Responding to Information

Focus

Ask:

Why do you need to communicate when you play team sports?

(Sample answers: The coach needs to call plays. Players need to signal to one another.)

Teach

Explain that your body needs a communication system, too. The nervous system receives messages and responds to them. Ask:

If you touched a hot object, what would be the stimulus?

(Heat from the object)

The response?

(Jerking away from the object)

Remind students that homeostasis is the process of maintaining stable internal conditions. Ask:

When you run, how does your breathing change?

(You breathe faster and deeper.)

Explain that your nervous system causes this change because the muscles are using more oxygen.

Apply

Have students identify the stimulus and response in the following situations:

tasting a lemon wedge

(Sour taste; mouth fills with saliva);

smelling vinegar

(Sour smell; nose wrinkles);

someone throwing a ball toward you

(Speed and direction of ball; you catch the ball).

learning modality: logical/mathematical

Independent PracticeTeaching Resources

•

Guided Reading and Study Worksheet:

How the Nervous System Works

Student Edition on Audio CD

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Less Proficient Readers

Reviewing the Section

Before students read the section, have them jot down the headings and subheadings. As they read, have them list one or two details under each heading.

learning modality: verbal

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Special Needs Interpreting Diagrams

The figures in this lesson are important in helping to clarify information. Pair visually impaired students with sighted students as they read this lesson. Sighted students can explain what is happening in each of the figures.

learning modality: verbal

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Oral Presentation

Call on students to name the three functions of the nervous system and give examples of each.

Answers

Figure 1

It directs her body to respond appropriately to the information it receives.

A change or signal in the environment that can make

an organism react

Maintaining HomeostasisThe goalie’s nervous system adjusts her breathing and heart rate to meet her energy needs throughout the game.

Responding to InformationThe nervous system causes a response, and the goalie reaches out to block the shot.

Receiving InformationThe goalie’s eyes receive information that a soccer ball is zooming toward her.

Receiving Information Because of your nervous system,you are aware of what is happening in the environment aroundyou. For example, you know that a fly is buzzing around yourhead, that the wind is blowing, or that a friend is telling afunny joke. Your nervous system also checks conditions insideyour body, such as the level of glucose in your blood.

Responding to Information Any change or signal in theenvironment that can make an organism react is called astimulus (STIM yoo lus) (plural: stimuli). A buzzing fly is astimulus. After your nervous system analyzes the stimulus, itcauses a response. A response is what your body does in reac-tion to a stimulus—you swat at the fly.

Some nervous system responses, such as swatting a fly, arevoluntary, or under your control. However, many processesnecessary for life, such as heart rate, are controlled by involun-tary actions of the nervous system.

Maintaining Homeostasis The nervous system helpsmaintain homeostasis by directing the body to respond appro-priately to the information it receives. For example, when youare hungry, your nervous system prompts you to eat. Thisaction maintains homeostasis by supplying your body with thenutrients and energy it needs.

What is a stimulus?

FIGURE 1The 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’s nervous system help her body maintain homeostasis?

The Neuron

Teach Key Concepts

Types of Neurons

Focus

Remind students that the nervous system receives and transmits messages all through the body.

Teach

Ask:

What are the parts of a neuron?

(Nucleus, axon, dendrite)

What do axons and dendrites do?

(Axons carry impulses away from the cell body. Dendrites carry impulses toward to the cell body.)

Where does the message from a sensory neuron end up?

(In the brain or spinal cord)

Where does a motor neuron send an impulse?

(A muscle or gland)

Apply

Have students identify which type of neuron, sensory or motor, would conduct the message in the following situations:

Seeing a picture

(sensory);

feeling pain from skinning your knee

(sensory);

moving your arm to catch a ball

(motor).

learning modality: logical/mathematical

Teaching Resources

•

Transparency D49

Classifying Neuron Types

Materials

notecards, markers

Time

10 minutes

Focus

Review the three types of neurons.

