chapt 41 hbio nervous system · 2019-12-07 · a sodium-potassium pump is a carrier protein that...
TRANSCRIPT
Chapter 41 • Nervous System 943
Opening ActivityNervous System Function Askstudents to brainstorm about thefunctions of the nervous system.Write their responses on the chalk-board. Make three columns on thechalkboard with the followingheadings: Monitoring internal and external environments,Coordinating bodily activities, and Functioning of intellect andmemory. Ask students to place their responses into the appropriatecategories. Then ask them toexplain why they grouped theirresponses in this way. VerbalLS
GENERAL
• Vocabulary Worksheets
• Concept Mapping
Chapter Resource File
Answers
1. An ion channel is a transportprotein in a cell membranethrough which ions can pass.
2. A sodium-potassium pump is acarrier protein that transportssodium ions out of, and potas-sium ions into, a cell.
3. Endocytosis is the movementof a substance by a vesicle tothe inside of a cell. Exocytosisis the movement of a substanceby a vesicle to the outside of a cell.
4. Receptor proteins bind to specific signal molecules, causing the cell to respond,forming either open or closedion channels.
Answers
Students may agree or disagreewith the statements. They mayreassess their lists after studyingthe chapter.
Quick Review
Reading Activity
Looking AheadQuick ReviewAnswer the following without referring to
earlier sections of your book.
1. Describe the importance of ion channels in cell
transport. (Chapter 4, Section 1)
2. Identify the role of sodium-potassium pumps in
cells. (Chapter 4, Section 2)
3. Distinguish between endocytosis and
exocytosis. (Chapter 4, Section 2)
4. List three functions of receptor proteins.
(Chapter 4, Section 2)
Did you have difficulty? For help, review the
sections indicated.
Section 1
Neurons and Nerve ImpulsesNeurons
Communication Between Neurons
Section 2
Structures of the Nervous SystemCentral Nervous System
Peripheral Nervous System
Section 3
Sensory SystemsPerception of Stimuli
Eyes
Ears
Chemical Senses
Section 4
Drugs and the Nervous SystemPsychoactive Drugs
Drug Addiction and Neuron Function
Alcohol
Nicotine
Drugs of Abuse
www.scilinks.orgNational Science Teachers Association sciLINKS Internet
resources are located throughout this chapter.
Reading ActivityCopy the following statements in your notebook:
1. Addiction is a purely psychological response
to drug use.
2. Reflexes occur before the brain is aware
of danger.
3. Prolonged exposure to loud noise can cause
permanent hearing loss.
Before you read this chapter, write down
whether you agree or disagree with each
statement. After you have finished reading the
chapter, decide whether or not you still agree
with your first response.
Nerve-cell networks like this one transmit thought,
emotions, and sensations by conducting electro-
chemical signals from cell to cell.
NervousSystem
CHAPTER
41
943
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Overview
Before beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section explains thestructure and function of neurons,the events that occur in synaptictransmission, and the steps of anerve impulse.
Ask students to write definitionsfor electrons and ions and to sug-gest a function of ions in nervecells. Ask them to check their defi-nitions by looking them up in theglossary. (Electrons are negativelycharged particles that move aroundthe nucleus of an atom; ions areatoms or molecules that have either apositive charge [resulting from theloss of one or more electrons] or anegative charge [resulting from thegain of one or more electrons]; nervecells have electrical charges that aredifferent from the electrical chargesin the fluid around them.)
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944 Chapter 41 • Nervous System
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Chapter Resource File
Transparencies
TR Bellringer
TR J59 Structure of a Neuron
• Unit 1—Cell Transport and HomeostasisThis engaging tutorial reinforces cellmembrane structure and function.
BIOLOGYBIOLOGY
Section 1 Neurons and Nerve Impulses
NeuronsIf your body used only chemical signals to send messages, your
interaction with the environment would be slow. A quicker means
of communication is needed, especially if your brain has an urgent
message for the muscles in your legs, such as “Contract quickly! A
speeding car is headed this way!” In addition to chemical signals,
your nervous system uses electrical signals to send messages
rapidly throughout your body.
The nervous system contains a complex network of nerve cells, or
(NOO rahns). Neurons, such as those shown in Figure 1,
are specialized cells that transmit information throughout the body.
Neurons enable many important functions, such as movement,
perception, thought, emotion, and learning.
Structure of NeuronsA neuron’s unique structure enables it to conduct electrical signals
called nerve impulses. Neurons communicate by transmitting nerve
impulses to body tissues and organs, including muscles, glands, and
other neurons. Neurons vary greatly in form, but a typical neuron is
similar to the one shown in Figure 2. (DEHN driets),
which extend from the cell body of the neuron, are the “antennae”
of the neuron. Dendrites receive information from other cells. The
neuron’s cell body collects information from dendrites, relays this
information to other parts of the neuron, and maintains the general
functioning of the neuron. An is a long membrane-covered
extension of the cytoplasm that conducts nerve impulses. The ends
of an axon are called axon terminals. When a neuron communicates
with other cells, it does so at its axon terminals.
Nervous tissue consists mostly of neurons and their supporting
cells. Bundles of axons are called . The arrangement of axons
in a nerve is similar to a telephone cable with many different
communication channels, each carried by a separate wire.
Nerves appear as fine, white threads when viewed with
the unaided eye.
Insulated NeuronsMany neurons have a layer of insulation on their axon
called a myelin (MIE uh lihn) sheath, as shown in Figure
2. Myelin is produced by supporting cells that surround
the axon. The presence of myelin causes nerve impulses to
move faster down the axon. The myelin sheath is inter-
rupted at intervals, leaving gaps called nodes of Ranvier
nerves
axon
Dendrites
neurons
Objectives
● Analyze the structure and
function of neurons.
● Describe how the resting
potential is established in
a neuron.
● Sequence the steps of a
nerve impulse.
● List the events that occur in
synaptic transmission of a
nerve impulse.
Key Terms
neuron
dendrite
axon
nerve
membrane potential
resting potential
action potential
synapse
neurotransmitter
Figure 1 Two neurons.
An average adult human
brain contains about
100 billion neurons.
944
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Using the Figure Have students observe preparedslides or photographs of neuronswith simple morphology (such asstellate neurons). Remind studentsto look for cell bodies, axons, anddendrites. Have students draw andlabel what they see and comparetheir drawings with the neuronshown in Figure 2. Visual
ActivityInformation Transfer Ask stu-dents to recall the game “Telephone”in which one person whispers astatement to his or her neighbor,who whispers the statement to hisor her neighbor, and so on untilthe last person in the room hasheard the statement. Discuss thesimilarities and differences betweenthis game and nerve impulses asthey pass through the body.(Similarities: a nerve impulse, like awhispered statement, passes fromone cell [person] to the next in line.Differences: the whispered statementusually is garbled at the end of theline [the end of the game], but nerveimpulses retain their integrity.)
Interpersonal
Paired Summarizing Pair stu-dents with a partner. Pair Englishlanguage learners with proficientEnglish speakers. Have each stu-dent read silently about restingpotential and action potential onthe following page. Then have oneof the students summarize aloudwhat has been read without refer-ring to the text. The partner shouldlisten without interrupting and be prepared to point out any inaccuracies or omissions in thesummary. At this point studentscan refer to the text. Have students switch roles and repeat the activity.
InterpersonalEnglish Language
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Chapter 41 • Nervous System 945
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Planner CD-ROMdid you know?
Phenylketonuria Phenylketonuria, or PKU, isa disease caused by an enzyme deficiency thatleads to a buildup of phenylpyruvic acid in thebody. This results in the destruction of themyelin sheaths on neurons. If undetected, PKUcan lead to severe mental retardation and evendeath. PKU is easy to detect, so all newbornsin the United States are tested for it. If found,a low phenylalanine diet is prescribed. Foodproducts such as diet sodas carry a message tophenylketonurotics warning them that theproduct contains phenylalanine.
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Topic: Neurons
Keyword: HX4129
(RAHN vee ay), where the axon membrane is exposed to the sur-
rounding fluid. Conduction of nerve impulses is faster in myeli-
nated axons because nerve impulses “jump” from node to node as
they move down the axon. Myelin is especially beneficial in neurons
that must transmit information very rapidly, such as those involved
with quick movement.
The speed of impulse conduction is also related to axon diameter.
A large-diameter axon conducts impulses faster than a small-
diameter axon, assuming both axons are either myelinated or
unmyelinated.
Neuron FunctionAll cells have an electrical charge on the inner surface of the cell
membrane that is different from the electrical charge of the fluid
outside the cell. The difference in electrical charge across the cell
membrane, called the , results from the move-
ment of ions into and out of the cell. This movement depends on
the relative concentration of ions inside and outside the cell, the
ability of the ions to diffuse across the cell membrane, and the elec-
trical charge of the ions. The membrane potential is expressed as
voltage, like that of a battery.
Ions diffuse across a neuron’s cell membrane by passing through
proteins that act as ion channels. Each type of channel allows
only specific ions to pass. Certain channels are voltage-gated—that
is, whether they are open or closed depends on the membrane
potential. Even a small change in the membrane potential can
affect the permeability of the cell membrane to certain ions. As
these ions diffuse into or out of the neuron, they in turn affect the
membrane potential.
membrane potential
Figure 2 Myelinated neuron.
A myelin sheath covers the
axons of many neurons. Myelin
increases the speed of
nerve impulses.
Nucleus
Cell body
Axon terminals
Myelin sheath
Axon
Dendrites
Nodes of
Ranvier
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Vocabulary The term restingpotential is misleading becausethere is constant activity in a neuron even when the neuron isnot conducting a nerve impulse.Ions are continuously beingtransported and diffusing acrossthe membrane.
BUILDERSKILL
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946 Chapter 41 • Nervous System
Analyzing ChangesDuring a NerveImpulse
Skills AcquiredAnalyzing, interpreting,inferring, drawingconclusions
Teacher’s NotesEncourage students to studyFigure 3 on page 947 if theyneed help answering thesequestions.
Answers to Analysis1. The action potential lastsabout 1.5 milliseconds.
