domain 2: biopsychology

57a

Background/Significance

Many psychologists believe that to truly understand human behavior, one must have an understanding of the biological processes that underlie our actions. While this viewpoint has increasingly dominated the psychological field, students sometimes neglect this important connection. They seem to separate the psychological from the biological.

The National Standards for High School Psychology Curricula, developed by the American Psychological Association, emphasize the importance of helping students understand the underlying biological processes that shape behavior. When choosing modules to teach from this domain, it is suggested that teachers place emphasis on those devoted to these processes, such as Modules 4 and 5. These units reveal the internal workings of the brain and how our bodies adapt to external conditions. Focusing on these units early in the course allows instruc-tors to refer to biological processes when teaching later units, such as development or abnor-mal behavior.

If time allows, it is also suggested that teachers include additional units that will further highlight the important connection between physiological processes and behavior. Thus, teachers may wish to include Modules 6 and 7. These modules focus on how our brains inter-pret environmental sensations.

Modules 8, 9, and 10 may seem like they do not belong in the Biopsychology Domain, but recent research into the underlying mechanisms of consciousness shows just how intercon-nected biological and cognitive processes are. Much of the current research into consciousness examines the ways in which our brains process stimuli in conscious and nonconscious ways. Students need to learn how sleep, body rhythms, psychoactive drugs, and other states of con-sciousness can affect their normal, waking life.

Emphasizing modules that illustrate these issues will help students understand the critical connection between the many biological and psychological forces that affect their everyday behavior.

DOMAIN 2: Biopsychology

B2E3e_book_ATE.indb 2 3/19/12 11:25 AM

DOMAIN 2

57b

Teaching WiTh The STandardS

Biological Bases of Behavior

Standard area: Biological Bases of Behavior

Module 4: The Nervous System and the Endocrine SystemStandard 1: Structure and function of the nervous system in hu-man and non- human animalsModule 4 explores the neuron and its functions. Emphasis is on how neurons communicate with one another. Specific neurotrans-mitters are examined to illustrate how these chemicals affect behavior. The differing roles of sensory, motor, and interneurons are also explained. The divisions of the nervous system are pre-sented along with examples of how these divisions control various types of human behavior.

Standard 2: Structure and function of the endocrine systemThe structures and function of the endocrine system are examined. Emphasis is on the connection between the glandular and neural systems. Focus is on how hormones can influence how we feel and behave.

Module 5: The BrainStandard 3: The interaction between biological factors and experienceModule 5 introduces students to the parts of the brain and their func-tions. The brain is divided into lower- level brain structures and the cerebral cortex. Emphasis is placed on how each structure controls specific behaviors. The author uses the Greek and Latin roots of the words to help students understand how the brain structure func-tions. Module 5 also investigates how the left and right hemispheres influence brain functioning. Emphasis is on language areas in the left hemisphere and spatial abilities in the right. Split- brain research is also presented.

Standard 4: Methods and issues related to biological advancesThe text identifies techniques that allow researchers to analyze brain structures and neural activity. Case studies can illuminate how brain functioning is altered because of injury. The fascinat-ing case of Phineas Gage is presented as an example of this type of research. Also, the author explains how modern technology has allowed researchers to investigate the living brain.

Sensation and Perception

Standard area: Sensation and Perception

Module 6: SensationStandard 1: The processes of sensation and perceptionModule 6 begins with an explanation of “top- down” and “bottom- up” processing to illustrate the differences between sensation and per-ception. The concept of thresholds and sensory adaptation are also introduced as basic principles to understanding our sensory systems. The structures and functioning of the visual and auditory senses are discussed in detail. The senses of taste, smell, touch, kinesthetic, and vestibular are also presented.

Standard 2: The capabilities and limitations of sensory processesThe concept of selective attention is discussed and applied to effec-tive study skills. Signal detection theory is presented in a historical context and illustrated with current applications.

Module 7: PerceptionStandard 3: Interaction of the person and the environment in determining perceptionPerceptual constancy, size, shape, and lightness are explained. Their value in our lives is examined through everyday examples. Module 7 defines and illustrates Gestalt concepts and principles. Emphasis is on figure- ground, similarity, proximity, closure, and continuity. Principles of depth perception, including monocular and binocular depth cues, are explained. The causes of perceiving motion are also explored. The influence of perceptual set and context on perception is discussed. This module concludes by discussing basic perceptual principles that help create illusions.

ConsciousnessStandard area: States of consciousness

Module 8: Sleep, Dreams, and Body RhythmsStandard 1: The relationship between conscious and uncon-scious processesIn Module 8, the author discusses the psychological definition of consciousness. In addition, the biological rhythms that affect our biological functioning are explained. The link between these rhythms and our consciousness is investigated.

Standard 2: Characteristics of sleep and theories that explain why we sleep and dreamModule 8 explores the effects of sleep deprivation on our function-ing. The author also notes the various theories as to why we sleep. In addition, the characteristics of the NREM and REM stages of sleep are explained and compared. The different EEG patterns for the different stages are presented. Common sleep disorders, such as insomnia, sleep apnea, and narcolepsy, are discussed. Other less common sleep disorders, such as somnambulism (sleep walking) and night terrors, are also presented. The four modern explanations of dreaming— information processing, physiological functions, activation synthesis, and cognitive development— are presented. Freud’s theory of dream interpretation is also addressed.

Module 9: Psychoactive DrugsStandard 3: Categories of psychoactive drugs and their effectsModule 9 defines what is meant by a “psychoactive drug” and com-pares the differences among dependence, withdrawal, and tolerance. In addition, four drug categories— depressants, stimulants, halluci-nogens, and marijuana— are presented. Specific drugs, such as alco-hol, are discussed in detail within their specific category. Prevention of drug use is also discussed.

Module 10: Hypnosis and Other States of ConsciousnessStandard 4: Other states of consciousnessModule 10 defines hypnosis and compares the social influence and divided consciousness theories in explaining the phenomenon. Specific hypnotic techniques, including induction, are presented. Hypnotizability is discussed. The author examines if posthypnotic suggestions can lead to lasting behavioral changes, such as los-ing weight. The psychological applications of hypnosis are also addressed, specifically pain control. The author also investigates the controversy surrounding the use of hypnosis to enhance memory recall. In addition, meditation is presented.

Biopsychology


58

DOMAIN 2

inTroduce The domain

Enduring QuestionIn what ways do the biological and psychological processes interact?

Domain Objectives and Essential Questions


Module 4Essential Question: How do the nervous and endocrine systems’ components con-tribute to behavior and mental processes?

objectives

● Identify the parts of the neuron and the function of each.

● Explain the process of neural com-munication in terms of the resting potential, action potential, and refractory period.

● Explain the role of neurotransmit-ters in neural communication.

● Delineate the different steps of the neural chain.

● Identify the components of the ner-vous system, their parts, and their functions.

● Analyze the differences between the endocrine and nervous systems.

Module 5Essential Question: How do the vari-ous parts of the brain work together to create behavior and mental processes?

objectives

● List the tools available to psycholo-gists who want to study the brain.

● Identify the innermost parts of the brain and the function of each.

● Identify the regions of the outer surface of the brain and the function of each.

● Discuss how the hemispheres of the brain are specialized yet work together.

Sensation and Perception

Module 6Essential Question: In what ways are our sensory systems important to our behavior and mental processes?

objectives

● Determine the significance of thresholds, signal detection theory, sensory adaptation, and selective attention in modern psychology.

● Define the nature of light.

nervous-

tribute to behavior and mental processes?

Identify the parts of the neuron and

Analyze the differences between the

surface of the brain and the function

59

Biopsychology

DOMAIN 2

f you wanted to learn about cooking, one way to start would be to learn about kitchens. If you wanted to learn about transportation, one way to start would be to learn about cars. Likewise, to learn about the mind and

behavior, one way to start is to learn about the body. Our biology both enables and limits our ability to behave, think, and feel.

The modules in the biopsychological domain are the “nuts and bolts” of psychology. Our topics— the nervous and endo-crine systems, the brain, sensation, perception, sleep, dreams, body rhythms, psychoactive drugs, hypnosis, and other states of consciousness— all attempt to explain different aspects of how the human “machine” functions. Just as we can partially understand transportation by studying a car, we can partially understand mind and behavior by studying the body.

In the seven modules in the biopsychological domain, we often use two words— stimulus and response. A stimulus is anything you can respond to— the sight of an object, the smell of cooking food, the sound of a friend’s voice, and countless other pieces of your world. A response is simply any action or behavior resulting from a stimulus— saying “Yum” when you smell rhubarb pie baking or turning your head to the sound of your friend’s voice. Your next stimulus is Module 4. We hope you respond positively!

Now buckle up and enjoy the ride as we learn about the relation-ship between biology and psychology.

I

●Biological Bases of Behavior

Module 4 The Nervous System and the Endocrine System

Module 5 The Brain

●Sensation and PerceptionModule 6 Sensation

Module 7 Perception

●ConsciousnessModule 8 Sleep, Dreams, and Body Rhythms

Module 9 Psychoactive Drugs

Module 10 Hypnosis and Other States of Consciousness

● Identify the major components of the visual system and the function of each.● Identify the two theories of color vision and understand why one is considered correct.● Define the nature of sound.● Identify the major components of the auditory system and the function of each.● Explain how tastes, smells, and touch sensations are processed.

Module 7Essential Question: How is perception both consistent and inconsistent among different people?

objectives

● Describe the principles Gestalt psychologists identified that people use to organize the sen-sory world.

● Understand depth perception and its effect on our lives.● Appreciate the value of perceptual constancy in our lives.● Analyze the effect of perceptual set on everyday sensory experiences.● Describe how perceptual principles explain visual illusions.


59

DOMAIN 2

Consciousness

Module 8Essential Question: How does what occurs— or does not occur— during sleep affect daily life?

objectives

● Define consciousness.● Identify the different rhythms of the

body and how they differ from one another.

● Understand why sleep is so impor-tant to daily life.

● Identify the different stages of sleep, including REM and NREM sleep, and analyze their differences.

● Describe the modern explanations for why we dream.

● Identify the different types of sleep disorders and determine the causes and consequences of those disorders on people’s lives.

Module 9Essential Question: How does the use of psychoactive drugs affect people’s lives?

objectives

● Describe a psychoactive drug and what it means to become dependent on one.

● Describe the psychological and physiological effects of consuming alcohol.

● Describe the psychological and physi-ological effects of using stimulants.

● Describe the psychological and physiological effects of using hallucinogens.

● Describe the psychological and physi-ological effects of using marijuana.

● Evaluate what avenues help prevent the use of dangerous psychoactive drugs.

Module 10Essential Question: How are other states of consciousness different from consciousness?

objectives

● Describe how dual process-ing explains different states of consciousness.

● Evaluate whether hypnosis is a dif-ferent state of consciousness.

● Explain what posthypnotic sugges-tions are and how they might be used to help people.

● Evaluate whether hypnosis helps improve memory or control pain.

Consciousness

Module 8Essentialoccurs—affect daily life?

o

●

●

●

●

●

●

Module 9Essentialoflives?

o

●

●

●

●

●

●

Module 10

59

Biopsychology

DOMAIN 2

f you wanted to learn about cooking, one way to start would be to learn about kitchens. If you wanted to learn about transportation, one way to start would be to learn about cars. Likewise, to learn about the mind and

behavior, one way to start is to learn about the body. Our biology both enables and limits our ability to behave, think, and feel.

The modules in the biopsychological domain are the “nuts and bolts” of psychology. Our topics— the nervous and endo-crine systems, the brain, sensation, perception, sleep, dreams, body rhythms, psychoactive drugs, hypnosis, and other states of consciousness— all attempt to explain different aspects of how the human “machine” functions. Just as we can partially understand transportation by studying a car, we can partially understand mind and behavior by studying the body.

In the seven modules in the biopsychological domain, we often use two words— stimulus and response. A stimulus is anything you can respond to— the sight of an object, the smell of cooking food, the sound of a friend’s voice, and countless other pieces of your world. A response is simply any action or behavior resulting from a stimulus— saying “Yum” when you smell rhubarb pie baking or turning your head to the sound of your friend’s voice. Your next stimulus is Module 4. We hope you respond positively!

Now buckle up and enjoy the ride as we learn about the relation-ship between biology and psychology.