Teach

Divide the class into three groups, and assign each group to portray a type of neuron. Challenge students to model how nerve impulses are sent through the body. Explain that students in the sensory neuron group will write descriptions of stimuli and then pass their notes to students representing interneurons. The interneuron group will then pass the notes to students playing motor neurons, who write notes describing responses. (Example: Sensory group writes “You feel a hot stove”; interneuron group passes the note to motor group, who writes “Remove hand from stove.”)

Apply

After groups have modeled several actions, have a member of each group draw on the board the sequence of one of the actions. Ask the student to include how the message traveled along axons and dendrites.

learning modality: kinesthetic

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The NeuronYour nervous system includes various organs, tissues, and cells. Forexample, your brain is an organ, and the nerves running through-out your body are tissues. The cells that carry information throughyour nervous system are called neurons(NOO rahnz), or nervecells. The message that a neuron carries is called a nerve impulse.

The Structure of a Neuron The structure of a neuron en-ables it to carry nerve impulses. A neuron has a large cell bodythat contains the nucleus, threadlike extensions calleddendrites, and an axon. The dendrites carry impulses toward theneuron’s cell body. The axon carries impulses away from the cellbody. Nerve impulses begin in a dendrite, move toward the cellbody, and then move down the axon. A neuron can have manydendrites, but it has only one axon. An axon, however, can havemore than one tip, so the impulse can go to more than oneother cell.

Axons and dendrites are sometimes called nerve fibers. Nervefibers are often arranged in parallel bundles covered with connec-tive tissue, something like a package of uncooked spaghettiwrapped in cellophane. A bundle of nerve fibers is called a nerve.

Kinds of Neurons Three kinds of neurons are found in thebody—sensory neurons, interneurons, and motor neurons.Figure 3 shows how these three kinds of neurons work together.

A sensory neuron picks up stimuli from the internal or exter-nal environment and converts each stimulus into a nerve impulse.The impulse travels along the sensory neuron until it reaches aninterneuron, usually in the brain or spinal cord. An interneuronis a neuron that carries nerve impulses from one neuron toanother. Some interneurons pass impulses from sensory neu-rons to motor neurons. A motor neuron sends an impulse to amuscle or gland, and the muscle or gland reacts in response.

What is the function of an axon?

How a Nerve Impulse TravelsEvery day of your life, billions of nerve impulses travel throughyour nervous system. Each of those nerve impulses begins inthe dendrites of a neuron. The impulse moves rapidly towardthe neuron’s cell body and then down the axon until it reachesthe axon tip. A nerve impulse travels along the neuron in theform of electrical and chemical signals. Nerve impulses cantravel as fast as 120 meters per second!

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Cell body

Dendrites

Nucleus

Axon

Axon tips

For: More on nerve impulsesVisit: PHSchool.comWeb Code: ced-4061

PHSchool.com

FIGURE 2Structure of a Neuron A neuron has one axon and many dendrites that extend from the cell body.

Differentiated Instruction

PHSchool.com

How a Nerve Impulse Travels

Teach Key Concepts

Transmission Across Synapses

Focus

Review the sequence of an impulse within a nerve cell (dendrite to cell body to axon).

Teach

Ask:

What carries an impulse across

the synapses?

(Chemicals released from the axons)

What would happen if the chemical were not available?

(The nerve impulse would stop.)

Where can impulses be received?

(Other dendrites, muscles, or cells in another organ)

Apply

Ask:

Why is pain not experienced in an area after an injection to numb the area is given by a doctor?

(The chemicals in the injection may affect neurotransmitters, thereby causing the sensory neurons in the area not to

sense pain.)

learning modality: verbal

Use Visuals: Figure 3

Tracing the Path of Nerve Impulses

Focus

Refer students to Figure 3.

Teach

Have students trace the path of the nerve impulse. Ask:

What is the stimulus to which each kind of neuron responds?

(Sensory neurons respond to the ringing sound of the phone. Interneurons respond to the impulses from the sensory neurons. Motor neurons respond to impulses from interneurons.)