2. Voltage gated sodium channelsare open at point A.
3. Voltage gated potassium chan-nels are open at point B.
4. an influx of positively chargedsodium ions
5. an outflow of positivelycharged potassium ions
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The cause of multiple sclerosis (MS) isunknown, but many scientists think that itresults from the actions of the immune systemagainst the myelin sheaths of nerves of thecentral nervous system. The myelin sheaths inthe brain and spinal cord become sclerotic, orhard, causing poor impulse conductivity.Sometimes the symptoms of MS disappearaltogether, but they may return after periodsof remission. Current therapies for MSinclude corticosteroids and beta interferon.
REAL WORLDREAL WORLDCONNECTIONCONNECTION
Transparencies
TR J60 Conduction of a Nerve Impulse
TR J61 Synaptic Transmission
Resting PotentialWhen a neuron is not conducting a nerve impulse, the neuron is
said to be at rest. The membrane potential of a neuron at rest is
called the . In a typical neuron, the resting poten-
tial is negative, about –70 millivolts (mV). At the resting potential,
the inside of the cell is negatively charged with respect to the out-
side of the cell. Why is the resting potential negative? Recall that
sodium-potassium pumps actively transport sodium ions, Na+, out
of a cell and potassium ions, K+, into the cell. This results in a
greater concentration of sodium ions outside the cell than inside
the cell, and a greater concentration of potassium ions inside the
cell than outside the cell. In a neuron, voltage-gated sodium chan-
nels are closed at the resting potential. Thus, very few sodium ions
can diffuse into the cell, despite their strong concentration gradi-
ent. Some voltage-gated potassium channels are open at the resting
potential. Potassium ions can therefore diffuse out of the cell down
their concentration gradient, carrying their positive charge with
them. Neurons also contain negatively charged proteins that are
too large to exit the cell.
Action PotentialWhen a neuron is conducting a nerve impulse, changes occur in the
cell membrane of the neuron. A nerve impulse is also called an
action potential. An is a local reversal of polarity—
from a negative charge to a positive charge—inside the neuron. An
action potential moves down an axon like a flame burning down a
fuse. The events of an action potential are summarized in Figure 3.
action potential
resting potential
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Analysis
1. Determine about how
long an action potential
lasts.
2. State whether voltage-
gated sodium channels are
open or closed at point A.
3. State whether voltage-
gated potassium channels
are open or closed at
point B.
4. Critical Thinking Rec-
ognizing Relationships
What causes the membrane
potential to become less
negative at point A?
5. Critical Thinking Rec-
ognizing Relationships
What causes the membrane
potential to become more
negative at point B?
Background
The graph below illustrates changes that occur in the membrane
potential of a neuron during an action potential. Use the graph to
answer the following questions. Refer to Figure 3 as needed.
Analyzing Changes During a Nerve Impulse
Action Potential
Mem
bra
ne p
ote
nti
al
(mill
ivo
lts)
Time (milliseconds)
A B
+40
+20
0
–20
–40
–60
–80
0 1 2
Reading Effectively
The membrane potential
of a cell is expressed in
millivolts (mV). A millivolt is
equal to one-thousandth of
a volt (V). As shown in the
graph in the Data Lab
below, a neuron’s membrane
potential can be positive
or negative. The resting
potential of an average
neuron is about –70 mV.
During an action potential,
the membrane potential of
the neuron reaches
about +40 mV.
946
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Squid Neurons The squid (Loligo sp.) wasone of the first organisms used to measure theresting potential of a neuron. Because of itslarge, long axons that innervate musclesresponsible for expelling water from the bodycavity, the squid makes an ideal specimen forstudies in cellular neurophysiology. Some ofthese axons are as large as 1 mm in diameter,making them easy to work with.
Using the Figure Figure 3 illustrates action potentialconduction along an axon. Theaxon of this neuron has beenenlarged to show that the mem-brane potential becomes positiveduring an action potential. Tell stu-dents that the reversal of polarityduring an action potential is causedby the rapid influx of sodium ionsthrough voltage-gated sodiumchannels. After an action potentialhas passed, voltage-gated potassiumchannels remain open, causingpotassium ions to diffuse out of thecell. Thus, the membrane repolar-izes shortly after the actionpotential passes. Visual
Interactive Reading AssignChapter 41 of the Holt BiologyGuided Audio CD Program to helpstudents achieve greater success inreading the chapter.
Math Skills A single neuron mayhave synapses onto as many as1,000 other neurons. Have stu-dents calculate how many neuronscould be stimulated if each of these1,000 neurons forms synapses withanother 1,000 neurons. (one millionneurons) Students should readilysee how quickly and widely nerveimpulses can travel. In reality,some of these synapses are excita-tory, while others are inhibitory.Each neuron “evaluates” theimpulses it receives, averages theinput, and responds accordingly.For example, if the overall totalinput is excitatory, the receivingneuron initiates an impulse in aneighboring cell. LogicalLS
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Chapter 41 • Nervous System 947
Dr. Emmeline Edwards, an African-Americanscientist who grew up in Haiti, studies therole that neurochemicals play in coping withstress. Information gained from her researchcan be applied toward the development ofdrugs for treating human depression. Dr. Edwards works at the Department ofPsychiatry at the State University of NewYork, Stony Brook.
MEDICINEMEDICINECONNECTIONCONNECTION
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Step At the resting potential, the inside of the neuron is nega-
tively charged with respect to the outside of the neuron.
The neuron is ready to conduct an action potential.
Step An action potential begins when a stimulus, such as a sig-
nal molecule, causes a local change in the membrane
potential to a more positive value. This change causes
voltage-gated sodium channels to open, and sodium ions
rapidly flow into the axon. For a brief moment, the mem-
brane potential approaches about +40 mV as the inside of
the axon becomes positively charged. This sudden local
reversal of polarity begins a chain reaction that causes
voltage-gated sodium channels to open down the entire
length of the axon. As each sodium channel opens, sodium
ions flow into the axon. The action potential conducts
rapidly down the axon toward the axon terminals.
Voltage-gated sodium channels close immediately after the action
potential has passed. Then additional voltage-gated potassium chan-
nels open, allowing potassium ions to flow out of the axon. As a
result, the membrane potential becomes negative again immediately
after the action potential. The resting potential is fully restored as
sodium-potassium pumps reestablish the original concentrations of
sodium ions and potassium ions inside and outside the axon. The
neuron cannot conduct another action potential until that time.
BIOgraphic
Sodium channel
Sodium
channel
Potassium
channel
Axon
(enlarged)
Potassium
channel
– – – – – – + + + + – – –
– – – – – – + + + + – – –
+ + + + + + – – – – + + +
+ + + + + + – – – – + + +
At the resting potential,
sodium channels are closed
and some potassium
channels are open.
An action potential moves rapidly down an axon.
Conduction of a Nerve Impulse
1
During an action
potential, sodium
channels open,
allowing sodium
ions to move into
the axon.
2
Potassium
ion, K+
Sodium
ion, Na+
Figure 3
947
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Using the FigureHave students identify the den-drites and the cell body, whichreceive inputs, in Figure 4. Thenhave students identify the axon ter-minals, which allow the signal topass to the next neuron in a circuit.Tell students that neurotransmitter molecules are released at the axonterminals, and they then travel toadjacent dendrites and cell bodies.An impulse can travel in only onedirection—away from the cell body of the neuron and toward itsaxon terminals.
Visual
Teaching TipSummarizing an ActionPotential Have students summa-rize in writing the events involvedin the conversion of an actionpotential into a chemical signal atthe synapse. (Answers may vary butshould include depolarization, move-ment of the action potential downthe axon, release of neurotransmittersubstance from the axon terminal,diffusion across the synaptic cleft,and binding to the post-synaptic neu-ron’s membrane.) Verbal
Using the Figure Figure 5 illustrates chemical synap-tic transmission. Neurotransmittermolecules released from a pre-synaptic neuron bind to receptorproteins on a postsynaptic cell,opening ion channels in the post-synaptic cell. Emphasize to studentsthat neurotransmitters can be eitherexcitatory or inhibitory dependingon the nature of the neuron theystimulate and the mechanism oftheir action. VisualLS
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948 Chapter 41 • Nervous System
did you know?
Neurotransmitters and Emotional HealthExtremely small amounts of neurotransmittersunderlie all of our moods, from ecstasy todepression. The neurotransmitters norepi-nephrine and dopamine are involved in feelingsof pleasure. If the levels of these neurotrans-mitters are too low in the brain, we might feeldepressed. Endorphins and enkephalins aresubstances that block pain signals. Their production increases during physical stress,
and runners who experience the increase referto the sensation as a “runner’s high.” Anothercompound, substance P, is released in responseto certain painful stimuli, such as ingestion ofcapsaicin, a chemical irritant in hot peppers.Our neurotransmitter levels react to emo-tional and physical stressors, such as ourthoughts and environment. You literally canhave an “attitude” that can affect your health.
English Language Learners
Communication Between NeuronsA junction at which a neuron meets another cell is called a
(SIHN aps), shown in Figure 4. At synapses, neurons usually do not
touch the cells they communicate with. Between an axon terminal
and a receiving cell is a tiny gap called a synaptic cleft. At a synapse,
the transmitting neuron is called a presynaptic neuron, and the
receiving cell is called a postsynaptic cell.
When a nerve impulse arrives at an axon terminal of a pre-
synaptic neuron, the impulse cannot cross the synaptic cleft.
Instead, the impulse triggers the release of signal molecules called
into the synaptic cleft. Neurotransmitter mol-
ecules are produced by neurons and are stored inside vesicles.
There are many different neurotransmitters and several mecha-
nisms of neurotransmitter action. For example, in human muscles
the principal neurotransmitter is a chemical called acetylcholine
(as ee tihl KOH leen). The brain utilizes several neurotransmitters
such as glutamate (GLOO tuh mayt) and dopamine.
Release of NeurotransmitterA nerve impulse causes a presynaptic neuron to
release neurotransmitter molecules into the synaptic
cleft. When an action potential reaches an axon
terminal of the presynaptic neuron, vesicles that con-
tain neurotransmitter molecules fuse with the cell
membrane. This releases neurotransmitter molecules
into the synaptic cleft by exocytosis. Neurotransmitter
molecules diffuse across the synaptic cleft and interact
with the postsynaptic cell. As shown in Figure 5, neu-
rotransmitter molecules bind to receptor proteins on
the postsynaptic cell. In some cells, ion channels open
when a neurotransmitter binds to these receptor pro-
teins. Such channels are called chemical-gated ion
channels; whether these channels are open or closed
depends on the binding of a chemical—in this case a
neurotransmitter molecule.