I

●Biological Bases of Behavior

Module 4 The Nervous System and the Endocrine System

Module 5 The Brain

●Sensation and PerceptionModule 6 Sensation

Module 7 Perception

●ConsciousnessModule 8 Sleep, Dreams, and Body Rhythms

Module 9 Psychoactive Drugs

Module 10 Hypnosis and Other States of Consciousness

5959595959

transportation by studying a car, we can partially understand mind

In the seven modules in the biopsychological domain, we often is anything you

the sight of an object, the smell of cooking food, the sound of a friend’s voice, and countless other pieces of your

is simply any action or behavior resulting from saying “Yum” when you smell rhubarb pie baking or

turning your head to the sound of your friend’s voice. Your next

Now buckle up and enjoy the ride as we learn about the relation-


4

59a

LeSSon PLanning caLendar

Use this Lesson Planning Calendar to determine how much time to allot for each topic.

Schedule Day One Day Two Day Three Day FourTraditional Period (50 minutes) Neurons: The Building Blocks

of the Nervous SystemHow Neurons Communicate

The Structure of the Nervous System

The Endocrine System

Block Schedule (90 minutes) Neurons: The Building Blocks of the Nervous System

How Neurons Communicate



The Nervous System and the Endocrine System


4

59b

acTiviTy PLanner from The Teacher’S reSource maTeriaLS

Use this Activity Planner to bring active learning to your daily lessons.

Topic Activitiesneurons: The Building Blocks of the nervous System

Getting Started: Critical Thinking Activity: Fact or Falsehood? (20 min.)

Digital Connection: DVD: The Brain and Nervous System: Your Information Highway (25 min.)

Building Vocabulary/Graphic Organizer: The Neuron (20 min.)

Cooperative Learning Activity: The Model Neuron (20 min.)

Digital Connection: Technology Application Activity: Neuroscience and Behavior on the Internet (15 min.)

how neurons communicate Digital Connection: DVD: The Addicted Brain (26 min.)

Digital Connection: Technology Application Activity: The Brain’s Inner Workings (20 min.)

Application Activity: Using Dominoes to Illustrate the Action Potential (20 min.)

Digital Connection: Technology Application Activity: PsychSim: “Neural Messages” (15 min.)

Application Activity: Neural Transmission (20 min.)

Application Activity: Reaction-Time Measure of Neural Transmission and Mental Processes (20 min.)

Enrichment Lesson: Multiple Sclerosis and Guillain-Barré Syndrome (15 min.)

Digital Connection: The Mind (2nd ed.), Module 5: “Endorphins: The Brain’s Natural Morphine” (5 min.)

Digital Connection: The Brain (2nd ed.), Module 30: “Understanding the Brain Through Epilepsy” (12 min.)

Digital Connection: Film: Awakenings (121 min.)

The Structure of the nervous System Digital Connection: DVD: The Brain (28 min.)

Digital Connection: The Autonomic Nervous System (29 min.)

The endocrine System Digital Connection: The Brain (2nd ed.), Module 2: “The Effects of Hormones and the Environment on Brain Development” (15 min.)

Digital Connection: DVD: Endocrine Control: Systems in Balance (30 min.)


60

4

60

P erhaps you’re wondering why you’re reading about the biological bases of behavior. After all, you signed up for a course in psychology, not biology. In the next

two modules, we cover material that looks suspiciously as though it belongs in a biology textbook. What’s going on?

Think of it this way. If your biological being suddenly disappeared, there would be nothing left. Without a body, there could be no behavior, and without a brain, there could be no mental processes. You couldn’t play a sport or a musi-cal instrument. You couldn’t enjoy the taste of a ripe melon or a freshly baked chocolate chip cookie. You couldn’t solve a problem or fantasize about the upcoming weekend. You could neither laugh at a joke (a behavior) nor understand the humor behind it (a mental process). You couldn’t feel anxiety about an upcoming test or fall in love. In a nutshell, if biology disappeared, so would the stuff of psychology.

It’s possible to study behavior and mental processes from a number of perspectives, including the cognitive perspec-tive, the behavioral perspective, and the social- cultural per-spective, and we do that in other sections of this book. But now it’s biology’s turn for the spotlight, and you may be sur-prised at the insight it provides.

4 The Nervous System and the Endocrine System

5 The Brain

MODULES


Your body is an incredible organization of biological systems, each with its own important functions. Your skeletal system supports your body. Your digestive system extracts nutrients from food. Your immune system wards off disease. Your respira-tory system allows you to take in oxygen and rid your cells of carbon dioxide. But the biological systems that psychologists focus on are the nervous system and the endocrine (hormonal) system. These two biological systems enable communication and information processing within our bodies.

Neurons: The Building Blocks of the Nervous System

How Neurons Communicate● The Neural Impulse● Communication

Between Neurons● The Neural Chain




MODULE 4

Have you ever heard of the fight-or-flight response? In a threatening situation, your body instantly prepares you to either fight off the threat or flee to safety. This response is produced by the nervous system and the endocrine system, our topics in this module.

61


61

4inTroduce The moduLe

Getting Started TRMHave students complete Critical Thinking Activity: Fact or False-hood? This prereading strategy evalu-ates what students already know about the neural and hormonal systems. The activity, along with its results, will prime students to note terms and concepts in the text that confirm or dispel their preconceptions about these systems.

Building Vocabulary TRMHave students use Building Vocabulary/Graphic Organizer Activity: The Neuron to learn the module vocabu-lary and identify the parts of the neuron and their functions. Students may complete the activity on their own or in groups. Exceptional learners may wish to work independently or with a tutor. Students may use the textbook as a resource to find answers.

60

P erhaps you’re wondering why you’re reading about the biological bases of behavior. After all, you signed up for a course in psychology, not biology. In the next

two modules, we cover material that looks suspiciously as though it belongs in a biology textbook. What’s going on?

Think of it this way. If your biological being suddenly disappeared, there would be nothing left. Without a body, there could be no behavior, and without a brain, there could be no mental processes. You couldn’t play a sport or a musi-cal instrument. You couldn’t enjoy the taste of a ripe melon or a freshly baked chocolate chip cookie. You couldn’t solve a problem or fantasize about the upcoming weekend. You could neither laugh at a joke (a behavior) nor understand the humor behind it (a mental process). You couldn’t feel anxiety about an upcoming test or fall in love. In a nutshell, if biology disappeared, so would the stuff of psychology.

It’s possible to study behavior and mental processes from a number of perspectives, including the cognitive perspec-tive, the behavioral perspective, and the social- cultural per-spective, and we do that in other sections of this book. But now it’s biology’s turn for the spotlight, and you may be sur-prised at the insight it provides.

4 The Nervous System and the Endocrine System

5 The Brain

MODULES

Biological Bases of BehaviorGetting Started Have students complete Thinkinghood?ates what students already know about the neural and hormonal systems. The activity, along with its results, will prime students to note terms and concepts in the text that confirm or dispel their preconceptions about these systems.

Building Vocabulary Have students use Graphic Organizer Activity: The Neuronlary and identify the parts of the neuron and their functions. Students may complete the activity on their own or in groups. Exceptional learners may wish to work independently or with a tutor. Students may use the textbook as a resource to find answers.

Your body is an incredible organization of biological systems, each with its own important functions. Your skeletal system supports your body. Your digestive system extracts nutrients from food. Your immune system wards off disease. Your respira-tory system allows you to take in oxygen and rid your cells of carbon dioxide. But the biological systems that psychologists focus on are the nervous system and the endocrine (hormonal) system. These two biological systems enable communication and information processing within our bodies.


How Neurons Communicate● The Neural Impulse● Communication

Between Neurons● The Neural Chain




MODULE 4

Have you ever heard of the fight-or-flight response? In a threatening situation, your body instantly prepares you to either fight off the threat or flee to safety. This response is produced by the nervous system and the endocrine system, our topics in this module.

61

The companion website to this book contains teacher resources for class presenta-tions, and concepts and terms for review and assessment. Log on at www.worthpublishers.com/thinkingaboutpsych.

Digital ConneCtion

resource managerActivities TE Web/Multimedia TE Film/Video TEApplication 64, 65 Digital Connection 61, 65, 71 The Brain and Nervous System: Your Information Highway 62

Cooperative Learning 62 Technology Application 63, 65, 68 The Brain (2nd ed.), Module 30 65

Critical Thinking 61 The Mind (2nd ed.), Module 5 66

Enrichment 69 Awakenings 66

Graphic Organizer 61 The Addicted Brain 68

The Autonomic Nervous System 71

The Brain 71

Endocrine Control: Systems in Balance 73

The Brain (2nd ed.), Module 2 74


62

4Teach

Differentiation TRMNeuroglia are a category of neural cells that make up the support net-work surrounding the neurons and blood vessels of the brain and nervous system. They are thought to outnum-ber typical neurons 10 to 1. There are three types of neuroglia:

● Oligodendroglia are found in the central nervous system (CNS). They produce myelin, the protective cov-ering of axons that speeds neural transmissions.

● Schwann cells have the same func-tion as oligodendroglia but are found in the peripheral nervous system (PNS). Unlike oligodendrog-lia, Schwann cells can help axons regenerate.

● Astrocytes are star- shaped and form most of the matrix in which neural cells are embedded. In the brain, astrocytes envelop blood vessels and absorb dead neural cells.

At this point, you may wish to use Cooperative Learning Activity: The Model Neuron and DVD: The Brain and Nervous System: Your Informa-tion Highway.

blood vessels of the brain and nervous

central nervous system (CNS). They

-

-

shaped and form

astrocytes envelop blood vessels and

62 �� B i o p s y c h o l o g y �� Biological Bases of Behavior


WHAT’S THE POINT?

4-1 What are the parts of a neuron, and what do they do?

The nervous system is your body’s electrochemical communication system. Through it, your brain tells your body parts to move, your face to express emotion, and your internal organs to go about their business. Your nervous system, in partnership with your sensory systems, also gathers information so that your brain can respond appropriately to stubbed toes, fire alarms, and the smell of popcorn. Like every other system in your body, your nervous system is built of cells. Looking at those cells is a good starting point for understanding the whole system.

Your brain, spinal cord, and nerves are formed from neurons, the highly specialized and unique nerve cells of the nervous system. A neuron exists only to perform three tasks:

1. To receive information (in the form of electrochemical impulses) from the other neurons that feed into it

2. To carry this information down its length

3. To pass the information on to the next neurons in line

Every behavior, thought, and emotion you’ve ever experienced depends on the neuron’s remarkable ability to process information in these three ways.

The wonder of it all is that neurons are actually quite limited in function— their main capability is simply transmitting an impulse, or “firing.” In some ways, the guts of powerful modern computers operate similarly. A com-

puter’s central processor controls many digital switches that can be either “on” or “off.” All of a computer’s extraordinary capabilities— its communication functions, elaborate games, number crunching, mind- dazzling graphics, and sound— are ulti-mately accomplished by setting switches in the proper on- or- off pattern.

Neurons work in a similar way: They can either fire (that is, send an impulse down their length) or not. That’s it. The beauti-ful colors you see in a sunset, the intense emotions you experience during your first crush, the memory of your first day of kin-dergarten, the taste of pepperoni pizza, the thrill you feel when riding a roller coaster, and the devastating depression someone

neuron A nerve cell; the basic building block of the nervous system.

The Computer and the Brain

Both have amazing capa-bilities and get their power from millions of “switches” (electronic bits in the com-puter, neurons in the brain) that can be either on or off.

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The Nervous System and the Endocrine System �� M o d u l e 4 �� 63

you know may suffer from— all emerge from a certain sequence of neurons either firing or not firing.

Neurons, like trees and dogs, come in a tremendous variety of shapes and sizes, but all neurons have similar structures. Take a minute now to look at Figure 4.1, which shows these structures in a motor neuron, a nerve cell that carries messages to muscles and glands. In this discussion, we examine the neuron’s parts by following the order in which information travels— from the dendrites to the soma, the axon, and the axon terminals.