Apply Have students measure on their bodies the distance the nerve impulse travels from the ear to the brain, and to the hand. learning modality: visual

Teaching Resources

• Transparency D50

For: More on nerve impulsesVisit: PHSchool.comWeb Code: ced-4061

Students can review nerve impulses in an online interactivity.

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English Learners/BeginningComprehension: Key Concepts Emphasize that a nerve cell is the same as a neuron, but not the same as a nerve or a nerve fiber. Show students a piece of cable with the insulation removed as you explain the differences between these structures. learning modality: visual

L1 English Learners/IntermediateVocabulary: Science Glossary Encourage students to compile a section glossary that includes all the Key Terms, then write definitions for each term in English and in their native language. learning modality: verbal

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AnswersFigure 3 To the interneurons

An axon carries a nerve impulse away from the cell body.

Receptors in ear

3 Motor neuronImpulses 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.

1 Sensory NeuronNerve 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.

2 InterneuronFrom the sensory neurons, the nerve impulse passes to interneurons in the brain. Your brain interprets the impulses from many interneurons and makes you realize that the phone is ringing. Your brain also decides that you should answer the phone.

1

2

3

Muscle in hand

FIGURE 3

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

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Assess

Reviewing Key Concepts1. a. Receive information about internal and external events, respond to this information, and maintain homeostasis b. Sample answer: The stimulus is seeing a ball being thrown toward you. The nervous system sends messages, and the brain analyzes the stimulus. The body responds by making your arm move to catch the ball. c. You would have to think all the time about keeping your heart beating and adjusting its rate in response to changing events.2. a. Sensory neurons, interneurons, and motor neurons b. A sensory neuron detects a stimulus and sends an impulse that travels to interneurons and then to motor neurons, which send the nerve impulse to a muscle or gland. c. A sensory neuron picks up a stimulus from the internal or external environment, converts it into an impulse, and sends the impulse to the nervous system. A motor neuron sends an impulse to muscles or glands.3. a. The junction where one neuron can transfer an impulse to another neuron.b. (1) A nerve impulse reaches the tip of an axon. (2) Chemicals are released into the gap at the synapse. (3) The chemicals carry the nerve impulse across the gap to the next structure.

ReteachHave students find facts from the section to support the following statement: The neurons that make up the nervous system act as a transportation system.

Performance AssessmentOral Presentation Ask pairs of students to choose an everyday action, create posters that illustrate the path of the nerve impulses that action involves, and then present the posters to the class.

Teaching Resources

• Section Summary: How the Nervous System Works

• Review and Reinforce: How the Nervous System Works

• Enrich: How the Nervous System Works

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Pass the Salt, Please Make sure students define stimulus and response for their families. Students may realize that if they say “Thank you” when the salt and pepper are passed, the passing is a stimulus and the thanks is a response.

Section 1 Assessment

Target Reading Skill Previewing Visuals Refer to your questions and answers about Figure 3 to help you answer Question 2 below.

Reviewing Key Concepts1. a. Listing What are three functions of the

nervous system?b. Describing Give an example of a stimulus

and describe how the nervous system produces a response.

c. 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?

2. a. Identifying Identify the three kinds of neurons that are found in the nervous system.

b. Explaining How do the three kinds of neurons interact to carry nerve impulses?

c. Comparing and Contrasting How do sensory neurons and motor neurons differ?

3. a. Reviewing What is a synapse?b. Sequencing Outline the steps by which a

nerve impulse reaches and then crosses the gap at a synapse.

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Pass the Salt, Please During dinner, ask a family member to pass the salt and pepper to you. Observe what your family member then does. Explain that the words you spoke were a stimulus and that the family member’s reaction was a response. Discuss other examples of stimuli and responses with your family.

Dendrite

Synapse

Dendrite

Chemical carrying impulse

Axon tip

Axon tip

FIGURE 4The 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 impulsereaches the axon tip at the end of a neuron? At thatpoint, the impulse can pass to the next structure.Sometimes the structure is the dendrite of anotherneuron. Other times, the structure is a muscle or a cellin another organ, such as a sweat gland. The junctionwhere one neuron can transfer an impulse to anotherstructure is called a synapse (SIN aps).