A neurotransmitter may either excite or inhibit the
activity of the postsynaptic cell it binds to. For exam-
ple, when the neurotransmitter opens chemical-gated
ion channels, ions move across the cell membrane of
the postsynaptic cell. This causes the membrane
potential of the postsynaptic cell to change depending
on the charge of the ions that move into or out of the
cell. If positively charged ions enter a postsynaptic
neuron, an action potential may be produced (excita-
tion). On the other hand, if positively charged ions
flow out of the postsynaptic neuron, or if negatively
charged ions enter the neuron, an action potential
may be suppressed (inhibition).
neurotransmitters
synapse
Dendrite
Postsynaptic
neuron
Synapses
Axon
terminal
Axons
Presynaptic
neuron
Figure 4 Synapse.
A synapse is a junction at
which signals are transmitted
between a neuron and
another cell.
948
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Answers to Section Review
1. A typical neuron has a bulky cell body studdedwith dendrites, which are membrane-coveredprocesses. One axon, which is a long, mem-brane-covered process, extends from the cellbody to adjacent cells.
2. When ions move across the cell membrane, therelative concentration of ions changes insideand outside the cell. This results in a change ofcharge. The difference in electrical chargeacross a membrane is the membrane potential.
3. At the synaptic cleft, the presynaptic neuronreleases a neurotransmitter substance. Theneurotransmitter diffuses across the synaptic
cleft and binds to the postsynaptic cell, whichbegins a depolarization wave in the next cell.
4. The membrane potential determines whethervoltage-gated ion channels are opened orclosed.
5. A. Incorrect. The myelin sheath is the fattyouter layer found on many neurons. B. Correct. The synapse is the junction at which two neurons communicate. C. Incorrect. A nerve is a bundle of axons.D. Incorrect. A neurotransmitter is a signalmolecule that transmits nerve impulses acrossa synapse.
ReteachingHave students use clay or anothermoldable material to build a modelof a neuron and a synapse. Askthem to label the model, showingat what points the message is elec-trical and at what points the message is chemical. Have the students use arrows to show thedirection of the impulse. Visual
Quiz1. Compare action potential and
resting potential. (At restingpotential, sodium channels areclosed; during action potential,sodium channels are open.)
2. What is membrane potential?(the difference in electrical chargeacross the cell membrane)
3. What must happen to the cellmembrane of a neuron for anaction potential to occur? (Itspotential must become lessnegative.)
AlternativeAssessmentHave each student write a questionon one side of a 335 card for atrivia-type review game of thissection. Have them write theanswer to the question on thereverse side of the card. Collectthe cards and divide the class intotwo teams. Ask the questions andaward points to each team forcorrect responses.
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Chapter 41 • Nervous System 949
Neurotransmitter molecules do not remain in the synaptic cleft
indefinitely. Instead, most neurotransmitter molecules are cleared
from the synaptic cleft very shortly after they are released. Many
presynaptic neurons reabsorb neurotransmitter molecules and use
them again. At other synapses, neurotransmitter molecules are bro-
ken down by enzymes or other chemicals. This happens, for example,
at the synapses between neurons and skeletal muscle cells. The reup-
take or breakdown of the neurotransmitter molecules ensures that
their effect on postsynaptic cells is not prolonged.
Axon
Direction of
action potential
Synaptic
vesicles
Ion
channel
Neurotransmitter
molecule
Axon
terminal
Synaptic
cleft
Postsynaptic
cell
Presynaptic
neuron
Receptor
proteins
When neurotransmitter
molecules are released
from a presynaptic
neuron, they either
excite or inhibit a
postsynaptic cell.
Neurotransmitter molecules are released from a presynaptic neuron,
diffuse across the synaptic cleft, and interact with a postsynaptic cell.
Figure 5 Synaptic transmission
Section 1 Review
Describe the structure of a typical neuron.
Describe how the movement of ions across the cell membrane determines the membranepotential.
Summarize the events involved in the synaptictransmission of a nerve impulse.
Critical Thinking Inferring Relationships
How does the membrane potential affect thepermeability of a neuron’s cell membrane?
The junction at which aneuron communicates with another neuron or a muscle cell is called a
A myelin sheath. C nerve.
B synapse. D neurotransmitter.
Standardized Test PrepStandardized Test Prep
949
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CareerCareerMedical Imaging Technician Have studentsprepare a report on the job of a medical imagingtechnician. They should include descriptions ofthe different medical procedures these workersperform, such as computerized axial tomogra-phy (CAT), magnetic resonance imaging (MRI),and positron emission tomography (PET). Theyshould also include a description of training nec-essary and starting salary. Have them write abrief report on what they found. Ask for volun-teers to read their reports to the class.
Overview
Before beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section explores thecentral nervous system, the periph-eral nervous system, the autonomicnervous system, and the somaticnervous system. The major partsand functions of the brain are dis-cussed, as well as the spinal cordand spinal reflex.
Ask students to make a list of reflexbehaviors. (Examples include blink-ing, swallowing, kneejerk, recoilingfrom a hot surface.) Have studentsindicate which, if any, of thesebehaviors require consciousthought.
Demonstration
Have a volunteer stand at the frontof the room. While talking to theclass, suddenly snap your fingersdirectly in front of the volunteer’sface. He or she will blink reflex-ively when you snap your fingers.Ask students if a person can over-come a reflex such as blinkingwhen something comes towardtheir eyes unexpectedly. (Answerswill vary.) Try snapping again a fewmore times. Ask the student volun-teer if he or she was able to controlthe blinking reflex. (Yes, if the stu-dent is expecting the noise, he or shewill probably be able to consciouslycontrol their blinking response overtime.) KinestheticLS
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950 Chapter 41 • Nervous System
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TR Bellringer
TR J63 Structure of the Human Brain
Central Nervous SystemNeurons are the most important cells of the nervous system. The func-
tions of the nervous system depend on the complex interaction
between billions of neurons. Networks of neurons constantly gather,
integrate, interpret, and respond to information about the body’s inter-
nal state and environmental conditions. How are neurons organized in
the nervous system? As shown in Figure 6, there are two main divi-
sions of the nervous system—the central nervous system, shown in
orange, and the peripheral nervous system, shown in purple. The
(CNS) consists of the brain and the spinal
cord. The CNS is the control center of the body. The CNS interprets
and responds to information from
the environment and from with-
in the body. The
(PNS) contains sensory neu-
rons and motor neurons.
send information from
sense organs, such as the skin, to
the CNS. send com-
mands from the CNS to muscles and
other organs.
BrainThe is the body’s main pro-
cessing center. Encased entirely
within the skull, the brain contains
about 100 billion neurons. An aver-
age adult brain weighs about 1.5 kg
(3 lb). Thoughts, feelings, emo-
tions, behavior, perception, and
memories are controlled by your
brain. Your brain also enables you
to learn and process information,
such as the text in this book. Scien-
tists have determined the location
of various functions in the brain.
The brain consists of three major
parts, shown in Figure 7—the cer-
ebrum, the cerebellum, and the
brain stem.
brain
Motor neurons
neurons
Sensory
system
peripheral nervous
central nervous system
Section 2 Structures of theNervous System
Objectives
● Distinguish between the
central nervous system
and the peripheral nervous
system.
● Identify the major parts
of the brain and their
functions.
● Describe the structure
of the spinal cord.
● Sequence the events
of a spinal reflex.
● Compare the somatic
nervous system with
the autonomic nervous
system.
Key Terms
central nervous
system
peripheral nervous
system
sensory neuron
motor neuron
brain
cerebrum
cerebellum
brain stem
thalamus
hypothalamus
spinal cord
reflex
interneuron
Nervous System
Brain
Spinal
cord
Figure 6 Nervous system.
The central nervous system
(orange) consists of the brain
and the spinal cord. The
peripheral nervous system
(purple) branches throughout
the body.
950
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Teaching TipNervous System As studentsread about the nervous system,have them construct a GraphicOrganizer similar to the one at thebottom of this page that describesthe main structures of the nervoussystem. Have them use the follow-ing terms: autonomic nervoussystem, brain, central nervous sys-tem, nervous system, peripheralnervous system, spinal cord, andsomatic nervous system.
Teaching TipMeningitis Remind students thatthe brain is encased in the skull. Inaddition, tough protective mem-branes known as meninges coverthe brain. A disease known asmeningitis results when bacteria orviruses cause inflammation of themeninges. Meningitis can be fatal ifnot treated quickly.
Using the Figure Have students review the parts ofthe brain as labeled in Figure 7.Point out that the brain is dividedinto a right and a left half, whichare connected by the corpus callo-sum. Ask students if they thinkthey are right-brained or left-brained. Although in most people,both parts of the brain worktogether, some people rely moreon one side or the other. Peoplewho rely more on their rightbrain tend to be more imagina-tive and intuitive, whereas people who rely more on their left brain tend to be more logicaland analytical.
VisualLS
TeachTeach
Chapter 41 • Nervous System 951
Answer
Answers will vary. Proponents ofhelmet laws may cite the largecost, usually borne by the public,of caring for head-injury victims.
Real Life
Ed:Moved ELL logo per edits,but now not to spec. OK?
Ed:Leveling on Real Life OK?
Cerebrum The (seh REE bruhm) is the largest part of the
brain. The capacity for learning, memory, perception, and intellec-
tual function resides in the cerebrum. The cerebrum has a folded
outer layer with many bumps and grooves. A long, deep groove
down the center divides the cerebrum into right and left halves, or
hemispheres. The cerebral hemispheres communicate through a
connecting band of axons called the corpus callosum (KOR puhs
kuh LOH suhm). In general, the left cerebral hemisphere receives
sensations from and controls movements of the right side of the
body. The right cerebral hemisphere receives sensations from and
controls movements of the left side of the body.
Most sensory and motor processing occurs in the cerebral cortex
(KOHR teks), the folded, thin (2–4 mm) outer layer of the cerebrum.
The cerebral cortex contains about 10 percent of the brain’s neu-
rons. The folded outer surface of the cerebrum is the cerebral cor-
tex, which has a large surface area. The cerebral cortex is primarily
involved with the functioning of sensory systems.