Dendrites are the branching extensions of a neuron that receive informa-tion and conduct impulses toward the cell body. Dendrites look like branches, and in fact the word dendrite comes from the Greek word for “tree.” From the dendrites, the information moves to the soma, the cell body of a neuron. The soma contains the cell nucleus and other parts that keep the cell healthy and functioning properly. From there, information travels along the axon, the extension of a neuron through which neural impulses are sent. The neu-ron’s purpose is to move information from point A to point B, and the axon creates distance between these points. Axons of neurons in the brain may be very short because information doesn’t have to travel far between the cells. But in some neurons in the leg, axons extend more than 3 feet, making these giant redwoods of the nervous system the longest cells in your body! Longer axons are covered by a myelin sheath that protects the axon and speeds up the transmission of information. Finally, the information reaches the axon terminals, the end point of a neuron where neurotransmitters (discussed soon) are stored. As you will see, axon terminals are the points of departure for information as it makes its way to the dendrites of the next neurons in the sequence.

Pause Now or Move oN

Turn to page 74 to review and apply what you’ve learned.

Dendrites(receive messages from other cells)

Soma (the cell body, which maintains the health of the neuron)

Axon(passes messages away

from the cell body toother neurons,

muscles, or glands)

Myelin sheath(covers the axon of some neurons and helps speedneural impulses)

Neural impulse (action potential) (electrical signal travelingdown the axon)

Terminal branches of axon(form junctions with other cells)

dendrite The branching extensions of a neuron that receive information and conduct impulses toward the cell body (soma).

axon The extension of a neuron through which neural impulses are sent.

axon terminal The end point of a neuron where neurotransmit-ters are stored.

Figure 4.1

A Typical Motor Neuron

Information travels from left to right in this neuron. Messages are received at the dendrites, travel through the soma and down the axon, and arrive at the axon terminals.

The terms nerve and neuron are not interchangeable.

● A neuron is a single cell.● A nerve is a bundle of neurons.

At this point, you may wish to use Cooperative Learning Activ-ity: The Model Neuron.

FYi TRM


63



WHAT’S THE POINT?


The nervous system is your body’s electrochemical communication system. Through it, your brain tells your body parts to move, your face to express emotion, and your internal organs to go about their business. Your nervous system, in partnership with your sensory systems, also gathers information so that your brain can respond appropriately to stubbed toes, fire alarms, and the smell of popcorn. Like every other system in your body, your nervous system is built of cells. Looking at those cells is a good starting point for understanding the whole system.

Your brain, spinal cord, and nerves are formed from neurons, the highly specialized and unique nerve cells of the nervous system. A neuron exists only to perform three tasks:

1. To receive information (in the form of electrochemical impulses) from the other neurons that feed into it

2. To carry this information down its length

3. To pass the information on to the next neurons in line

Every behavior, thought, and emotion you’ve ever experienced depends on the neuron’s remarkable ability to process information in these three ways.

The wonder of it all is that neurons are actually quite limited in function— their main capability is simply transmitting an impulse, or “firing.” In some ways, the guts of powerful modern computers operate similarly. A com-

puter’s central processor controls many digital switches that can be either “on” or “off.” All of a computer’s extraordinary capabilities— its communication functions, elaborate games, number crunching, mind- dazzling graphics, and sound— are ulti-mately accomplished by setting switches in the proper on- or- off pattern.

Neurons work in a similar way: They can either fire (that is, send an impulse down their length) or not. That’s it. The beauti-ful colors you see in a sunset, the intense emotions you experience during your first crush, the memory of your first day of kin-dergarten, the taste of pepperoni pizza, the thrill you feel when riding a roller coaster, and the devastating depression someone

neuron A nerve cell; the basic building block of the nervous system.

The Computer and the Brain

Both have amazing capa-bilities and get their power from millions of “switches” (electronic bits in the com-puter, neurons in the brain) that can be either on or off.

© M

ed

IAp

hO

TOs

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you know may suffer from— all emerge from a certain sequence of neurons either firing or not firing.

Neurons, like trees and dogs, come in a tremendous variety of shapes and sizes, but all neurons have similar structures. Take a minute now to look at Figure 4.1, which shows these structures in a motor neuron, a nerve cell that carries messages to muscles and glands. In this discussion, we examine the neuron’s parts by following the order in which information travels— from the dendrites to the soma, the axon, and the axon terminals.

Dendrites are the branching extensions of a neuron that receive informa-tion and conduct impulses toward the cell body. Dendrites look like branches, and in fact the word dendrite comes from the Greek word for “tree.” From the dendrites, the information moves to the soma, the cell body of a neuron. The soma contains the cell nucleus and other parts that keep the cell healthy and functioning properly. From there, information travels along the axon, the extension of a neuron through which neural impulses are sent. The neu-ron’s purpose is to move information from point A to point B, and the axon creates distance between these points. Axons of neurons in the brain may be very short because information doesn’t have to travel far between the cells. But in some neurons in the leg, axons extend more than 3 feet, making these giant redwoods of the nervous system the longest cells in your body! Longer axons are covered by a myelin sheath that protects the axon and speeds up the transmission of information. Finally, the information reaches the axon terminals, the end point of a neuron where neurotransmitters (discussed soon) are stored. As you will see, axon terminals are the points of departure for information as it makes its way to the dendrites of the next neurons in the sequence.



Dendrites(receive messages from other cells)

Soma (the cell body, which maintains the health of the neuron)

Axon(passes messages away

from the cell body toother neurons,

muscles, or glands)

Myelin sheath(covers the axon of some neurons and helps speedneural impulses)

Neural impulse (action potential) (electrical signal travelingdown the axon)

Terminal branches of axon(form junctions with other cells)

dendrite The branching extensions of a neuron that receive information and conduct impulses toward the cell body (soma).

axon The extension of a neuron through which neural impulses are sent.

axon terminal The end point of a neuron where neurotransmit-ters are stored.

Figure 4.1

A Typical Motor Neuron

Information travels from left to right in this neuron. Messages are received at the dendrites, travel through the soma and down the axon, and arrive at the axon terminals.

Students often wonder why studying biology is important to psychology. Point out that without biology, we have no behavior. Ask: If you could have a brain transplant, whose brain would you choose? Lead a discussion in which students consider how hav-ing a different brain means being a different person. Point out that without our own brains, we aren’t ourselves.

Have students explore this further with Technology Applica-tion Activity: Neuroscience and Behavior on the Internet.

aCtive learning TRM

● Neurons can have unlimited dendrites that connect with several other neurons at once. Most neurons are limited to one axon, however.

● As a neuron’s charge increases, its polarization decreases.

● A neuron at rest has a charge of – 70 millivolts and is fully polarized.

● The action potential kicks off when neurotransmitters polar-ize the neuron.

At this point, you may wish to use Technology Application Activity: PsychSim: “Neural Messages.”

FYi TRM


64

4Differentiation TRM● Ions are particles that carry either

a positive or negative charge. Their movement creates the action potential.

● Matter naturally tends to move from a more crowded to a less crowded area. The neuron is packed with negatively charged ions inside the cell and positively charged ions outside the cell.

● The neuron membrane is normally impermeable, but neurotransmitters weaken it, which allows the ions to move from more crowded to less crowded areas.

At this point, you may wish to use Application Activity: Neural Transmission.

crowded area. The neuron is packed

is normally impermeable, but neurotransmitters


How Neurons CommunicateNow we’re ready to look more closely at what happens when a neuron fires. This involves changes both within a neuron and between neurons.

The Neural Impulse

WHAT’S THE POINT?

4-2 How does a neuron fire?

When a neuron fires, it creates a neural impulse called an action poten-tial. This brief electrical charge works its way from the dendrites to the axon terminals, much as a bite of swallowed food makes its way from your mouth to your stomach. This action potential represents the “on” condition of the neuron. Each action potential is followed by a brief recharging phase known as the refractory period, when a neuron, after firing, cannot gen-erate another action potential. After the refractory period, the neuron is capable of another action potential when it is stimulated. When the cell is recharged, at rest, and capable of generating another action potential, a rest-ing potential exists. Table 4.1 illustrates these steps.

Table 4.1

Three Phases of Communication Within a Neuron

Action potentialThe neural impulse created when a neuron “fires.” The impulse travels from the dendrites down the axon to the axon terminals.

Refractory periodThe brief instant when a new action potential cannot be generated because the neuron is “recharging” after the previous action potential.

Resting potentialThe state of a neuron when it is “charged” but waiting for the next action potential to be generated.

action potential A neural impulse; a brief electrical charge that travels down the axon of a neuron.

resting potential The state of a neuron when it is at rest and capable of generating an action potential.


An interesting fact about how a neuron fires is called the all- or- none princi-ple, which takes its name from the fact that a neuron always fires with the same intensity. All action potentials are the same strength. It doesn’t matter if there is strong stimulation or weak stimulation at the cell’s dendrites. As long as there is enough energy to trigger the neuron, it will fire with the same intensity.

One of the best analogies to a neuron and how it fires is, perhaps unfor-tunately, a toilet. Stop for a moment and think of how a toilet is similar to a neuron. Here are some similarities (perhaps you will be able to think of more):

● Like a neuron, a toilet has an action potential. When you flush, an “impulse” is sent down the sewer pipe.

● Like a neuron, a toilet has a refractory period. There is a short delay after flushing when the toilet cannot be flushed again because the tank is being refilled.

● Like a neuron, a toilet has a resting potential. The toilet is “charged” when there is water in the tank and it is capable of being flushed again.

● Like a neuron, a toilet operates on the all- or- none principle— it always flushes with the same intensity, no matter how much force you apply to the handle (as long as you provide enough force to trigger the mechanism).



Communication Between Neurons

WHAT’S THE POINT?

4-3 What is the role of neurotransmitters in communication between neurons?

So far, we have been discussing how information passes down the length of a single neuron. But how do messages travel from one neuron to the next? Amazingly, this happens without any two neurons actually coming in contact with each other! At every place where an axon terminal of one neuron and the dendrite of an adjacent neuron meet (and there may be thousands of such places on any single neuron), there is a tiny, fluid- filled gap called a syn-apse that action potentials cannot jump. In this gap, chemical messengers known as neurotransmitters travel across the synapse to carry the informa-tion from one neuron to the next. It is the neurotransmitter that influences whether the next neuron will generate an action potential (by firing) or not. When an action potential works its way to the end of a neuron, it causes the release of neurotransmitters from the axon terminals. The neurotransmitter molecules, which have a distinctive chemical shape, rapidly cross the synapse and fit into receptor sites on the dendrite of the next neuron (see Figure 4.2).

The neurotransmitters can come to rest only in receptor sites designed to fit their shape, just as a key can open only certain locks. Once in the receptor

all- or- none principle The prin-ciple stating that if a neuron fires, then it always fires at the same intensity; all action potentials have the same strength.

synapse [SIN- aps] The tiny, fluid- filled gap between the axon terminal of one neuron and the dendrite of another.

neurotransmitter A chemical messenger that travels across the synapse from one neuron to the next and influences whether a neuron will generate an action potential.

Cross- CurriCular ConneCtion

Neural TransmissionMaterials: One bag of Hershey’s Kisses choco-lates; large index cards marked with a “+”

1. Five volunteers act as dendrites and one as a cell body. (Tip: Make sure that students are not allergic to choc-olate or nuts.) Line up another five students behind the first to serve as an axon and two more to act as ter-minal fibers. Repeat this procedure to create a second “neuron.”

2. Scatter “+” cards around each “neuron.” Explain that the cards are positive ions,

the candies are neurotransmitters, and the space between the neurons is the synapse. Give each terminal fiber an unwrapped chocolate to hold.

3. Hand chocolates to the dendrites and cell body. The dendrites and cell body pick up the chocolates and eat them, then immediately pick up a card. When three cards are picked up, the neuron reaches threshold (all- or- none response).

4. At threshold, the first person in the axon picks up a card, and the dendrites and cell body drop theirs. The next “axon

person” picks up a card while the pre-vious one drops his or hers, and so on.

5. When the last person in the axon picks up a card, the terminal fibers toss their chocolates to the dendrites and cell body of the next neuron.

Tip: Use Hershey’s Kisses with differ-ently colored wrappers to show the effects of agonistic and antagonistic drugs. More information is in Application Activity: Neural Transmission and Application Activity: Reaction-Time Measure of Neu-ral Transmission and Mental Processes.

TRM


65

4Differentiation TRMThe sodium- potassium pump is a mechanism that regulates the passage of ions across the cell membrane. The pump brings positively charged ions into the cell, then pumps them back out when the action potential is over. Students interested in learning more about this should check out Technol-ogy Application Activity: PsychSim: “Neural Messages.”