How an Impulse is Transferred Figure 4 shows asynapse between the axon tip of one neuron and thedendrite of another neuron. Notice that a small gap sep-arates these two structures. For a nerve impulse to becarried along at a synapse, it must cross the gapbetween the axon and the next structure. The axontips release chemicals that carry the impulse acrossthe gap.

You can think of the gap at a synapse as a river, andan axon as a road that leads up to the riverbank. Thenerve impulse is like a car traveling on the road. To getto the other side, the car has to cross the river. The cargets on a ferry boat, which carries it across the river. Thechemicals that the axon tips release are like the ferry,carrying the nerve impulse across the gap.

Ready or Not!

Prepare for InquiryKey ConceptAn individual’s behaviors can be affected by various factors such as time of day.

Skills ObjectivesStudents will be able to• develop hypotheses about the effect of time

of day on reaction times, and control variables as they test those hypotheses

• draw conclusions about the effect of time of day on response time

Prep Time none

Class Time 50 minutes

SafetyRemind students to take care whiledropping or catching the meter stick.

Review the safety guidelines in Appendix A.

Teaching Resources

• Lab Worksheet: Ready or Not!

Guide InquiryInvitationAsk: What are some situations when a quick reaction time would be advantageous? (Sample answers: Applying the brakes to a car to avoid an accident; catching a falling object)

Introduce the ProcedureTell students that in Part 1 they should test each person at least five times, and then take the average of all trials.

Troubleshooting the ExperimentAdvise students to hold the stick in the same position for every trial.

Extend the InquiryMore to Explore Advise students to use simple arithmetic calculations because they give more consistent results than more complex calculations. Also, discuss why students cannot use the same calculations more than once with each person tested.

Analyze and Conclude1. Stimulus—sight of the dropping stick; response—grabbing the stick. The response is voluntary. The person consciously chooses to do it.

2. Some students may hypothesize that time of day has no effect on reaction times. Others may hypothesize that reaction times are fastest at a particular time of day.

3. All variables need to be controlled except the time of day so that any differences in

reaction time can be directly attributed to the time of day.

4. Sample answer: Yes, reaction times vary. Research indicates that the reaction times of an individual do vary during the day.5. Sample answer: If people’s thumbs and forefingers are at zero at the time of the drop, the number of centimeters the stick drops will be directly proportional to the reaction time because the stick always falls at the same rate.

Ready or Not!

ProblemDo people’s reaction times vary at different times of the day?

Skills Focusdeveloping hypotheses, controlling variables, drawing conclusions

Material• meter stick

Procedure PART 1 Observing a Response to a

Stimulus

1. Have your partner hold a meter stick with the zero end about 50 cm above a table.

2. Get ready to catch the meter stick by posi-tioning the top of your thumb and forefin-ger just at the zero position, as shown in the photograph.

3. 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.

PART 2 Designing Your Experiment

4. With your partner, discuss how you can use the activity from Part 1 to find out whether people’s reaction times vary at different times of day. Consider the questions below. Then, write up your experimental plan.• What 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?

5. Submit your plan for your teacher’s review. Make any changes your teacher recom-mends. Create a data table to record your results. Then, perform your experiment.

Analyze and Conclude1. Inferring In this lab, what is the stimulus?

What is the response? Is the response volun-tary or involuntary? Explain.

2. Developing Hypotheses What hypothesis did you test in Part 2?

3. Controlling Variables In Part 2, why was it important to control all variables except the time of day?

4. Drawing Conclusions Based on your results in Part 2, do people’s reaction times vary at different times of the day? Explain.

5. Communicating Write a paragraph to explain why you can use the distance on the meter stick as a measure of reaction time.

More to ExploreDo 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 teacher’s permission before carrying out your investigation.

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