Cerebellum The (ser uh BEL uhm), which is located at
the posterior base of the brain, regulates balance, posture, and
movement. The cerebellum smooths and coordinates ongoing
movements, such as walking, by timing the contraction of skeletal
muscles. The cerebellum integrates and responds to information
about body position from the cerebrum and the spinal cord to con-
trol balance and posture.
Brain Stem At the base of the brain is the stalklike . The
brain stem is a collection of structures leading down to the spinal
cord and connecting the cerebral hemispheres with the cerebellum.
The lower brain stem consists of the midbrain, the pons, and the
brain stem
cerebellum
cerebrum Real Life
Each year, nearly 250
bicyclists die because
of brain injuries.
Wearing a bicycle helmet
reduces the risk of head
trauma by more than
70 percent.
Evaluating Viewpoints
Should there be helmet
laws for bicyclists just as
there are seatbelt laws for
automobile
drivers?
CerebrumThalamus
Corpus callosumHypothalamus
Cerebellum
Spinal cord
Midbrain
Pons
Medulla
oblongata
Upper brain
stem
Lower brain
stem
Figure 7 Brain. The
cerebrum is divided into two
hemispheres. This view shows
the right hemisphere.
951
English Language Learners
Use this graphic organizer with
Teaching Tip on this page.
Graphic Organizer
Brain
Spinal cord
Somatic
nervous system
Autonomic
nervous system
Nervous system
Central
nervous system
Peripheral
nervous system
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Discussion Ask students if theythink there are structural or physicaldifferences in the brains of peoplewho are considered to be geniuses.Ask students if they think AlbertEinstein’s brain, for example, mightshow differences that indicate hisgenius. Dr. Einstein was a brilliantscientist who won a Nobel Prize inphysics in 1921. He permitted hisbrain to be preserved after his deathfor study. Scientists at McMasterUniversity, Ontario, Canada com-pared the size and shape of his brainto those of 91 men and women ofaverage intelligence and found thatEinstein’s brain was 15% wider inone region. Other studies have beendone to determine if his brain wasstructurally different from the brainsof average human brains. To date,no conclusive findings have beenmade to relate any differences inbrain structure to intelligence.
Demonstration Have students work in pairs todemonstrate reaction time. Haveone student of each pair hold aruler vertically. Have the other student position his or her fingers1 inch below the ruler, in a pinch-ing mode. (This works best if theforearm rests on a table.) Have thefirst student drop the ruler withoutwarning. The other student shouldtry to catch it between the thumband index finger. The shorter thesegment allowed to fall through thefingers, the quicker the reactiontime. KinestheticLS
GENERAL
SKILL
BUILDER
READINGREADING
Teach, continuedTeach, continued
952 Chapter 41 • Nervous System
Medical scientists think that some psychoso-matic illnesses may be mediated by thehypothalamus through its connections to theautonomic nervous system and the endocrinesystem. Many stress-related illnesses, such asulcers, asthma, and high blood pressure, areclearly connected to hypothalamic functions.
REAL WORLDREAL WORLDCONNECTIONCONNECTION
MISCONCEPTION
ALERT
Brain Size Students may believe that mod-ern Homo sapiens have the largest brains ofany hominid in history. Remind students thatNeanderthals had larger brains than those ofsome modern humans. The brains of modernhumans are much more convoluted thanthose of Neanderthals. This suggests thatintelligence may be related more to theextent of the convolutions (which is relatedto the area of the cerebral cortex) than tooverall brain size.
medulla oblongata (mi DUHL uh ahb lahn GAHT uh). These struc-
tures relay information throughout the CNS and play an important
role in homeostasis by regulating vital functions, such as heart rate,
breathing rate, body temperature, and sleep.
The upper brain stem contains important relay centers that
direct information to and from different parts of the brain. The
(THAL uh muhs) is a critical site for sensory processing.
Sensory information from all parts of the body converges on the
thalamus, which relays the information to appropriate areas of the
cerebral cortex. Below the thalamus, at the base of the brain, is the
hypothalamus. The , along with the medulla oblon-
gata, helps regulate many vital homeostatic functions, such as
breathing and heart rate. The hypothalamus is responsible for feel-
ings of hunger and thirst. It also regulates many functions of the
endocrine system by controlling the secretion of many hormones.
The thalamus and hypothalamus are linked to some areas of the
cerebral cortex by an extensive network of neurons called the limbic
system. The limbic system includes structures of both the brain stem
and the cerebrum. The limbic system has an important role in mem-
ory, learning, and various emotions, such as pleasure and anger.
Spinal CordThe , shown in Figure 8, is a dense cable of nervous tis-
sue that runs through the vertebral column. The spinal cord extends
from the medulla oblongata through the vertebrae to a level just
below the ribs. The spinal cord links the brain to the PNS. The brain
receives information that travels upward through the spinal cord.
Through the spinal cord, the brain also sends commands that con-
trol the rest of the body. In addition to relaying messages, the spinal
cord functions in reflexes. A is a sudden, involuntary con-
traction of muscles in response to a stimulus.
reflex
spinal cord
hypothalamus
thalamus
Interpreting Graphics
As you look at Figure 8,
think of the spinal cord as
a busy two-way highway
with sensory traffic going
north and motor traffic
going south.
Sensory
input
Back of body
Front of body
Cross section of spinal cord
Motor
outputGray matterNerve
fibers
Ventral
root
Dorsal
root
ganglion
White matter
Spinal
nerve
Spinal
nerve
Spinal nerves have a dorsal root and a ventral root that diverge as they enter the spinal cord.
Figure 8 Spinal cord
952
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Teaching Tip Encourage interested students touse the Internet Connect box onthis page to find out more aboutcurrent research into the cure forspinal cord injury. Have studentsgive a brief oral report to the classpresenting what they find.
VerbalLS
Chapter 41 • Nervous System 953
Spinal Cord Injury
Teaching StrategiesBring in pictures of ChristopherReeve and other people whohave paralysis as a result ofspinal cord injuries. If the infor-mation is available, talk abouthow they were injured. Wereany of the injuries preventable?
Discussion
• Why does paralysis occur?(Nerve impulses cannot cross the site of injury in thespinal cord.)
• Is it possible for a person tohave arms but not legs para-lyzed as the result of a spinalcord injury? Explain youranswer. (No, because every-thing below the spinal cordinjury is affected. If the injuryis above the spinal cord areathat controls the arms, all fourlimbs are affected.)
• Would you volunteer to be atest case for the methodsdescribed if you had a spinalcord injury? Why or whynot? (Answers will vary.)
MISCONCEPTION
ALERT
Brain Tumors Because most neurons donot undergo mitosis in adult humans,students may think that a brain cannotdevelop a tumor. Brain tumors, however,are not formed from neurons. They arisefrom the supportive glial cells in the nerv-ous system, which do undergo mitosis.
Transparencies
TR J64 Structure of the Human Spinal Cord
TR J66 Knee-Jerk Reaction
TR J67 Physiological Effects of theAutonomic Nervous System
The spinal cord is linked to the PNS through 31 pairs of spinal
nerves. The spinal nerves, which branch from the spinal cord, carry
information to and from the CNS. Spinal nerves in the upper part
of the spinal cord branch into the arms and upper body, and spinal
nerves in the lower part of the spinal cord branch into the legs and
lower body. Each spinal nerve has a dorsal root and a ventral root.
Dorsal roots contain sensory neurons, which carry information
from areas of sensory input to the CNS. Ventral roots contain motor
neurons, which carry motor responses from the CNS to muscles,
glands, and other organs. As shown in Figure 8, dorsal and ventral
roots come together to form the spinal nerves near the spinal cord.
The spinal cord contains a core of gray matter covered by a
sheath of white matter, as shown in Figure 8. Gray matter contains
the cell bodies of neurons, whereas white matter contains the axons
of neurons. Included in the gray matter are , which
link neurons to each other.
interneurons
Spinal Cord Injury
Unlike most other parts of the
body, the spinal cord does
not heal after an injury. Damaged
neurons stop conducting nerve
impulses at the site of injury, per-
manently paralyzing the legs or,
in some cases, all four limbs.
Every year, spinal cord
injuries—whether incurred in
athletics or automobile acci-
dents—leave nearly 15,000
Americans partially or totally par-
alyzed. In 1995, actor Christo-
pher Reeve, shown in the photo
at right, injured his spinal cord
after falling headfirst from a
horse. The fall broke vertebrae in
Reeve’s neck, paralyzing him
from the neck down.
A treatment currently available
for people with spinal cord
injuries is an anti-inflammatory
drug called methylprednisolone.
If given within 8 hours after the
spinal cord is injured, the drug
can improve chances of recov-
ery. Even with this drug, how-
ever, recovery is usually far from
complete.
Stopping Cell Death
Cells continue to die near the
site of a spinal cord injury for
several weeks after injury
occurs. Myelin-producing cells
die, leaving neurons in the spinal
cord unable to function. Some
scientists think that stopping the
death of these cells could help
avoid paralysis. In experiments
on rats, researchers have found
that a cell-death inhibitor
improves the rats’ ability to use
their hind legs after a spinal cord
injury. Researchers are investi-
gating other cell-death inhibitors
that could be used on humans.
Bridging the Gap
After the spinal cord is injured,
damaged axons begin to regrow.
However, their growth is inhib-
ited by substances in the spinal
cord. Peripheral nerves lack
these substances, so the axons
in these nerves can regrow quite
well. To stimulate the growth of
axons in the injured spinal cord,
researchers have grafted pieces
of peripheral nerves into the
spinal cord. The nerve grafts
provide tunnels for regrowing
axons. Rats with such nerve
grafts begin to show signs of
recovery within 3 weeks. Within
a year, they can support their
own weight. Similar grafts have
not yet been tried on humans.
www.scilinks.org
Topic: Spinal Cord
Keyword: HX4168
953
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Paired Summarizing Have stu-dents choose a partner. Have bothpartners read silently about theperipheral nervous system on thispage and the facing page. Thenhave one student summarize aloudwhat has been read without refer-ring to the textbook. The partnershould listen without interruptingand be prepared to point out anyinaccuracies or omissions in thesummary. Students may refer tothe text to verify the facts. Thenhave students switch roles.
InterpersonalLS
SKILL
BUILDER
READINGREADING
Teach, continuedTeach, continued
Referred Pain Referred pain is pain thatoriginates in a location different from where itis felt. Referred pain is important in clinicaldiagnoses. For example, inadequate oxygena-tion of the heart muscle often results in painbeing referred to the chest wall and shoulder.Inflammation of the appendix, in the lowerright quadrant of the abdomen, is sometimesfelt as pain in the navel area.