Beyond the Classroom TRMApply One way to explain the all- or- none principle is “There is no such thing as a weak action potential.” That is, the amount of neurotransmitters must reach a threshold level before firing will occur. The charge that results looks no different from any other charge the cell would make. This means that action potentials behave the same way every time. Help stu-dents visualize the all- or- none prin-ciple with Application Activity: Using Dominoes to Illustrate the Action Potential.

Check for Understanding TRMSummarize To evaluate whether students understand how the action potential works, have them write a one- paragraph summary of the pro-cess, using the terms from the text. Answers will vary but should include the following points:

● At its resting potential, the neuron is negatively charged.

● Neurotransmitters from other cells travel across the synapse and bind a neuron, opening channels that then exchange ions and create an elec-trical charge known as the action potential.

● Once the neuron has fired, it must repolarize during a refractory period before it can fire again.

● Enough neurotransmitters must be present for an action potential to take place, demonstrating the all- or- none principle.

At this point, you may wish to use The Brain (2nd ed.), Module 30: “Understanding the Brain Through Epilepsy.”


How Neurons CommunicateNow we’re ready to look more closely at what happens when a neuron fires. This involves changes both within a neuron and between neurons.

The Neural Impulse

WHAT’S THE POINT?


When a neuron fires, it creates a neural impulse called an action poten-tial. This brief electrical charge works its way from the dendrites to the axon terminals, much as a bite of swallowed food makes its way from your mouth to your stomach. This action potential represents the “on” condition of the neuron. Each action potential is followed by a brief recharging phase known as the refractory period, when a neuron, after firing, cannot gen-erate another action potential. After the refractory period, the neuron is capable of another action potential when it is stimulated. When the cell is recharged, at rest, and capable of generating another action potential, a rest-ing potential exists. Table 4.1 illustrates these steps.

Table 4.1

Three Phases of Communication Within a Neuron

Action potentialThe neural impulse created when a neuron “fires.” The impulse travels from the dendrites down the axon to the axon terminals.

Refractory periodThe brief instant when a new action potential cannot be generated because the neuron is “recharging” after the previous action potential.

Resting potentialThe state of a neuron when it is “charged” but waiting for the next action potential to be generated.

action potential A neural impulse; a brief electrical charge that travels down the axon of a neuron.

resting potential The state of a neuron when it is at rest and capable of generating an action potential.

Differentiation The mechanism that regulates the passage of ions across the cell membrane. The pump brings positively charged ions into the cell, then pumps them back out when the action potential is over. Students interested in learning more about this should check out ogy“Neural Messages.”

Beyond the ClassroomApplynone principlething as a weak action potential.” That is, the amount of neurotransmitters must reach a threshold level before firing will occur. The charge that results looks no different from any other charge the cell would make. This means that action potentials behave the same way every time. Help students visualize the all-ciple with Dominoes to Illustrate the Action Potential.

Check for Understanding Summarizestudents understand how the action potential works, have them write a one-cess, using the terms from the text. Answers will vary but should include the following points:

●

●

●

●


An interesting fact about how a neuron fires is called the all- or- none princi-ple, which takes its name from the fact that a neuron always fires with the same intensity. All action potentials are the same strength. It doesn’t matter if there is strong stimulation or weak stimulation at the cell’s dendrites. As long as there is enough energy to trigger the neuron, it will fire with the same intensity.

One of the best analogies to a neuron and how it fires is, perhaps unfor-tunately, a toilet. Stop for a moment and think of how a toilet is similar to a neuron. Here are some similarities (perhaps you will be able to think of more):

● Like a neuron, a toilet has an action potential. When you flush, an “impulse” is sent down the sewer pipe.

● Like a neuron, a toilet has a refractory period. There is a short delay after flushing when the toilet cannot be flushed again because the tank is being refilled.

● Like a neuron, a toilet has a resting potential. The toilet is “charged” when there is water in the tank and it is capable of being flushed again.

● Like a neuron, a toilet operates on the all- or- none principle— it always flushes with the same intensity, no matter how much force you apply to the handle (as long as you provide enough force to trigger the mechanism).




WHAT’S THE POINT?


So far, we have been discussing how information passes down the length of a single neuron. But how do messages travel from one neuron to the next? Amazingly, this happens without any two neurons actually coming in contact with each other! At every place where an axon terminal of one neuron and the dendrite of an adjacent neuron meet (and there may be thousands of such places on any single neuron), there is a tiny, fluid- filled gap called a syn-apse that action potentials cannot jump. In this gap, chemical messengers known as neurotransmitters travel across the synapse to carry the informa-tion from one neuron to the next. It is the neurotransmitter that influences whether the next neuron will generate an action potential (by firing) or not. When an action potential works its way to the end of a neuron, it causes the release of neurotransmitters from the axon terminals. The neurotransmitter molecules, which have a distinctive chemical shape, rapidly cross the synapse and fit into receptor sites on the dendrite of the next neuron (see Figure 4.2).

The neurotransmitters can come to rest only in receptor sites designed to fit their shape, just as a key can open only certain locks. Once in the receptor

all- or- none principle The prin-ciple stating that if a neuron fires, then it always fires at the same intensity; all action potentials have the same strength.

synapse [SIN- aps] The tiny, fluid- filled gap between the axon terminal of one neuron and the dendrite of another.

neurotransmitter A chemical messenger that travels across the synapse from one neuron to the next and influences whether a neuron will generate an action potential.

● Find links to slide presentations and illustrations in the biopsychology animations and tutorials at psychlab1.hanover.edu/Classes/Neuro/.

● A good tutorial of basic neural processes and the human brain can be found on John H. Krantz’s website at psych.hanover.edu/Krantz/neurotut.html. Included are sections on the neuron and the brain, factors involved in the action potential, and a normal brain- structure atlas.

● Students can participate in experiments related to biopsychology at the Online Psychol-ogy Laboratory website (opl.apa.org/Main.aspx), sponsored by the National Science Foundation and the American Psychological Association.

At this point, you may wish to use Technology Application Activity: Neuroscience and Behavior on the Internet.

Digital ConneCtion TRM


66

4Differentiation TRMPoint out that the body has other neurotransmitters in addition to those discussed in this module.

● Substance P is the body’s pain neurotransmitter.

● Endorphins, or endogenous mor-phines, are the body’s natural pain-killers that inhibit Substance P. These are chemically similar to opi-ates, including heroin, codeine, and morphine.

● Norepinephrine is adrenaline found in the central nervous system.

For more information, see The Mind (2nd ed.), Module 5: “Endor-phins: The Brain’s Natural Mor-phine” and Film: Awakenings.

neurotransmitters in addition to those

-ates, including heroin, codeine, and

found in the central nervous system.


site, neurotransmitters can serve two broad functions. Under some circum-stances, neurotransmitters have an excitatory effect, which makes it more likely that the receiving neuron will generate an action potential, or fire. Other times, neurotransmitters have an inhibitory effect, which makes it less likely that the receiving neuron will generate an action potential. The excitatory role is like a green light. It shouts, “Just do it!” The inhibitory role is like a red light. Its message is “Just say no!”

There are dozens of neurotransmitters, although so far researchers have not learned the specific functions of all of them. Different neurotransmit-ters serve different functions, depending not only on the type of receptor site each locks into but also on the place where they are released in the brain (see Thinking Like a Psychological Scientist: Neurotransmitters and Drugs).

The Neural ChainThe neural chain describes the path information follows as it is processed by the nervous system. To understand it, consider the example of playing your favorite radio station on your sound system. What is necessary for this task? First, the radio station must broadcast the music over radio waves. Second, your system’s antenna has to pick up the radio waves and send them as an

Receiving neuron

Sending neuron

1. Electrical impulses (action potentials) traveldown a neuron’s axon until reaching a tiny junctionknown as a synapse.

Sendingneuron

Actionpotential

Axon terminal

NeurotransmitterReceptor sites onreceiving neuron

Synaptic gap

Action potential

2. When an action potential reaches an axon terminal, it stimulates the release of neurotransmitter molecules. These molecules cross the synaptic gap and bind to receptor sites on thereceiving neuron. This allows electrically charged atoms to enter the receiving neuron and excite or inhibit a new action potential.

Synapse

Figure 4.2


The action potential triggers the release of a neurotrans-mitter from the axon terminals of the sending neuron. The neurotransmitter crosses the synapse and locks into receptor sites located on the dendrites of the receiving neuron.


electronic message along a wire to the radio receiver. The receiver must pro-cess this information by tuning to the proper frequency and then filtering and amplifying it. Then the electronic information is sent to the speakers, again along a wire. Finally, the speakers vibrate to create the sound of a new song. The stereo goes through this process of receiving, processing, and outputting information continuously.

Your nervous system also specializes in receiving and processing informa-tion, and it contains functional components similar to those that make up your sound system. First, you need to gather information from your envi-ronment. Your “antennae” are receptor cells, specialized cells in the sen-sory systems of the body. These amazing receptor cells can turn other kinds of energy into action potentials (impulses) your brain can understand. Your eyes, for example, have receptor cells that take light energy and turn it into nerve impulses. Your ears have receptor cells that process sound energy, and elsewhere in your body there are other receptor cells that process smells, tastes, and touch into nerve impulses. Without these receptor cells, your brain would be helpless. By itself, your brain cannot detect light, sound, or smell. Just as you need your sound system to turn radio waves into something meaningful (music), your brain needs your senses and their receptor cells to gather and transform information into a form your brain can understand.

The sense organs are not actually located in the brain, so your nervous system must literally move the information your receptor cells pull in. This movement occurs as billions of neurotransmitter molecules pass messages among millions of these kinds of neurons— from your fingertips, your eyeballs, your ears, your nose, and your mouth to the proper area of the brain for processing. Just as a sound system uses metal wires to move information, your body uses living wires known as nerves, which are bundles of individual neurons. Sensory nerves carry information from the sense receptors to the brain and spinal cord. Without sensory nerves, your brain would be no more effective than your radio receiver would be if somebody cut the wire bringing information from the antenna.

The brain, like a radio receiver, is the real powerhouse of the system. The brain must process a constant barrage of sensory data flowing in from the sen-sory nerves. Your brain receives information about what you see, hear, taste, smell, and feel throughout your body (although most of it is ignored as prob-ably insignificant). It is the brain’s responsibility to deal with all of the infor-mation and make appropriate decisions, just as your sound system properly filters and amplifies an incoming radio signal. The billions of neurons in your brain and spinal cord that process information are called interneurons.

Your brain determines when action is necessary to deal with incoming information. If your brain detects a ball moving toward your head, you need to either catch the ball or duck to avoid being hit. If your brain detects a question asked by your teacher, you need to decide on an appropriate answer and say it. If your brain detects that you’re overheating, you need to begin sweating. The point is that while the brain can determine a course of action on its own (such as speaking or sweating), it cannot actually do these things. To trigger actions the brain must get word to the body’s muscles and glands, just as your sound system must convey the processed signal from the receiver to its speakers. Your sound system uses more wires for this pur-pose. Similarly, your nervous system uses motor nerves to carry information

excitatory effect A neu-rotransmitter effect that makes it more likely that the receiving neuron will generate an action potential, or “fire.”

inhibitory effect A neurotrans-mitter effect that makes it less likely that a receiving neuron will generate an action potential, or “fire.”

receptor cells Specialized cells in every sensory system of the body that can turn other kinds of energy into action potentials (neural impulses) that the brain can process.

sensory nerves Nerves that carry information from the sense receptors to the spinal cord and brain.

interneurons Nerve cells in the brain and spinal cord responsible for processing information.


Computer ScienceArrange for someone knowledgeable in computer programming to make a presentation to the class about binary systems and how they can work. The presenter may be a com-puter teacher, a computer- literate student, or an outside computer programmer familiar with binary systems. Request that the presentation conclude with students attempting to program a computer to perform a simple task using binary code. This activity should help students see that complex behaviors can come from simple patterns.


67

4

ReteachNeural Chain The neural chain, also known as the reflex arc, can be described graphically:

DifferentiationThere are four main types of energy detected by our receptor cells:

● Thermal energy Cells that are sen-sitive to temperature are called ther-moreceptors. Some thermoreceptor cells detect only hot and others only cold; most detect a wide range of temperatures.