954 Chapter 41 • Nervous System
Relate membrane, resting, and action potentials topotential difference. Potential difference is the changein the electrical potential energy of a charged particledivided by its mass and is measured in volts (V). Inaddition, remind students that electrical potential ener-gy is increased if a force pushes electrical charges inthe direction opposite the electric force. Check theirunderstanding by asking what biological mechanismpushes electrical charges opposite the electric force.(the sodium-potassium pumps.)
Integrating Physics and Chemistry
StrategiesStrategiesINCLUSIONINCLUSION
Have students work with a partner to make observations ofhow the body keeps a sense ofbalance. With the partner stand-ing perfectly still, feet together,and his or her eyes closed for oneminute, have the student observefrom the side to see how muchthe subject wavers back andforth. Next, observe the subjectfrom behind to see if there is anywavering from side to side. Writethese observations down. Repeatthe test after switching roles.Students may report to the classtheir findings.
• Attention Deficit Disorder• Learning Disability
Peripheral Nervous SystemThe peripheral nervous system connects the brain and the spinal cord
to the rest of the body. In addition to the 31 pairs of spinal nerves, 12
pairs of cranial nerves connect the brain with areas in the head and
neck. The PNS contains two principal divisions—the sensory division
and the motor division. The sensory division directs sensory informa-
tion to the central nervous system. The motor division carries out
responses to sensory information. The motor division of the PNS con-
sists of two independent systems—the somatic nervous system and
the autonomic nervous system.
Somatic Nervous SystemMost motor neurons that stimulate skeletal muscles are under our
conscious control. These neurons are part of the somatic nervous
system. Some activity in the somatic nervous system, such as spinal
reflexes, is involuntary. A spinal reflex is a self-protective motor
response. Spinal reflexes are extremely rapid because they usually
involve the spinal cord but do not involve the brain.
The knee-jerk reflex, shown in Figure 9, is an example of a spinal
reflex. When the ligament below your kneecap is tapped, your lower
leg suddenly kicks forward. Tapping the ligament stimulates a sensory
neuron, shown in red. The sensory neuron sends a nerve impulse to
the spinal cord and excites a motor neuron, shown in green, which
causes the quadriceps to contract. This causes the leg to extend
rapidly. The sensory neuron also stimulates an interneuron, shown in
blue. The interneuron inhibits a motor neuron that would normally
cause the hamstrings to contract, allowing the hamstrings to relax.
Quadriceps
Patellar
ligament
Hamstrings
Sensory
neuron
Dorsal
root
Spinal
cord
Ventral root
Motor
neuron to
quadriceps
Motor
neuron to
hamstrings
Interneuron
Patella
(kneecap)
When the ligament below the patella is tapped, the quadriceps contracts,
the hamstrings relax, and the leg rapidly extends.
Figure 9 Knee-jerk reflex
Interpreting Graphics
As you look at Figure 9,
notice that in a spinal reflex,
motor neurons stimulate
muscles in the same region
in which the stimulus that
caused the reflex originated.
954
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Answers to Section Review
1. The two main divisions of the nervous systemare the central nervous system and the periph-eral nervous system. The central nervous system,consisting of the brain and spinal cord, is thecontrol center of the body. The peripheralnervous system connects the brain and spinalcord to the rest of the body.
2. The cerebellum regulates balance and the timing of movement, while the brain stem regulates vital functions such as breathing,heart rate, body temperature, and sleep.
3. Dorsal roots contain sensory neurons; ventralroots contain motor neurons.
4. The parasympathetic division is more active.
5. A spinal reflex travels only as far as the spinalcord, whereas a voluntary movement involvesthe brain and therefore takes longer than aspinal reflex.
6. A. Incorrect. The patella does not change. B. Incorrect. The hamstrings will relax if thequadriceps contract. C. Incorrect. The quadri-ceps will elongate if the hamstrings contract. D. Correct. For the knee to jerk, the quadricepsmust contract.
ReteachingOn the chalkboard or overheadprojector, list the major conceptspresented in this section. Have theclass review the text to identifyexamples that can be used to illus-trate each of these concepts.
Quiz1. What might be the result from
damage to the cerebellum? (lossof balance)
2.What controls the “fight orflight” response? (sympatheticdivision of the autonomic nervoussystem)
3. What do the hypothalamus andthe medulla oblongata regulate?(vital homeostatic functions)
AlternativeAssessmentHave pairs of students take turnslightly tapping each other’s legslightly below the knee. If possible,have them use a rubber-headedhammer borrowed from the schoolnurse. Ask students to each write abrief summary of their observationsand the cause of the effect produced.Tell them that their summary mustinclude the following terms: reflex,axon, synapse, motor neuron, sensory neuron, spinal cord.
GENERAL
GENERAL
CloseClose
Chapter 41 • Nervous System 955
Autonomic Nervous SystemPeripheral motor neurons that regulate smooth muscles do not
require our conscious control. These neurons are part of the auto-
nomic nervous system, which regulates heart rate and blood flow
by controlling contractions of cardiac muscle in the heart and
smooth muscle lining the walls of blood vessels. It also controls
muscles in the digestive, urinary, respiratory, and reproductive sys-
tems, as well as the secretions of many glands.
Two divisions of the autonomic nervous system—the parasympa-
thetic division and the sympathetic division—maintain stability in the
body by counterbalancing each other’s effects. The parasympathetic
division is most active under normal conditions. It keeps your body
functioning even when you are not active. For example, you continue
to breathe when you fall asleep.
The sympathetic division dominates in times of physical or emo-
tional stress. It controls the “fight-or-flight” response that you
experience during a stressful situation, such as “nervousness” when
taking a pop quiz. The sympathetic division increases blood pres-
sure, heart rate, and breathing rate. It also directs blood flow toward
your heart and skeletal muscles. Effects of the autonomic nervous
system are summarized in Table 1.
www.scilinks.org
Topic: AutonomicNervous System
Keyword: HX4017
Table 1 Physiological Effects of the Autonomic Nervous System
Organ Effect of sympathetic division Effect of parasympathetic division
Eyes Pupils dilate Pupils constrict
Heart Heart rate increases Heart rate decreases
Lungs Bronchioles dilate Bronchioles constrict
Intestines Gastric secretions decrease Gastric secretions increase
Blood vessels Blood vessels dilate Little or none
Name the two main divisions of the nervoussystem, and state their general functions.
Compare the functions of the cerebellum andthe brain stem.
Distinguish between dorsal roots and ventralroots of the spinal cord.
Name the division of the autonomic nervous system that is more active under normal conditions.
Critical Thinking Comparing Functions
Why is a spinal reflex more rapid than a voluntarymovement?
A sudden stretch of thequadriceps muscle triggers the knee-jerk reflex,which maintains homeostasis by causing the
A patella to elongate.
B hamstrings to contract.
C quadriceps to elongate.
D quadriceps to contract.
Standardized Test PrepStandardized Test Prep
Section 2 Review
955
Copyright © by Holt, Rinehart and Winston. All rights reserved.
OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section explores thesenses. The structures and mecha-nisms of touch, vision, hearing,taste, and smell are described.
Ask students each to select anobject in the room. Ask them topoint to a specific place on theobject with their index finger.Direct them to focus on that place,first with both eyes open, thenwith just the left eye closed, andfinally with just the right eyeclosed. Have students write downwhat happens to the image andoffer an explanation. (Each eyeregisters an image that is slightlydifferent from the other. When botheyes are used, the brain combines theimages to create a new image.)
ActivityPhosphenes Have students closetheir eyes and press lightly on theireyelids. Ask what they see. (patternsof colors) These patterns are calledphosphenes. The nerves in the eyessend messages to the brain, whichinterprets these messages as colors.Then ask what this phenomenontells them about the sense of sight.(The eyes respond to visual stimuli.The brain is interpreting pressurestimuli as visual stimuli.) VisualLS
GENERAL
MotivateMotivate
Bellringer
FocusFocus
Section 3
956 Chapter 41 • Nervous System
• Directed Reading
• Active Reading
• Data Sheet for Quick Lab GENERAL
GENERAL
Chapter Resource File
Transparencies
TR Bellringer
TR J68 Types of Sensory Receptors
TR J62 Cortex
Remind students that electric circuits—likenerve pathways—usually have a switch, whichopens and closes the path in order to stop orpermit the flow of charges through the electriccurrent. Whereas the switch is often amechanical device in an electric circuit, it isthe synapse for nerve pathways.
Integrating Physics and Chemistry
Section 3 Sensory Systems
Perception of StimuliThe perception of everything you respond to in the environment,
such as the horn of a passing car or cold rain on your face, is made
possible by sensory systems. Sensory systems are essential to sur-
vival, and they enable us to experience both pleasurable and painful
stimuli. Sensory systems help maintain homeostasis by constantly
adjusting body conditions to respond to changes in the environ-
ment. This requires the integration of the peripheral nervous system
and the central nervous system. The sensory division of the PNS col-
lects information about sensory stimuli in and around the body. The
sensory information is sent to the brain, which processes the infor-
mation and, if necessary, generates a motor response to the stimuli.
How does the nervous system detect sensory stimuli? Specialized
neurons called detect sensory stimuli and then
convert the stimuli to electrical signals, in the form of nerve impulses,
that can be interpreted by the brain. Although sensory receptors are
located throughout the body, they are most concentrated in the sense
organs—the eyes, ears, nose, mouth, and skin. Table 2 lists several
types of sensory receptors and some of their locations.
Sensory ReceptorsMechanoreceptors throughout the body respond to physical stimuli—
such as pressure and tension—that cause distortion or bending of
tissue. These stimuli alter the electrical activity of mechanoreceptors.
Many mechanoreceptors are found in the skin, and they are concen-
trated in very sensitive areas, including the face, hands, fingertips,
and neck. Pain receptors, which respond to potentially harmful
stimuli—such as intense heat or cold and tissue damage—are respon-
sible for painful sensations. Pain is a very important sensation
sensory receptors
Objectives
● List five types of sensory
receptors and the stimuli to
which they respond.
● Identify sites of sensory
processing in the brain.
● Analyze the structure of
the eye and its role in the
visual system.
● Describe how the ear
detects sound and helps
maintain balance.
● Compare the senses of
taste and smell.
Key Terms
sensory receptor
retina
rod
cone
optic nerve
cochlea
semicircular canal
www.scilinks.org
Topic: Sensory Receptors
Keyword: HX4162
Table 2 Types of Sensory Receptors
Receptor type Stimuli Locations
Thermoreceptors Temperature change Skin, hypothalamus
Pain receptors Tissue damageAll tissues and organs
except the brain
MechanoreceptorsMovement, pressure,
Skin, ears, musclestension
Photoreceptors Light Eyes
Chemoreceptors Chemical Tongue, nose
956
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Phineas Gage On September 13, 1848, anaccidental explosion on a Vermont railroadcaused an extremely unusual injury. A railwayforeman named Phineas Gage was settingexplosive charges with a tamping iron, aheavy iron rod. One of the charges exploded,sending the tamping iron through the left sideof his skull. It entered under his left cheek-bone, exited through the top of his head, andlanded 25 yards away. Most of the left frontallobe of his brain was destroyed, but it is said
that Gage never even lost consciousness. After seven months of recuperation, Gage waswell enough to return to work. His physicaland intellectual functions were unchanged,but his personality was completely different.Once polite and patient, he became profane,impatient, and rude, and was unable toresume his work as a foreman. His horrificinjury, however, greatly influenced physiciansand scientists who were attempting to deter-mine how function is localized in the brain.
Teaching TipTouch Receptors Tell studentsthat although touch receptors arespread throughout the skin, someareas have a larger concentrationof touch receptors than others. For example, lips and hands havelarge numbers of touch receptorssituated close together. It is easy todistinguish two points at very closedistances on skin covering the lipsand hands. However, on the backthere are areas where touch recep-tors are several millimeters apart.Tell students that they may not beable to distinguish two differentpoints that are touched on theirbacks because of this.
Activity Visual Feedback and TouchHave students work in pairs. Onestudent should hold his or herarms out and crossed so that thepalms meet, and the fingers areinterlocked. Have students bendtheir elbows and move the handsdown and in toward the body.Keep the elbows bent, and bringthe hands close to the body, twist-ing the hands upward. Have thepartner point to a finger withouttouching it. The student should tryto move that finger quickly. Askstudents to share what happens.(The student will have difficultyidentifying and moving the fingerindicated by his or her partner. Thisis because the eyes confirm bodypositions that are monitored by positional receptors, called proprio-ceptors. If the hands are in anunusual position, proprioceptors and the eyes send conflicting mes-sages to the brain.) Ask students ifit is easier to identify the finger ifthe partner first touches that finger.(Yes, because touch receptors giveadditional information to the brain.)
KinestheticLS
GENERAL
TeachTeach
Chapter 41 • Nervous System 957
• Reading Organizers
• Reading Strategies
Planner CD-ROM
because it informs you that something is wrong in your body. Many
self-protective responses, such as reflexes, are initiated by pain
receptors. Thermoreceptors, located in the skin and hypothalamus,
detect changes in temperature. Thermoreceptors play an important
role in homeostasis, helping to keep the body temperature within
its normal range.
Sensory receptors are located throughout the body, and sensory
input from these receptors enters the central nervous system in an
organized fashion. Sensory stimuli that originate in the lower body
enter the lower part of the spinal cord. Sensory stimuli that origi-
nate in the upper body enter the upper part of the spinal cord and
the brain.
Processing of Sensory InformationRecall that the cerebral cortex contains a large percentage of the
brain’s neurons. Many of the neurons in the cerebral cortex are
responsible for processing incoming sensory information from the
sense organs. The thalamus relays information from the sense
organs to certain regions of the cerebral cortex. As shown in
Figure 10, deep grooves divide the cerebral hemispheres into four
general areas, or lobes: the occipital (ahk SIP ih tuhl) lobe, the pari-
etal (puh RIE uh tuhl) lobe, the temporal lobe, and the frontal lobe.
Sensory neurons from the different sense organs come together at
certain regions in the cerebral cortex. For example, most visual proc-
essing takes place in the occipital lobe, located at the back of the
head. Similarly, processing of sound is carried out within the
temporal lobe.
Frontallobe
Frontal lobe Parietallobe
Parietal lobe
Vision
Occipital lobe
Cerebellum
Side view of brain(left hemisphere)
Righthemisphere
Lefthemisphere
Top view of brain
Smell
Speech
Taste
Hearing
Occipitallobe
Motor function
Intellectual function
Sensory function
Temporallobe
Specific areas of the cerebral cortex control different functions of the body.
Figure 10 Processing sites and lobes of the cerebral cortex
957
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Demonstration
You will need a cardboard tubefrom a roll of paper towels for thisdemonstration. Tell a student vol-unteer to keep both eyes open, andto place the tube over his or herleft eye. Have the student hold hisor her right hand next to the endof the tube, and move it slowlyalong the tube toward his or herface. Ask the student what he orshe observes. (It should appear asthough the tube passes through thepalm of the hand. The brain auto-matically combines the images seenwith both eyes into one picture.)
VisualLS
GENERAL
Teach, continuedTeach, continued
Tell students that if they stare at a picture longenough and then look at a white wall, theywill see the same image shapes, but with dif-ferent colors. Give students pieces of blackconstruction paper with large blue spots in themiddle. After they have stared at the blackpaper for a minute, have them look at a whitewall. Ask students what color spot they see onthe white wall. (Students should see a red spot.)
958 Chapter 41 • Nervous System
DemonstratingYour Blind Spot
Skills AcquiredSummarizing, drawingconclusions, applyinginformation
Teacher’s NotesMake sure students are closingtheir right eyes and are lookingat the O. It should disappearabout 1 ft from the end of thenose. Try the lab with the Xand the left eye as well.
Answers to Analysis1. rods and cones
2. There are no photoreceptors(rods and cones) at that spot.
3. The X disappears when it is inthe part of the visual fieldmediated by the part of theretina where there are no photoreceptors.
did you know?
Glaucoma Glaucoma is an eye disease inwhich increased pressure inside the eye causesdamage to the retina and the optic nerve. Thecause of the increased pressure is a buildup ofthe aqueous humor, the fluid interior of theeye. Glaucoma is the second most commoncause of blindness.
Transparencies
TR J72 Structure of the Eye
TR J69 Anatomy of the Ear
Eyes
Humans have very good eyesight. Our eyes enable us to see in color
and to distinguish fine details and movement. The structure of the eye
is shown in Figure 11. Light enters the eye through the pupil. Light
then passes through the lens, a thick, transparent disk that focuses
light on the retina. The is a lining on the back inner surface of
the eye that consists of photoreceptors and neurons. The retina con-
tains two types of photoreceptors—rods
and cones—which convert light energy to
electrical signals that can be interpreted
by the brain. respond best to dim
light. respond best to bright light
and enable color vision. The retina also
contains many other neurons that process
visual information. The axons of some of
these neurons make up the .
The optic nerve exits through the back of
the eye and runs along the base of the
brain to the thalamus. The thalamus then
relays visual information to the occipital
lobe of the cerebral cortex, where the
information is processed.
optic nerve
Cones
Rods
retina
Optic nerve
Lens
Cornea
Pupil
Iris
Retina
Figure 11 Structure of
eye. Light enters the eye
through the pupil and is
focused on the retina, which
contains photoreceptors.
The blind spot in your visual field corresponds to the site
where the optic nerve exits the back of the eye. There are
no photoreceptors at the site where the optic nerve exits.
Use the procedure below to demonstrate your blind spot.
Demonstrating Your Blind Spot
Procedure
1. On the index card, draw an X
about 1 in. from the left side
of the card. Draw an O about
the same size 3 in. to the
right of the X.
2. Hold your index card in front
of you at arm’s length. Close
your right eye and stare at the
O with your left eye. Slowly
move the card toward you
while continuing to stare at
the O until the X disappears
from view.
Analysis
1. Name the two kinds of
photoreceptors found in
the retina.
2. Propose why you cannot
see images that fall on the
site where the optic nerve
exits the eye.
3. Critical Thinking
Relating Concepts What
is the relationship between
the structure of the retina and
the disappearance of the X on
the index card?
Materials
unlined 3 � 5 index card, pencil
Retina
958
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Demonstration Show the class a chart used to testpeople for colorblindness. Determineif any students are colorblind.Point out that colorblindness iscaused by a chemical disorder inthe cones of the eye. Complete colorblindness is extremely rare. A deficiency in the red or greencones is most common, affectingabout 5 percent of the population.
Visual
Teaching TipMeasuring Sound Play recordedmusic at a volume high enough tobe disconcerting to an average listener. Tell students that the loudness of sound is measured indecibels, ranging from a sound of 0 decibels (dB), which is just audi-ble, to a sound of 140 dB, which ispainful. A jet taking off can pro-duce a sound of 150 dB and causehearing loss. This is why peoplewho work on the tarmac at air-ports wear protective earplugs and headsets.
LS
Chapter 41 • Nervous System 959
did you know?
The “Five” Senses Students have heard ofthe five senses: hearing, smell, taste, sight, andtouch. But these are misleading categories.Touch actually consists of four distinct typesof sensory receptors: hot, cold, pressure, andpain. Another sense, equilibrium or balance, isequally important but not usually discussed interms of the senses. Equilibrium is maintainedthrough fluids in the semicircular canals of theear. Complex sensory organs are responsiblefor some of the senses, such as hearing andsight. Other senses are the result of small clus-ters of receptors, such as taste buds.
When light passes through the lens of an eye, lightwaves are bent and focused on the retina. Review thefollowing properties of light: polarization, reflection,and refraction. Ask students to identify and describewhich property of light occurs as light passes throughthe lens.
Integrating Physics and Chemistry
StrategiesStrategiesINCLUSIONINCLUSION
Working with a partner, have students make observations onsound detection. With the subjectseated and eyes closed, have theother student use a clicker forthe sound test. The studentshould “click” the clicker at dif-ferent points around the studentand record where the subjectdetected the sound origination.After recording observations andswitching roles, students shouldcompare the observation data.They may report their findingsto the class.