● Mechanical energy Cells that are sensitive to pressure are called mechanoreceptors. Examples include ear hair cells, which detect movement of air that sound creates.

● Chemical energy Cells that are sensitive to changes in the chemical environment are called chemorecep-tors. Examples include cells that detect smell and taste.

● Light energy Cells that are sensitive to changes in intensity and hue of light are called photoreceptors. They are found in the rods and cones of the eye.

Teaching TiPSensory and motor neurons are also known as afferent and efferent neu-rons. One way to remember these names is with the acronym SAME: Sensory Afferent, Motor Efferent.


site, neurotransmitters can serve two broad functions. Under some circum-stances, neurotransmitters have an excitatory effect, which makes it more likely that the receiving neuron will generate an action potential, or fire. Other times, neurotransmitters have an inhibitory effect, which makes it less likely that the receiving neuron will generate an action potential. The excitatory role is like a green light. It shouts, “Just do it!” The inhibitory role is like a red light. Its message is “Just say no!”

There are dozens of neurotransmitters, although so far researchers have not learned the specific functions of all of them. Different neurotransmit-ters serve different functions, depending not only on the type of receptor site each locks into but also on the place where they are released in the brain (see Thinking Like a Psychological Scientist: Neurotransmitters and Drugs).

The Neural ChainThe neural chain describes the path information follows as it is processed by the nervous system. To understand it, consider the example of playing your favorite radio station on your sound system. What is necessary for this task? First, the radio station must broadcast the music over radio waves. Second, your system’s antenna has to pick up the radio waves and send them as an

Receiving neuron

Sending neuron

1. Electrical impulses (action potentials) traveldown a neuron’s axon until reaching a tiny junctionknown as a synapse.

Sendingneuron

Actionpotential

Axon terminal

NeurotransmitterReceptor sites onreceiving neuron

Synaptic gap

Action potential

2. When an action potential reaches an axon terminal, it stimulates the release of neurotransmitter molecules. These molecules cross the synaptic gap and bind to receptor sites on thereceiving neuron. This allows electrically charged atoms to enter the receiving neuron and excite or inhibit a new action potential.

Synapse

Figure 4.2


The action potential triggers the release of a neurotrans-mitter from the axon terminals of the sending neuron. The neurotransmitter crosses the synapse and locks into receptor sites located on the dendrites of the receiving neuron.

Reteach

DifferentiationThere are four main types of energy detected by our receptor cells:

●

●

●

●

Teaching TiSensory and motor neurons are also known as afferent and efferent neurons. One way to remember these names is with the acronym S


electronic message along a wire to the radio receiver. The receiver must pro-cess this information by tuning to the proper frequency and then filtering and amplifying it. Then the electronic information is sent to the speakers, again along a wire. Finally, the speakers vibrate to create the sound of a new song. The stereo goes through this process of receiving, processing, and outputting information continuously.

Your nervous system also specializes in receiving and processing informa-tion, and it contains functional components similar to those that make up your sound system. First, you need to gather information from your envi-ronment. Your “antennae” are receptor cells, specialized cells in the sen-sory systems of the body. These amazing receptor cells can turn other kinds of energy into action potentials (impulses) your brain can understand. Your eyes, for example, have receptor cells that take light energy and turn it into nerve impulses. Your ears have receptor cells that process sound energy, and elsewhere in your body there are other receptor cells that process smells, tastes, and touch into nerve impulses. Without these receptor cells, your brain would be helpless. By itself, your brain cannot detect light, sound, or smell. Just as you need your sound system to turn radio waves into something meaningful (music), your brain needs your senses and their receptor cells to gather and transform information into a form your brain can understand.

The sense organs are not actually located in the brain, so your nervous system must literally move the information your receptor cells pull in. This movement occurs as billions of neurotransmitter molecules pass messages among millions of these kinds of neurons— from your fingertips, your eyeballs, your ears, your nose, and your mouth to the proper area of the brain for processing. Just as a sound system uses metal wires to move information, your body uses living wires known as nerves, which are bundles of individual neurons. Sensory nerves carry information from the sense receptors to the brain and spinal cord. Without sensory nerves, your brain would be no more effective than your radio receiver would be if somebody cut the wire bringing information from the antenna.

The brain, like a radio receiver, is the real powerhouse of the system. The brain must process a constant barrage of sensory data flowing in from the sen-sory nerves. Your brain receives information about what you see, hear, taste, smell, and feel throughout your body (although most of it is ignored as prob-ably insignificant). It is the brain’s responsibility to deal with all of the infor-mation and make appropriate decisions, just as your sound system properly filters and amplifies an incoming radio signal. The billions of neurons in your brain and spinal cord that process information are called interneurons.

Your brain determines when action is necessary to deal with incoming information. If your brain detects a ball moving toward your head, you need to either catch the ball or duck to avoid being hit. If your brain detects a question asked by your teacher, you need to decide on an appropriate answer and say it. If your brain detects that you’re overheating, you need to begin sweating. The point is that while the brain can determine a course of action on its own (such as speaking or sweating), it cannot actually do these things. To trigger actions the brain must get word to the body’s muscles and glands, just as your sound system must convey the processed signal from the receiver to its speakers. Your sound system uses more wires for this pur-pose. Similarly, your nervous system uses motor nerves to carry information

excitatory effect A neu-rotransmitter effect that makes it more likely that the receiving neuron will generate an action potential, or “fire.”

inhibitory effect A neurotrans-mitter effect that makes it less likely that a receiving neuron will generate an action potential, or “fire.”

receptor cells Specialized cells in every sensory system of the body that can turn other kinds of energy into action potentials (neural impulses) that the brain can process.

sensory nerves Nerves that carry information from the sense receptors to the spinal cord and brain.

interneurons Nerve cells in the brain and spinal cord responsible for processing information.

Sensory information enters the body through

receptor cells.

The brain processesthe sensory info anddecides what to do.

Motor nervesreceive commands from

the brain and react.


68

4

Differentiation TRMWhen substances enter the blood-stream, they are carried to all parts of the body. However, many substances are blocked from reaching the brain by the blood- brain barrier (BBB). This specialized membrane selectively pre-vents harmful substances from reach-ing the brain while allowing nutrients and other useful substances to cross.

● One criterion for this selectivity is molecular size: Large molecules are denied entry. This sometimes blocks helpful substances from entering the brain.

● However, the smaller precursors of large molecules can pass through the BBB. Once inside the brain, the precursors are converted to the use-ful chemical.

● A good example of this action is seen in Parkinson’s patients who need dopamine to alleviate their symptoms. Because dopamine cannot cross the BBB, patients take a dopamine pre-cursor called L- dopa, which is con-verted into dopamine inside the brain.

At this point, you may wish to use Technology Application Activity: The Brain’s Inner Workings.

are blocked from reaching the brain by

molecular size: Large molecules are denied entry. This sometimes blocks helpful substances from entering the

-

dopamine to alleviate their symptoms.

verted into dopamine inside the brain.

Activity: The


The synapse is where it’s at when it comes to the effects of many drugs. Let’s take a look at the roles of three key neurotransmitters (see Table 4.2) and see what hap-pens when outside chemicals are added to the mix.

One neurotransmitter, acetylcholine (ACh), trig-gers muscle contraction and affects both learning and memory (Alzheimer’s disease is associated with low levels of ACh). ACh is present in every synapse of motor nerves. Certain drugs can disrupt the normal effects of ACh, however. Some South American Indi-ans use such a drug, a poison called curare, to coat the tips of the darts they use in their blowguns. When these darts strike an animal, the result is paralysis. Why? Because the curare molecules fill the receptor sites on dendrites that normally receive ACh, but the curare molecules do not stimulate an action potential in the receiving neuron the way ACh would. This means that ACh is blocked from doing its job, and movement ceases. Substances such as curare that block the effects of a neurotransmitter are called antagonists.

Black widow spider venom also interacts with ACh, but not in the same way curare does. The venom fills

the ACh receptor sites, but its chemical structure is so similar to ACh that it mimics ACh’s effect on the receiving neuron. So, now two substances, ACh and spider venom, are doing the same thing. The result is excessive and uncontrollable movement in the form of convulsions. The spider venom is called an agonist, a drug that boosts the effect of a neurotransmitter. Fig-ure 4.3 illustrates how antagonists and agonists inter-act with neurotransmitters.

Another neurotransmitter with interesting effects is dopamine, which influences learning, attention, and emotion. Schizophrenia, a serious illness that dis-rupts a person’s sense of reality, is associated with high levels of dopamine. Drugs commonly prescribed for schizophrenia alleviate some of the symptoms by blocking the action of dopamine at the synapse. These drugs are dopamine antagonists.

Another disorder, depression, may be associated with low levels of the neurotransmitter serotonin, which affects hunger, sleep, arousal, and mood. Some medications, the most famous of which is Prozac, work to reduce depression by enhancing the availability of

Neurotransmitters and Drugs

Thinking Like a P S Y C H O L O G I C A L S C I E N T I S T

Table 4.2

Examples of Neurotransmitter Functions

Neurotransmitter Affected Functions Associated Problems

Acetylcholine (ACh) • Muscle action

• Learning

• Memory

ACh- producing neurons have deteriorated in people with Alzheimer’s disease.

Dopamine • Learning

• Attention

• Emotion

Excess dopamine activity is associated with schizophrenia.

Serotonin • Hunger

• Sleep

• Arousal

• Mood

Low levels of serotonin may be associated with depression.


This neurotransmitter molecule fits the receptor site on the receiving neuron, much as a key fits a lock.

This agonist molecule excites. It is similar enough in structure to the neurotransmitter molecule to mimic its effects on the receiving neuron. Black widow spider venom, for instance, mimics the action of ACh by stimulating receptors in brain areas involved in movement, causing convulsions.

This antagonist moleculeinhibits. It has a structuresimilar enough to the neurotransmitter to occupy its receptor site and block its action, but not similar enough to stimulate the receptor. Curare poisoning paralyzes its victims by blocking ACh receptors involved in muscle movement.

Receiving cell membrane

Neurotransmitter molecule

Receptor site on receiving neuron

Agonist mimics neurotransmitter

Antagonist blocks neurotransmitter

(a)

(b)

(c)

Synapticgap

Receptorsites

Receiving neuron

Neurotransmittermolecule

Actionpotential

Sendingneuron

Neurotransmitters carry a message from asending neuron across a synapse to receptorsites on a receiving neuron.

serotonin at the synapse. Prozac, therefore, is a sero-tonin agonist.

Prescribed medications are not the only sub-stances that exert their effects at the synapse. All mind- altering chemicals, ranging from caffeine to cocaine, operate by influencing neurotransmission. A single drug, such as alcohol, might influence several neurotransmitters in different ways depending on the synapse it enters. Research on neurotransmitters is always in progress and brings fascinating and impor-tant results.

antagonist A drug that blocks the effect of a neurotransmitter.

agonist A drug that boosts the effect of a neurotransmitter.

Figure 4.3

Antagonists and Agonists

When a drug blocks the effect of a neurotransmitter, it’s called an antagonist. When a drug boosts the effect of a neurotransmitter, it’s called an agonist.

Patients who take dopamine inhibitors to treat schizophrenia often experience tardive dyki-nesia, a side effect that produces symptoms similar to those of Parkinson’s disease: shaking, twitching, and repetitive move-ments. This effect helped reveal that schizophrenia and Parkin-son’s disease are both related to dopamine levels in the brain.

FYi


LiteratureAntagonist is a term used in literature to identify the character who is fighting against the main character or hero. Have students use this knowledge to enhance their recall of this term in biopsychology.

● The antagonist molecule works against the neurotransmitter by keeping the neuron from firing, much like the antagonist in literature works against the hero, blocking his or her actions.

● In contrast, an agonist molecule works with the neurotransmitter, acting like it just enough to make the neuron fire.

● For drugs to have an effect, there must be a receptor site on a cell that “fits” the drug’s struc-ture, much like a key fits a lock.

● The drugs we take are similar in structure and effect to sub-stances naturally produced by our bodies. By taking a drug, we are either increasing the effect of these natural sub-stances or blocking their action for therapeutic reasons.

At this point, you may wish to watch The Addicted Brain.

FYi TRM


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4Beyond the ClassroomResearch Have students research myasthenia gravis, a neurological disorder resulting from the depletion of acetylcholine (ACh). Without nor-mal levels of ACh, the muscles will not move properly. People with myasthe-nia gravis experience extreme fatigue, because it takes an enormous effort to move the muscles even slightly without help from ACh.