• Attention Deficit Disorder• Learning Disability
EarsHow do your ears enable you to hear? Your ears convert the energy
in sound waves to electrical signals that can be interpreted by your
brain. Figure 12 shows the structure of the ear. Sound waves enter
the ear through the ear canal and strike the tympanic (tim PAN ik)
membrane, or eardrum, causing it to vibrate. Behind the eardrum,
three small bones of the middle ear—the hammer, anvil, and
stirrup—transfer the vibrations to a fluid-filled chamber within the
inner ear. This chamber, called the (KAHK lee uh), is coiled
like a snail’s shell, and it contains mechanoreceptors called hair
cells. Hair cells rest on a membrane that vibrates when waves enter
the cochlea. Waves of different frequencies cause different parts of
the membrane to vibrate and thus stimulate different hair cells.
When hair cells are stimulated, they generate nerve impulses in
the auditory nerve. The impulses travel to the brain stem through the
auditory nerve. The thalamus then relays the information to the
temporal lobe of the cerebral cortex, where the auditory information
is processed.
Keeping Your BalanceThe ears not only enable you to hear but also help you maintain equi-
librium. The are fluid-filled chambers in the
inner ear that contain hair cells. Clusters of these hair cells respond
to changes in head position with respect to gravity. When your head
moves, the hair cells are stimulated according to the magnitude and
direction of the fluid’s movement, and they send electrical signals to
the brain. Signals generated by the hair cells enable the brain to
determine the orientation and position of the head.
semicircular canals
cochlea
Figure 12 Structure of ear.
Sound waves are transmitted to
the inner ear and are detected
by mechanoreceptors. The
semicircular canals detect the
position of the head.
Ear
canal
Semicircular
canals
Cochlea
Inner earMiddle ear
Tympanic
membrane
(eardrum)
HammerAnvil
Auditory nerve
Stirrup
Outer ear
The word cochlea is from
the Greek kochlias, meaning
“snail shell.”
959
Copyright © by Holt, Rinehart and Winston. All rights reserved.
ReteachingAssign students to cooperativegroups of four. Have each groupchoose the sensory system theywould least like to lose. Instructeach group to defend its choice.
Quiz1. List the four lobes of the brain.
(occipital, parietal, temporal,frontal)
2.What structures in the ear areresponsible for equilbrium?(semicircular canals)
3. What is a sensory receptor? (aneuron that sends informationfrom the sense organ to the centralnervous system)
AlternativeAssessmentAsk students to prepare a diagramthat traces a sound from its originto the brain. Make sure that stu-dents use the following key termsin their diagram: source, tympanicmembrane, auditory nerve, anvil,stirrup, cochlea, ear canal, tempo-ral region of the cerebral cortex,mechanoreceptors, and hammer.
GENERAL
GENERAL
CloseClose
Answers to Section Review
1. Answers may vary. Sample answers: painreceptors respond to potentially harmful stim-uli; thermo-receptors respond to temperaturechanges; and mechano-receptors respond topressure and tension.
2. Light enters the eye through the pupil. The lensfocuses light on the retina. Rods and cones onthe retina convert light into electrical signalssent along the axons of the optic nerve, whichruns to the thalamus, and finally to the occipi-tal lobe of the cerebrum where the informationis processed.
3. Sound waves enter the ear and strike thetympanic membrane, making it vibrate. The
vibrations pass through the hammer, anvil, andstirrup to the cochlea where mechanoreceptorssend impulses via the auditory nerve to thetemporal lobe of the cerebrum.
4. Chemicals in food are detected by one or moreof four kinds of taste receptors on the tongue.Olfactory receptors bind chemicals in the air.
5. A. Incorrect. Odors are detected by theolfactory receptors. B. Incorrect. The cone cellsdetect colors. C. Correct. The hair cells in thecochlea transfer sound waves into nerveimpulses. D. Incorrect. Tastes are detected bythe taste buds.
960 Chapter 41 • Nervous System
Chemical SensesEmbedded within the surface of the tongue are 2,000–5,000 taste
buds. Most taste buds are located within small projections on the
surface of the tongue. A taste bud, shown in Figure 13, is a cluster
of 50–100 taste cells. Taste cells are chemoreceptors that detect at
least four basic chemical substances: sugars (sweet), acids (sour),
alkaloids (bitter), and salts (salty). Each taste cell is generally sen-
sitive to all tastes but is most sensitive to only one of them. A taste
bud is stimulated when food molecules dissolved in saliva bind to
taste cells. Taste cells generate electrical signals that can be inter-
preted by the brain.
Chemoreceptors that detect odors, called olfactory (ahl FAK tuh
ree) receptors, are located in the roof of the nasal passage. Chemicals
in the air stimulate olfactory receptors, which generate electrical sig-
nals that can be interpreted by the brain. Your sense of smell affects
your enjoyment of food. When you have a bad cold and your nose is
stuffed up, your food may seem to have little taste.
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Topic: Chemical Senses
Keyword: HX4041
Surface of tongue
Taste buds
Sensory
neurons
When food molecules dissolve in
saliva, they enter taste pores and bind
to taste cells.
Taste
poreTaste
cells
A taste bud is a cluster of taste cells surrounding a taste pore.
Figure 13 Location and structure of taste buds
List two different types of sensory receptors andthe kinds of stimuli to which they respond.
Sequence the events that occur when lightenters the eye.
Describe how sound waves are transmittedthrough the ear.
Critical Thinking Comparing Structures
Distinguish between taste cells and olfactoryreceptors.
A person who had defectsin both cochleas likely would be unable to detect
A odors. C sounds.
B colors. D tastes.
Standardized Test PrepStandardized Test Prep
Section 3 Review
960
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section 4
Overview
Before beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section exploresexamples of psychoactive drugs,addiction, and some commonlyabused drugs.
Ask students to list on paper asmany physical and social effects ofsmoking cigarettes as they can.Have them compare their list tothe text on page 965, Effects ofTobacco.
Demonstration
Demonstrate the effect of second-hand smoke. Put several smokingcigarettes in an ashtray. Caution:Burn cigarettes only under a venthood. Place a piece of glassapproximately 5 cm (2 in.) awayfrom the cigarettes. After the ciga-rettes have burned completely,wipe the glass with a white clothand show the cloth to the class.
VisualLS
GENERAL
MotivateMotivate
Bellringer
FocusFocus
Chapter 41 • Nervous System 961
• Directed Reading
• Active Reading GENERAL
Chapter Resource File
• Reading Organizers
• Reading Strategies
• Occupational Applications WorksheetPharmacistForensic Toxicologist GENERAL
Planner CD-ROM
Transparencies
TR Bellringer
Psychoactive DrugsMany different kinds of drugs are available to the public. Adver-
tisements tell you about pain relievers, antacids, cough syrups, and
other medications that can help you feel better. Drugs can prevent,
treat, or cure many different illnesses. However, drugs, whether
legal or illegal, can also be misused or abused.
In the broadest sense, a drug is a chemical that alters body struc-
tures or biological functions. Drugs that alter the functioning of the
central nervous system are known as . Many
medications, such as those prescribed by doctors to treat mental
disorders, contain psychoactive drugs. Caffeine, found in coffee and
soft drinks, is also a psychoactive drug. Alcohol, marijuana, and
cocaine are examples of commonly abused psychoactive drugs. Psy-
choactive drugs also include many other substances, such as
inhalants. Many psychoactive drugs produce physiological depen-
dence and addiction. Abuse of psychoactive drugs can damage the
body, and in some cases, can result in death. Table 3 lists several
classes of commonly abused psychoactive drugs.
psychoactive drugs
Drugs and theNervous System
Section 4
Objectives
● Identify types of psychoac-
tive drugs, and describe their
effects.
● Describe how drug
addiction develops.
● Describe effects of com-
monly abused drugs on the
nervous system.
Key Terms
psychoactive drug
addiction
tolerance
withdrawal
stimulant
depressant
Drug Examples Psychoactive effects Risks associated with use
DepressantsBarbiturates (sedatives), Decreased activity of the Drowsiness, depression, brain or nerve
tranquilizers, alcohol central nervous system damage, coma, respiratory failure
StimulantsCocaine, crack, Increased activity of the Aggressive behavior, paranoia, cardiac
nicotine, amphetamines central nervous system arrest, high blood pressure, brain damage
Nitrous oxide, ether, paint Disorientation, confusion, Brain damage, kidney and liver
Inhalants thinner, glue, cleaning memory loss damage, respiratory failure
fluid, aerosols
LSD, PCP, MDMA (ecstasy), Sensory distortion, anxiety, Depression, paranoia,
Hallucinogens peyote (mescaline),hallucinations, numbness aggressive behavior
psilocybe mushroom
THC Marijuana, hashishShort-term memory loss, Lung damage, loss
impaired judgment of motivation
Heroin, morphine,Feeling of well-being, seda-
Narcoticscodeine, opium
tion, impaired sensory per- Coma, respiratory failure
ception, impaired reflexes
Table 3 Psychoactive Drugs of Abuse
961
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Using the Figure Emphasize that addiction is psy-chological as well as physiological.Ask students to study Figure 15.Have them explain the relationshipbetween the craving for an addic-tive drug and the changes in thenumber of receptor proteins onpostsynaptic cells. Visual
Writing Skills A number ofpotentially addictive substances,including opiates and cocaine, havenow been linked to specific recep-tors in the brain. Have studentsresearch how the work of neuro-chemist Solomon H. Snyder led toa greater understanding of howpotentially addictive substancesaffect the operation of receptors inthe brain. Have students writereports that describe the evidencethat led Snyder to infer the exis-tence of endorphins, the naturallyoccurring opiate-like substances inbrain tissue. VerbalLS
BUILDERSKILL
LS
TeachTeach
962 Chapter 41 • Nervous System
did you know?
Dangerous Street Drugs A street drugcalled “croak” results from the mixture ofmethamphetamines and crack cocaine.Methamphetamines stimulate the release ofnorepinephrine and dopamine. Crack cocaineprevents the reabsorption of dopamine.Extremely high heart rates and blood pressurecan result when large amounts of dopamineenter and remain in synapses. Drug dealersoften mix deadly combinations of drugs tomake more money, to keep the users“hooked,” and in some cases to fool the usersinto thinking they are using a “pure” drug.