Teaching TiPExplain that reuptake is the body’s way of recycling neurotransmitters for later use. Drugs like Prozac block the reuptake of the neurotransmitter serotonin so it will remain in the syn-apse longer, elevating the mood that serotonin controls.

DifferentiationThe word endorphin was coined from “endogenous morphine” and refers to the brain’s natural painkillers, or opiates. (The drug morphine is a derivative of opium.) Endorphins are produced by the brain, the pituitary gland, and other tissues in response to pain and stress.

● Studies of laboratory rats have dem-onstrated that undergoing shock— even anticipating it— can increase brain endorphin secretion. When rats were placed in a chamber where they had been shocked a week ear-lier, the level of the brain’s natural opiates immediately increased.

● Strenuous, vigorous exercise may also trigger endorphin release. Dur-ing a long, difficult workout, the nervous system can dip into its endorphin reserve and block pain messages— thus producing the so- called runner’s high.


The synapse is where it’s at when it comes to the effects of many drugs. Let’s take a look at the roles of three key neurotransmitters (see Table 4.2) and see what hap-pens when outside chemicals are added to the mix.

One neurotransmitter, acetylcholine (ACh), trig-gers muscle contraction and affects both learning and memory (Alzheimer’s disease is associated with low levels of ACh). ACh is present in every synapse of motor nerves. Certain drugs can disrupt the normal effects of ACh, however. Some South American Indi-ans use such a drug, a poison called curare, to coat the tips of the darts they use in their blowguns. When these darts strike an animal, the result is paralysis. Why? Because the curare molecules fill the receptor sites on dendrites that normally receive ACh, but the curare molecules do not stimulate an action potential in the receiving neuron the way ACh would. This means that ACh is blocked from doing its job, and movement ceases. Substances such as curare that block the effects of a neurotransmitter are called antagonists.

Black widow spider venom also interacts with ACh, but not in the same way curare does. The venom fills

the ACh receptor sites, but its chemical structure is so similar to ACh that it mimics ACh’s effect on the receiving neuron. So, now two substances, ACh and spider venom, are doing the same thing. The result is excessive and uncontrollable movement in the form of convulsions. The spider venom is called an agonist, a drug that boosts the effect of a neurotransmitter. Fig-ure 4.3 illustrates how antagonists and agonists inter-act with neurotransmitters.

Another neurotransmitter with interesting effects is dopamine, which influences learning, attention, and emotion. Schizophrenia, a serious illness that dis-rupts a person’s sense of reality, is associated with high levels of dopamine. Drugs commonly prescribed for schizophrenia alleviate some of the symptoms by blocking the action of dopamine at the synapse. These drugs are dopamine antagonists.

Another disorder, depression, may be associated with low levels of the neurotransmitter serotonin, which affects hunger, sleep, arousal, and mood. Some medications, the most famous of which is Prozac, work to reduce depression by enhancing the availability of

Neurotransmitters and Drugs

Thinking Like a P S Y C H O L O G I C A L S C I E N T I S T

Table 4.2

Examples of Neurotransmitter Functions

Neurotransmitter Affected Functions Associated Problems

Acetylcholine (ACh) • Muscle action

• Learning

• Memory

ACh- producing neurons have deteriorated in people with Alzheimer’s disease.

Dopamine • Learning

• Attention

• Emotion

Excess dopamine activity is associated with schizophrenia.

Serotonin • Hunger

• Sleep

• Arousal

• Mood

Low levels of serotonin may be associated with depression.

Beyond the ClassroomResearchmyastheniadisorder resulting from the depletion of mal levels of ACh, the muscles will not move properly. People with myasthenia gravis experience extreme fatigue, because it takes an enormous effort to move the muscles even slightly without help from ACh.

Teaching TiExplain that way of recycling neurotransmitters for later use. Drugs like Prozac block the reuptake of the neurotransmitter serotonin so it will remain in the synapse longer, elevating the mood that serotonin controls.

DifferentiationThe word “endogenous morphine” and refers to the brain’s natural painkillers, or opiates. (The drug morphine is a derivative of opium.) Endorphins are produced by the brain, the pituitary gland, and other tissues in response to pain and stress.

●

●


This neurotransmitter molecule fits the receptor site on the receiving neuron, much as a key fits a lock.

This agonist molecule excites. It is similar enough in structure to the neurotransmitter molecule to mimic its effects on the receiving neuron. Black widow spider venom, for instance, mimics the action of ACh by stimulating receptors in brain areas involved in movement, causing convulsions.

This antagonist moleculeinhibits. It has a structuresimilar enough to the neurotransmitter to occupy its receptor site and block its action, but not similar enough to stimulate the receptor. Curare poisoning paralyzes its victims by blocking ACh receptors involved in muscle movement.

Receiving cell membrane

Neurotransmitter molecule

Receptor site on receiving neuron

Agonist mimics neurotransmitter

Antagonist blocks neurotransmitter

(a)

(b)

(c)

Synapticgap

Receptorsites

Receiving neuron

Neurotransmittermolecule

Actionpotential

Sendingneuron

Neurotransmitters carry a message from asending neuron across a synapse to receptorsites on a receiving neuron.

serotonin at the synapse. Prozac, therefore, is a sero-tonin agonist.

Prescribed medications are not the only sub-stances that exert their effects at the synapse. All mind- altering chemicals, ranging from caffeine to cocaine, operate by influencing neurotransmission. A single drug, such as alcohol, might influence several neurotransmitters in different ways depending on the synapse it enters. Research on neurotransmitters is always in progress and brings fascinating and impor-tant results.

antagonist A drug that blocks the effect of a neurotransmitter.

agonist A drug that boosts the effect of a neurotransmitter.

Figure 4.3

Antagonists and Agonists

When a drug blocks the effect of a neurotransmitter, it’s called an antagonist. When a drug boosts the effect of a neurotransmitter, it’s called an agonist.

Neurological DisordersHave students research neurologi-cal disorders that aren’t included in the text. Some significant neurological disorders students might research include multiple sclerosis (MS), Guillain- Barré syndrome, Parkinson’s disease, and Lou Gehrig’s disease (ALS). As a starting point, students can review Enrichment Lesson: Multiple Sclerosis and Guillain- Barré Syndrome

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4DifferentiationHave you ever jerked away from a hot surface only to feel the burn after a delay? Interneurons make this reflex happen. These cells in the spinal cord process motor responses quickly to protect the body from harm. Without interneurons, you would not remove your hand from that hot surface soon enough to prevent severe burns.

Check for UnderstandingThis activity will help you see if students understand the process of reflexes and the neural chain.

● Have students brainstorm stimuli that would produce reflexive responses. (Answers will vary but might include responses to heat, cold, pressure, or loud noise.)

● Have them explain why the reflexive response is important to protect the body. (Quick reflexes protect the body from burns, frostbite, insect bites, ear damage, and similar dangers.)

● Finally, have them describe a situation that would require deeper processing by the brain. (Deeper pro-cessing could produce feelings of fear of the stimulus, relief for avoiding more danger, or more complex feel-ings of pain.)

might include responses to heat, cold,

Have them explain why the reflexive response is important to protect the

(Quick reflexes protect the body from burns, frostbite, insect bites, ear

(Deeper pro-cessing could produce feelings of fear


away from your brain and spinal cord to your muscles and glands so that they can take action. Without motor nerves, your brain could not accom-plish anything. (Your sound system wouldn’t be much good without speak-ers, would it?)

Figure 4.4 shows a neural chain so basic that the initial action is determined by the spinal cord without the involvement of the brain. In this case, the response to the heat from the flame is a simple reflex. To react quickly to a dangerous situ-ation, an interneuron in the spinal cord sends the command to withdraw the finger even before other interneurons relay the information to your brain.



The Structure of the Nervous SystemWHAT’S THE POINT?

4-4 What are the divisions of the nervous system, and what do they do?

So far, we’ve examined the nervous system by zooming in on its smaller pieces— sensory and motor nerves made up of bundles of neurons that send their neu-rotransmitters to one another. Now it’s time to take a step back for a broader view of the whole nervous system in which these smaller pieces function.

Brain

Muscle

1. Skin receptorsSkin receptors detect the heat of the flame and generate nerveimpulses. The information travels along a sensory nerve (shown by the large red arrow).

4. Motor nerves(outgoing information) Motor nerves (blue) carry the command to the muscles to withdraw the finger.

2. Sensory nerves(incoming information)Sensory nerves (red) carry the information to the spinal cord.

Spinal cord

3. InterneuronsInterneurons inthe brain and spinal cord processthe information.

Because this reflex involves only the spinal cord, the hand jerks away from the candle flame even before information about the event has reached the brain.

Figure 4.4

A Neural Chain

When you burn your finger, a neural chain is activated. Receptor cells, sensory nerves, interneurons, motor nerves, and muscles all work together to minimize the damage from the flame.


One good way to understand the nervous system is to study its major divi-sions, which you can see in Figure 4.5. The nervous system has two major components: the central nervous system and the peripheral nervous system.

The central nervous system (CNS) includes the brain and the spinal cord, both of which are so important that they are encased in bone for protection. The brain is where most information processing takes place, and the spinal cord is the main pathway information follows as it enters and leaves the brain. In shape, the spinal cord tapers from about the thickness of a broomstick where it joins the brain to the diameter of a pencil lead at the base of the back. The interneurons that make up the CNS are responsible for processing information.

The peripheral nervous system (PNS) contains all sensory nerves and motor nerves that connect the brain and the spinal cord to the rest of the body. The word peripheral means “outer region” (perhaps you’ve heard of periph-eral vision, which refers to your ability to see things on the outer regions of your visual field). The PNS divides into two subsystems— the somatic ner-vous system and the autonomic nervous system:

● The somatic nervous system is the division of the peripheral nervous sys-tem that controls the body’s skeletal muscles. It contains the motor nerves you use to activate muscles voluntarily. You develop the idea to walk across a room using your central nervous system, but you rely on your somatic nervous system to carry the CNS’s commands to the muscles of your legs and to get feedback about what your legs are actually doing.

● The autonomic nervous system is the division of the peripheral nervous system that controls the glands and muscles of the internal organs. It monitors the automatic functions of your body. Your auto-nomic nervous system controls your breathing, blood pressure, and digestive processes.

Nervoussystem

PeripheralCentral

(brain and spinal cord)

Autonomic (controlsself-regulated action of

internal organs and glands)

Somatic (controlsvoluntary movements of

skeletal muscles)

Sympathetic(arousing)

Parasympathetic(calming)

Peripheral nervous system (orange)

Central nervous system (green)

●did you notice that this is the second time in this module we have a word built from the Greek soma, which means “body”?

central nervous system (CNS) The brain and the spinal cord.

peripheral nervous system (PNS) The sensory and motor nerves that connect the brain and the spinal cord to the rest of the body.

somatic nervous system The division of the peripheral nervous system that controls the body’s skeletal muscles.

autonomic [aw- tuh- NAHM- ik] nervous system The division of the peripheral nervous system that controls the glands and muscles of the internal organs; its subdivisions are the sympa-thetic (arousing) division and the parasympathetic (calming) division.

Figure 4.5

Divisions of the Nervous System

The nervous system is made up of several important divisions.

Body Magic and Neural Communication

1. Hold a dollar bill between the middle finger and thumb of your dominant hand. At the same time, the index finger and thumb of your other hand are placed on either side of the note at its center, as close as possible without actually touching it. Release the bill, and you will have no problem catching it.

2. Hold the note as before but instruct a second person to position his or her own fin-ger and thumb as you did earlier for the catching. Drop it, and surprisingly, his or her fingers will close on thin air. Slightly more time is necessary for the other person to process both the visual information and the reaction, showing how neural com-munication and behavior are related.

Source: Fisher, J. (1979). Body magic. New York, NY: Stein & Day.

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71


away from your brain and spinal cord to your muscles and glands so that they can take action. Without motor nerves, your brain could not accom-plish anything. (Your sound system wouldn’t be much good without speak-ers, would it?)

Figure 4.4 shows a neural chain so basic that the initial action is determined by the spinal cord without the involvement of the brain. In this case, the response to the heat from the flame is a simple reflex. To react quickly to a dangerous situ-ation, an interneuron in the spinal cord sends the command to withdraw the finger even before other interneurons relay the information to your brain.



The Structure of the Nervous SystemWHAT’S THE POINT?


So far, we’ve examined the nervous system by zooming in on its smaller pieces— sensory and motor nerves made up of bundles of neurons that send their neu-rotransmitters to one another. Now it’s time to take a step back for a broader view of the whole nervous system in which these smaller pieces function.

Brain

Muscle

1. Skin receptorsSkin receptors detect the heat of the flame and generate nerveimpulses. The information travels along a sensory nerve (shown by the large red arrow).

4. Motor nerves(outgoing information) Motor nerves (blue) carry the command to the muscles to withdraw the finger.

2. Sensory nerves(incoming information)Sensory nerves (red) carry the information to the spinal cord.

Spinal cord

3. InterneuronsInterneurons inthe brain and spinal cord processthe information.

Because this reflex involves only the spinal cord, the hand jerks away from the candle flame even before information about the event has reached the brain.

Figure 4.4

A Neural Chain

When you burn your finger, a neural chain is activated. Receptor cells, sensory nerves, interneurons, motor nerves, and muscles all work together to minimize the damage from the flame.


One good way to understand the nervous system is to study its major divi-sions, which you can see in Figure 4.5. The nervous system has two major components: the central nervous system and the peripheral nervous system.

The central nervous system (CNS) includes the brain and the spinal cord, both of which are so important that they are encased in bone for protection. The brain is where most information processing takes place, and the spinal cord is the main pathway information follows as it enters and leaves the brain. In shape, the spinal cord tapers from about the thickness of a broomstick where it joins the brain to the diameter of a pencil lead at the base of the back. The interneurons that make up the CNS are responsible for processing information.

The peripheral nervous system (PNS) contains all sensory nerves and motor nerves that connect the brain and the spinal cord to the rest of the body. The word peripheral means “outer region” (perhaps you’ve heard of periph-eral vision, which refers to your ability to see things on the outer regions of your visual field). The PNS divides into two subsystems— the somatic ner-vous system and the autonomic nervous system:

● The somatic nervous system is the division of the peripheral nervous sys-tem that controls the body’s skeletal muscles. It contains the motor nerves you use to activate muscles voluntarily. You develop the idea to walk across a room using your central nervous system, but you rely on your somatic nervous system to carry the CNS’s commands to the muscles of your legs and to get feedback about what your legs are actually doing.

● The autonomic nervous system is the division of the peripheral nervous system that controls the glands and muscles of the internal organs. It monitors the automatic functions of your body. Your auto-nomic nervous system controls your breathing, blood pressure, and digestive processes.

Nervoussystem

PeripheralCentral

(brain and spinal cord)

Autonomic (controlsself-regulated action of

internal organs and glands)

Somatic (controlsvoluntary movements of

skeletal muscles)

Sympathetic(arousing)

Parasympathetic(calming)

Peripheral nervous system (orange)

Central nervous system (green)

●did you notice that this is the second time in this module we have a word built from the Greek soma, which means “body”?

central nervous system (CNS) The brain and the spinal cord.

peripheral nervous system (PNS) The sensory and motor nerves that connect the brain and the spinal cord to the rest of the body.

somatic nervous system The division of the peripheral nervous system that controls the body’s skeletal muscles.

autonomic [aw- tuh- NAHM- ik] nervous system The division of the peripheral nervous system that controls the glands and muscles of the internal organs; its subdivisions are the sympa-thetic (arousing) division and the parasympathetic (calming) division.

Figure 4.5

Divisions of the Nervous System

The nervous system is made up of several important divisions.

Updates on the most recent research on spinal cord repair can be found at www.spinal-research.org.

Digital ConneCtion

In 1996, Henrich Cheng and colleagues from the Karolinska Institute in Stockholm, Sweden, were the first to demonstrate that a spinal cord can repair itself, giving new hope to thousands of paralyzed people.

FYi

● Sensory neurons connect to the spinal cord dorsally, or in the back.

● Motor neurons connect in the anterior of the spinal cord, or in the front.

Therefore, it is possible to lose feeling in lower portions of the body in a spinal cord injury but retain the ability to move if the dorsal region of the spinal cord is injured but not completely severed.

At this point, you may want to use the video resources The Auto-nomic Nervous System and The Brain.

FYi TRM


72

4

ReteachPeripheral Nervous System Present the following graphic, which shows the organization of the peripheral nervous system.

Teaching TiPMany of the body’s functions are con-trolled by opposing processes like the parasympathetic and sympathetic nervous systems. These processes work in opposition to create a steady state, or homeostasis, in the body.


The autonomic nervous system has two subdivisions— a sympathetic division and a parasympathetic division (see Figure 4.6). These two divi-sions work together in a masterful example of checks and balances— it’s not just our government that relies on this principle! The sympathetic division is the part of the autonomic nervous system that arouses the body to deal with perceived threats. It controls a number of responses collectively referred to as the fight- or- flight response. If you hear footsteps closing in behind you late at night on a deserted sidewalk, if a teacher announces a pop quiz at the beginning of class, or if you’re about to make a nervous phone call to ask somebody out on a date, then your sympa-thetic nervous system will kick in.

The parasympathetic division is the part of the autonomic nervous sys-tem that calms the body. The sympathetic division may send your blood pressure higher when you are caught coming in after your curfew; your para-sympathetic division brings your blood pressure back down to normal when your explanation of car trouble is fortunately accepted.

SYMPATHETICNERVOUS SYSTEM

(arousing)

PARASYMPATHETICNERVOUS SYSTEM

(calming)Brain

Dilatespupil

Contractspupil

Slowsheartbeat

Spinalcord

Stimulatesdigestion

Stimulatesgallbladder

Contractsbladder

HeartAcceleratesheartbeat

Stomach Inhibitsdigestion

Pancreas

Liver

Adrenalgland

Kidney

Relaxesbladder

Stimulatessecretion ofepinephrine,norepinephrine

Stimulatesglucosereleaseby liver

sympathetic division The part of the autonomic nervous system that arouses the body to deal with perceived threats.

parasympathetic division The part of the autonomic nervous system that calms the body.



Figure 4.6

The Sympathetic and Parasympathetic Divisions of the Autonomic Nervous System

The sympathetic division arouses us and expends energy. The parasympa-thetic division calms us and conserves energy.


The Endocrine SystemWHAT’S THE POINT?

4-5 How does the endocrine system communicate, and what does it do within the body?

Besides the nervous system, your body has another system for communicat-ing information. This system, slower to awaken and slower to shut down than the nervous system, is the endocrine system, a set of glands that produce hormones. Hormones are chemical messengers that circulate throughout the body in the blood. Hormones and neurotransmitters are similar in function: Both carry messages, and both communicate by locking into receptor sites.

Figure 4.7 illustrates the major endocrine glands. The most important is the pituitary gland, the endocrine system’s “master gland.” The pituitary gland, in conjunction with an adjacent brain area, controls the other endocrine glands. The brain may call on the pituitary to release hormones that stimu-late or inhibit the release of other hormones from other endocrine glands. The pea- sized pituitary is located at the base of the brain, and it connects to a part of the brain called the hypothalamus. At this connection, the tis-sue is part glandular and part neural, which illustrates the close relationship between the nervous and the endocrine systems.

The brain monitors the levels of hormones circulating in the blood and may be influenced by their levels. Hunger, for example, is a response to a complex inter-action of the nervous system and the endocrine system. The hypothalamus and pituitary gland work together to monitor and control the levels of glucose (blood

Hypothalamus(brain region controlling

the pituitary gland)

Thyroid gland(affects metabolism,among other things)

Pituitary gland(secretes many different hormones, some of which affect other glands)

Adrenal glands(inner part helps

trigger the“fight-or-flight”

response) Pancreas(regulates the level of sugar in the blood)

Ovary(secretes femalesex hormones)

Testis(secretes male sex

hormones)

endocrine [EN- duh- krin] system One of the body’s two communication systems; a set of glands that produce hormones, chemical messengers that circu-late in the blood.

hormone A chemical messen-ger produced by the endocrine glands and circulated in the blood.

pituitary gland The endocrine system’s “master gland” that, in conjunction with an adjacent brain area, controls the other endocrine glands.

Figure 4.7

Major Glands of the Endocrine System

Endocrine glands secrete hormones into the blood-stream. The hormones can influence how we feel and behave.

Unlike central nerves, peripheral nerves, which extend to the body’s extremities, can regenerate when damaged.

FYi

Sympathetic nervous system arouses the body in response to the stress

Somatic nervous system controls voluntary movements

Parasympathetic nervous system returns the body to homeostasis after stress

Autonomic nervous system controls involuntary movements

Peripheral Nervous System (PNS)


73

4Teaching TiP TRMThe Greek root endo- means “to the inside.” Endocrine glands secrete hor-mones directly into the bloodstream. These are then carried to target organs.

In contrast, exocrine glands secrete substances through ducts and therefore outside the bloodstream. The Greek root exo- means “to the outside.” Salivary glands, tear glands, and sweat glands are examples of exocrine glands.

At this point, you may want to watch Endocrine Control: Systems in Balance.


The autonomic nervous system has two subdivisions— a sympathetic division and a parasympathetic division (see Figure 4.6). These two divi-sions work together in a masterful example of checks and balances— it’s not just our government that relies on this principle! The sympathetic division is the part of the autonomic nervous system that arouses the body to deal with perceived threats. It controls a number of responses collectively referred to as the fight- or- flight response. If you hear footsteps closing in behind you late at night on a deserted sidewalk, if a teacher announces a pop quiz at the beginning of class, or if you’re about to make a nervous phone call to ask somebody out on a date, then your sympa-thetic nervous system will kick in.

The parasympathetic division is the part of the autonomic nervous sys-tem that calms the body. The sympathetic division may send your blood pressure higher when you are caught coming in after your curfew; your para-sympathetic division brings your blood pressure back down to normal when your explanation of car trouble is fortunately accepted.

SYMPATHETICNERVOUS SYSTEM

(arousing)

PARASYMPATHETICNERVOUS SYSTEM

(calming)Brain

Dilatespupil

Contractspupil

Slowsheartbeat

Spinalcord

Stimulatesdigestion

Stimulatesgallbladder

Contractsbladder

HeartAcceleratesheartbeat

Stomach Inhibitsdigestion

Pancreas

Liver

Adrenalgland

Kidney

Relaxesbladder

Stimulatessecretion ofepinephrine,norepinephrine

Stimulatesglucosereleaseby liver

sympathetic division The part of the autonomic nervous system that arouses the body to deal with perceived threats.

parasympathetic division The part of the autonomic nervous system that calms the body.



Figure 4.6

The Sympathetic and Parasympathetic Divisions of the Autonomic Nervous System

The sympathetic division arouses us and expends energy. The parasympa-thetic division calms us and conserves energy.

Teaching TiThe Greek root inside.” mones directly into the bloodstream. These are then carried to target organs.

secrete substances through ducts and therefore outside the bloodstream. The Greek root Salivary glands, tear glands, and sweat glands are examples of exocrine glands.

watch Balance.


The Endocrine SystemWHAT’S THE POINT?


Besides the nervous system, your body has another system for communicat-ing information. This system, slower to awaken and slower to shut down than the nervous system, is the endocrine system, a set of glands that produce hormones. Hormones are chemical messengers that circulate throughout the body in the blood. Hormones and neurotransmitters are similar in function: Both carry messages, and both communicate by locking into receptor sites.

Figure 4.7 illustrates the major endocrine glands. The most important is the pituitary gland, the endocrine system’s “master gland.” The pituitary gland, in conjunction with an adjacent brain area, controls the other endocrine glands. The brain may call on the pituitary to release hormones that stimu-late or inhibit the release of other hormones from other endocrine glands. The pea- sized pituitary is located at the base of the brain, and it connects to a part of the brain called the hypothalamus. At this connection, the tis-sue is part glandular and part neural, which illustrates the close relationship between the nervous and the endocrine systems.

The brain monitors the levels of hormones circulating in the blood and may be influenced by their levels. Hunger, for example, is a response to a complex inter-action of the nervous system and the endocrine system. The hypothalamus and pituitary gland work together to monitor and control the levels of glucose (blood

Hypothalamus(brain region controlling

the pituitary gland)

Thyroid gland(affects metabolism,among other things)

Pituitary gland(secretes many different hormones, some of which affect other glands)

Adrenal glands(inner part helps

trigger the“fight-or-flight”

response) Pancreas(regulates the level of sugar in the blood)

Ovary(secretes femalesex hormones)

Testis(secretes male sex

hormones)

endocrine [EN- duh- krin] system One of the body’s two communication systems; a set of glands that produce hormones, chemical messengers that circu-late in the blood.

hormone A chemical messen-ger produced by the endocrine glands and circulated in the blood.

pituitary gland The endocrine system’s “master gland” that, in conjunction with an adjacent brain area, controls the other endocrine glands.

Figure 4.7

Major Glands of the Endocrine System

Endocrine glands secrete hormones into the blood-stream. The hormones can influence how we feel and behave.


74

4Differentiation TRMSome important endocrine glands and the hormones they secrete are included in the following list.

● Anterior pituitary gland secretes growth hormone. Too little pro-duces dwarfism; too much results in gigantism.

● Posterior pituitary gland secretes vasopressin, which constricts blood vessels and raises blood pressure.

● Thyroid releases thyroxine and triiodothyronine, which increase metabolism and growth.

● Parathyroids release parathyroid hormone, which regulates blood cal-cium and potassium levels.

● Pancreas secretes insulin, which regulates glucose (sugar) levels in the bloodstream.

● Ovaries secrete estrogen, which pro-motes ovulation and female sexual characteristics.

● Testes release androgens, which promote sperm production and male sexual characteristics.

More information on hormones is available in The Brain (2nd ed.), Module 2: “The Effects of Hormones and the Environment on Brain Development.”

Some important endocrine glands and the hormones they secrete are included

duces dwarfism; too much results in

vasopressin, which constricts blood

hormone, which regulates blood cal-

secrete estrogen, which pro-

promote sperm production and male

Module 2: “The Effects of Hormones


sugar that your cells use for fuel) and insulin (a hormone the pancreas gland secretes, which allows the cells to use the available glucose). This, and a host of other factors, determines how hungry you are at any given moment. The impor-tant pituitary also releases hormones related to physical growth and pregnancy.

Other endocrine glands include the thyroid, the adrenals, and the sex glands (or gonads). The thyroid gland, located in the neck, helps regulate energy level. The adrenal glands, which perch atop the kidneys, release epi-nephrine and norepinephrine (also called adrenaline and noradrenaline). These substances enhance strength and endurance in emergency situations. The sex glands— ovaries in females and testes in males— release hormones that influence emotion and physical development. The primary male hormone is testosterone and the primary female hormone is estrogen, but both males and females have each hormone present in their systems.



I’m seated at my desk right now, working on a computer that will process e- mail, connect to the Internet, and play music on iTunes with a click of the mouse. It does this through a cable modem, which is also the source of the TV program-ming I can access with the remote control that sits next to the cell phone I used to talk to my son, 90 miles away, a few minutes ago. Also on the desk is a stack of bills, delivered by the U.S. Postal Service. Later this afternoon I will pay them— electronically— by using the computer to send instructions to my credit union. I depend on these methods of communication to function effectively in the world, just as my body depends on the nervous system and the endocrine system for its communication needs. These systems are our personal information highways.

SuMMARy AND FoRMATIvE ASSESSMENTMODULE 4 Thinking About the Nervous System and the Endocrine System


WHAT’S THE POINT?


● Neurons are made of dendrites, which receive information and pass it along to the cell body (soma). The axon carries this information to the axon terminals, which release neurotransmitters into the synapse, carrying information to the next neuron.


Apply What you Know

1. What is the general function of neurons?

a. Neurons receive, carry, and pass on informa-tion to other neurons.

b. Neurons rebuild our chemical, electrical, and hormonal systems after stress.

c. Neurons control conscious behaviors. d. Neurons produce hormones to carry mes-

sages to endocrine glands.

2. The axons of some neurons are coated with a __________ sheath.

How Neurons CommunicateThe Neural Impulse

WHAT’S THE POINT?


● Within the cell, a small electrical charge (an action potential) travels down the axon.

Apply What you Know

3. True or False: The firing intensity of a neuron determines the intensity of the response.

4. The __________ period is the recharging phase, during which a neuron, after firing, cannot gen-erate another action potential.


WHAT’S THE POINT?


● The neurotransmitters released from axon termi-nals into the synapse can either excite the next neuron to fire or inhibit it from firing.

Apply What you Know

5. A drug that treats symptoms of depression and affects the sleep cycle probably interacts with

a. dopamine. b. acetylcholine. c. serotonin. d. curare.

6. What does it mean to say that a neurotrans-mitter can excite or inhibit neural impulses?


WHAT’S THE POINT?


● The nervous system is divided into two main sys-tems: the central nervous system (CNS) and the peripheral nervous system (PNS).

● The PNS is divided into the somatic (which con-trols skeletal muscles) and autonomic (which con-trols glands and internal organs) nervous systems.

● The autonomic nervous system is divided into the sympathetic division, which speeds the body up, and the parasympathetic division, which slows it down.

Apply What you Know

7. The fight- or- flight response is triggered by the __________ division of the peripheral nervous system.

8. The peripheral nervous system divides into the __________ nervous system and the __________ nervous system.


WHAT’S THE POINT?


● The endocrine system is a set of glands that com-municate chemically using hormones.

● These glands use hormones to influence many functions within the body, including hunger, energy levels, strength, endurance, and physical development.

Apply What you Know

9. The body’s two communications systems are the nervous system and the __________ system.


BiologyTeam teach a lesson with your school’s biology teacher about how hormones influence both physical and emo-tional behavior.


75

4aSSeSS

ReteachHelp students remember the differ-ences among the nervous systems with these mnemonics:

● Central nervous system The brain and spinal cord are located in the center of the body.

● Peripheral nervous system Fingers and toes lie in the outermost areas, or the periphery, of the body.

● Somatic nervous system Volunteer work is done by choice, so the body’s (or soma’s) voluntary actions are controlled by this nervous system.

● Autonomic nervous system Auto-nomic sounds similar to the word automatic, and the body’s automatic actions (breathing, heartbeat, and so forth) are controlled by this nervous system.

cLoSe

Check for UnderstandingHave students contemplate the ways that problems with the neural and hormonal systems can affect behavior. Encourage students to appreciate the delicate balance our bodies maintain with these systems and how easy it is to upset this balance.

Using the Test BankThe Test Bank that accompanies this textbook offers a wide variety of ques-tions in different formats and levels of complexity. Use the software to construct whole tests or to integrate standardized questions into teacher- made tests.


sugar that your cells use for fuel) and insulin (a hormone the pancreas gland secretes, which allows the cells to use the available glucose). This, and a host of other factors, determines how hungry you are at any given moment. The impor-tant pituitary also releases hormones related to physical growth and pregnancy.

Other endocrine glands include the thyroid, the adrenals, and the sex glands (or gonads). The thyroid gland, located in the neck, helps regulate energy level. The adrenal glands, which perch atop the kidneys, release epi-nephrine and norepinephrine (also called adrenaline and noradrenaline). These substances enhance strength and endurance in emergency situations. The sex glands— ovaries in females and testes in males— release hormones that influence emotion and physical development. The primary male hormone is testosterone and the primary female hormone is estrogen, but both males and females have each hormone present in their systems.



I’m seated at my desk right now, working on a computer that will process e- mail, connect to the Internet, and play music on iTunes with a click of the mouse. It does this through a cable modem, which is also the source of the TV program-ming I can access with the remote control that sits next to the cell phone I used to talk to my son, 90 miles away, a few minutes ago. Also on the desk is a stack of bills, delivered by the U.S. Postal Service. Later this afternoon I will pay them— electronically— by using the computer to send instructions to my credit union. I depend on these methods of communication to function effectively in the world, just as my body depends on the nervous system and the endocrine system for its communication needs. These systems are our personal information highways.

SuMMARy AND FoRMATIvE ASSESSMENTMODULE 4 Thinking About the Nervous System and the Endocrine System


WHAT’S THE POINT?


● Neurons are made of dendrites, which receive information and pass it along to the cell body (soma). The axon carries this information to the axon terminals, which release neurotransmitters into the synapse, carrying information to the next neuron.

ReteachHelp students remember the differences among the nervous systems with these mnemonics:

●

●

●

●

Check for UnderstandingHave students contemplate the ways that problems with the neural and hormonal systems can affect behavior. Encourage students to appreciate the delicate balance our bodies maintain with these systems and how easy it is to upset this balance.

Using the Test BankThe textbook offers a wide variety of questions in different formats and levels of complexity. Use the software to construct whole tests or to integrate standardized questions into teacher-made tests.


Apply What you Know

1. What is the general function of neurons?

a. Neurons receive, carry, and pass on informa-tion to other neurons.

b. Neurons rebuild our chemical, electrical, and hormonal systems after stress.

c. Neurons control conscious behaviors. d. Neurons produce hormones to carry mes-

sages to endocrine glands.

2. The axons of some neurons are coated with a __________ sheath.

How Neurons CommunicateThe Neural Impulse

WHAT’S THE POINT?


● Within the cell, a small electrical charge (an action potential) travels down the axon.

Apply What you Know

3. True or False: The firing intensity of a neuron determines the intensity of the response.

4. The __________ period is the recharging phase, during which a neuron, after firing, cannot gen-erate another action potential.


WHAT’S THE POINT?


● The neurotransmitters released from axon termi-nals into the synapse can either excite the next neuron to fire or inhibit it from firing.

Apply What you Know

5. A drug that treats symptoms of depression and affects the sleep cycle probably interacts with

a. dopamine. b. acetylcholine. c. serotonin. d. curare.

6. What does it mean to say that a neurotrans-mitter can excite or inhibit neural impulses?


WHAT’S THE POINT?


● The nervous system is divided into two main sys-tems: the central nervous system (CNS) and the peripheral nervous system (PNS).

● The PNS is divided into the somatic (which con-trols skeletal muscles) and autonomic (which con-trols glands and internal organs) nervous systems.

● The autonomic nervous system is divided into the sympathetic division, which speeds the body up, and the parasympathetic division, which slows it down.

Apply What you Know

7. The fight- or- flight response is triggered by the __________ division of the peripheral nervous system.

8. The peripheral nervous system divides into the __________ nervous system and the __________ nervous system.


WHAT’S THE POINT?


● The endocrine system is a set of glands that com-municate chemically using hormones.

● These glands use hormones to influence many functions within the body, including hunger, energy levels, strength, endurance, and physical development.

Apply What you Know

9. The body’s two communications systems are the nervous system and the __________ system.


76

4answers Neurons: The Building Blocks of the Nervous System: Apply What You Know

1. (a)

2. myelin

answers The Neural Impulse: Apply What You Know

3. False

4. refractory

answers Communication Between Neurons: Apply What You Know

5. (c)

6. Neurotransmitters serve two broad functions. If they have an excitatory effect, the receiving neuron is more likely to gener-ate an action potential, or fire. If they have an inhibitory effect, the receiving neuron is less likely to generate an action potential.

answers The Structure of the Nervous System: Apply What You Know

7. sympathetic

8. somatic, autonomic

answers The Endocrine System: Apply What You Know

9. endocrine

10. (b)

ate an action potential, or fire. If they have an inhibitory effect, the

The Structure of the Nervous

The Endocrine System: Apply


neuron, p. 62

dendrite, p. 63

axon, p. 63

axon terminal, p. 63

action potential, p. 64

resting potential, p. 64

all- or- none principle, p. 65

synapse [SIN- aps], p. 65

neurotransmitter, p. 65

excitatory effect, p. 66

inhibitory effect, p. 66

receptor cells, p. 67

sensory nerves, p. 67

interneurons, p. 67

antagonist, p. 68

agonist, p. 68

central nervous system (CNS), p. 71

peripheral nervous system (PNS), p. 71

somatic nervous system, p. 71

autonomic [aw- tuh- NAHM- ik] nervous system, p. 71

sympathetic division, p. 72

parasympathetic division, p. 72

endocrine [EN- duh- krin] system, p. 73

hormone, p. 73

pituitary gland, p. 73

K e y T e r m s

10. Which of the following glands is the “master gland”?

a. the testes b. the pituitary c. the thyroid d. the adrenal


domain 2: biopsychology

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