Drug Addiction and Neuron Functionis a physiological response caused by use of a drug that
alters the normal functioning of neurons and synapses. Once a
neuron or synapse has been altered by a drug, it cannot function
normally unless the drug is present. With repeated exposure to a
drug, a person addicted to the drug develops tolerance to the drug.
is a characteristic of drug addiction in which increasing
amounts of the drug are needed to achieve the desired sensation.
is a set of emotional and physical symptoms caused by
removal of the drug from the body. The severity of drug addiction is
evident in recovering addicts who experience withdrawal when they
stop taking an addictive drug. Symptoms of withdrawal may include
vomiting, headache, depression, and seizures. Withdrawal from bar-
bituates, and withdrawal in cases of severe alcohol addiction, can
cause death and should be supervised by a doctor.
A Model of Drug AddictionCocaine is a highly addictive stimulant found in the leaves of the
coca plant, Erythroxylon coca, shown in Figure 14. A is a
drug that generally increases the activity of the central nervous sys-
tem. Despite being illegal, cocaine is still used by many people.
Recall that in synaptic transmission, neurotransmitter molecules
are released from a presynaptic neuron and bind to receptor pro-
teins on a postsynaptic cell. Some neurotransmitter molecules are
stimulant
Withdrawal
Tolerance
Addiction
962
BIOgraphic
Action of Cocaine
Cocaine alters the function of dopamine-producing neurons in the limbic system.
Normal synapse
Dopamine is reabsorbed by
the presynaptic neuron.
1 Synapse with cocaine
Cocaine blocks the reabsorption
of dopamine.
2
Dopamine
molecules
Reuptake
receptor
Receptor
protein
Postsynaptic
cell
Presynaptic
neuron
Synaptic
cleft
Ion
channel
Cocaine
molecules
Postsynaptic
membrane
Presynaptic
membrane
Synaptic
vesicles
Figure 14 Coca plant.
Cocaine is derived from the
coca plant, Erythroxylon coca.
Figure 15
962
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Teaching TipEffects of Drugs Have studentschoose a class of frequently abuseddrugs (such as opiates, depressants,or stimulants) or a specific drug(such as cocaine, marijuana, oralcohol). Ask them to make a pam-phlet about the effects of thedrug(s), the dangers of using thedrug(s), and where to seek help fordrug addiction. Verbal
Teaching TipNatural Diuretics Alcohol andcaffeine are diuretics, which causethe excretion of excessive amountsof urine. Alcohol inhibits therelease of antidiuretic hormone.This causes more water to beexcreted in the urine. Caffeinecirculates in the bloodstream to the kidneys where it inhibits thereabsorption of solutes and water.Thus, caffeine also increases urineproduction.
Group Activity Drugs and Their Effects Assignstudents to groups of four. Haveeach group make a table listing different kinds of drugs, theirdesired effects, and their possibleside effects. For each drug listed,have students categorize the drugsas medicinal or social, legal or ille-gal, and prescription or over thecounter. Their tables might includestimulants, depressants, narcotics,hallucinogens, inhalants, hormonereplacements, analgesics, antibi-otics, antihistamines, and appetitesuppressants. Students should findthat many drugs have more sideeffects than desired effects.
Verbal Co-op LearningLS
GENERAL
LS
GENERAL
Chapter 41 • Nervous System 963
Transparencies
TR J76 Psychoactive Drugs of Abuse
TR J74 Action of Cocaine
TR J77 Effects of Blood AlcoholConcentration
reabsorbed by presynaptic neurons after they have been released
into the synaptic cleft. Cocaine is an example of a drug that interferes
with a presynaptic neuron’s ability to reabsorb, or reuptake, neuro-
transmitter molecules. Cocaine affects dopamine (DOH pah meen)
neurons in the limbic system, which plays an important role in the
sensation of pleasure. The mechanism of cocaine action is summa-
rized in Figure 15.
Step At a normal synapse, reuptake receptors move molecules of
dopamine in the synaptic cleft back into the presynaptic
neuron.
Step Cocaine blocks the reuptake of dopamine molecules by
interfering with these reuptake receptors.
Step As a result, excess dopamine remains in the synaptic cleft,
overstimulating the postsynaptic cell. Overstimulation pro-
duces an intense feeling of exhilaration and well-being.
Because the post synaptic cell has been overstimulated, the
number of dopamine receptors will decrease over time.
Step If cocaine is removed from the synaptic cleft, the number
of dopamine molecules returns to normal. This level is now
too low to adequately stimulate the postsynaptic cell
because it has fewer receptor proteins. Addiction occurs
because more cocaine must be taken to maintain adequate
stimulation of the postsynaptic cell.
963
Cocaine removed from synapse
Dopamine release returns to normal, but the
postsynaptic cell is understimulated.
4Overstimulated postsynaptic cell
The number of receptor proteins on the
postsynaptic cell decreases.
3
Postsynaptic
cell
Presynaptic
neuron
Real Life
Caffeine is a stimulant
found in many foods and
beverages.
Chocolate, coffee, tea, and
some soft drinks often
contain caffeine.
Calculating
Make a list of everything
you eat and drink (includ-
ing medicines) for
24 hours; then use a
reference table to
determine your
total caffeine
intake.
963
Copyright © by Holt, Rinehart and Winston. All rights reserved.
DemonstrationShow the class a videotape, in slow motion if possible, of some-one performing a complicated highdive or balance-beam routine.Have students relate this type ofperformance to the function of thecerebellum. Alcohol has a signifi-cant effect on the synapses in thecerebellum. Have students discussalcohol’s effects on balance andcoordination. Interpersonal
Activity BAC Have students research lawsfor blood alcohol concentrationusing the web site in the InternetConnect box on this page. Havestudents write a report summariz-ing their findings. Verbal
DemonstrationInvite a local law enforcementofficer to come to the class todiscuss DUI (Driving Under theInfluence) and DWI (DrivingWhile Intoxicated), incidence ofDUI/DWI, and the dangers ofdrinking and driving. Have theofficer tell students what bloodalcohol concentration is considered“legally drunk” in your state. Havestudents find this BAC level inTable 4.
GENERAL
LS
LS
GENERAL
Teach, continuedTeach, continued
Alcohol Concentration Tell students thatbeer, wine, and liquor differ in their ethanolconcentrations. However, a 12 oz. can of beer,a 4 oz. glass of wine, and a 1 oz. shot ofliquor all contain about the same amount ofabsolute ethanol. Tell students that “proof”reflects the alcohol concentration in a bever-age. Alcohol concentration is determined bydividing the proof number in half—80 proofliquor has a 40 percent alcohol content.
964 Chapter 41 • Nervous System
AlcoholOf all the psychoactive drugs, alcohol (ethanol) is one of the most
widely used and abused. Alcohol, found in wine, beer, and liquor, is
a depressant that produces a sense of well-being when taken in
small amounts. A is a drug that generally decreases the
activity of the central nervous system. As more alcohol is con-
sumed, reaction time increases, and coordination, judgment, and
speech become impaired. This produces a state of intoxication
known as being “drunk.” Drunkenness results as the blood-alcohol
concentration (BAC) increases. BAC can be measured by a breath
test, illustrated in Figure 16, that detects the level of alcohol vapors
in the breath. Table 4 shows the effects of alcohol at various con-
centrations in the blood.
depressant
Table 4 Effects of Blood Alcohol Concentration
BAC* Condition
0.02–0.04 Slight impairment and sedation
0.05–0.06 Slight impairment of coordination; increased reaction time
0.07–0.09 Slurred speech; blurred vision; intoxication
0.10–0.15 Severe intoxication; impaired coordination, vision, and balance
0.15–0.30 Dizziness; confusion; inability to walk; extremely severe intoxication
0.30–0.50 Unconsciousness
0.50–0.60 Coma or death
*in mg of alcohol per mL of blood
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Topic: Blood AlcoholConcentration
Keyword: HX4026
Figure 16 Breath test.
Law enforcement officials use
a device that detects the level
of alcohol vapors in the breath
to estimate the BAC of drunk-
driving suspects.
Alcohol is absorbed into the blood through the stomach and small
intestine. Alcohol affects neurons throughout the nervous system,
changing the shape of receptor proteins. Such widespread changes
in receptor proteins have various effects on normal brain function-
ing.
Addiction to alcohol, or alcoholism, is the most prevalent drug-
abuse problem in the United States. People who drink excessive
amounts of alcohol over long periods of time develop serious health
problems. For example, many alcoholics do not eat properly when
drinking heavily. This can lead to malnutrition, abnormalities in the
circulatory system, and inflammation of the stomach lining. In
addition, the liver begins to use alcohol as an energy source. After
exposure to alcohol over time, the liver accumulates fat deposits. If
drinking of alcohol continues, a potentially fatal liver condition
called cirrhosis (sih ROH sis) may develop. In a cirrhotic liver, cells
are replaced with scar tissue, and liver functioning is impaired.
964
Copyright © by Holt, Rinehart and Winston. All rights reserved.
also adds carbon monoxide to the blood. Thisadded carbon monoxide causes fatty acids tobe deposited on the inside of the arteries andthus is a major contributor to cardiovasculardisease. The combined effect of the strain ofcardiovascular disease and the lack of oxygencontributes heavily to the damage seen insmokers’ cardiovascular systems.
Group Activity Social Drug Use Have studentsbring in newspaper and magazinearticles that deal with smoking cig-arettes and drinking alcohol. Havesome extra articles on hand to useif needed. Assign students togroups of four and ask students toconsider the image of social druguse that is portrayed in the media.Have each group discuss its articleand report back to the class with abrief summary. Display the articleson a bulletin board, and encouragethe class to read them as they studythis section.
Interpersonal Co-op LearningLS
GENERAL
Chapter 41 • Nervous System 965
Nicotine is extremely toxic. In fact, a sulfatederivative of nicotine has been used as acommercial insecticide for years. The lowerdoses of nicotine experienced by smokers arenot immediately noticeable as toxic, however.Initially, nicotine elevates blood pressure byconstricting blood vessels and increasing theheart rate. It stimulates the release of freefatty acids into the bloodstream. Smoking
REAL WORLDREAL WORLDCONNECTIONCONNECTION
Answer
About 90 percent of people whodevelop cancer of the mouth,pharynx, and larynx use tobaccoin some form. Smoking cigarettes,cigars, or pipes is associated withcancers in the mouth, pharynx,larynx, esophagus, and otherorgans. Using smokeless tobaccois associate with cancers of thecheek, gums, and lips.
Source: American Cancer Society
Real Life
NicotineAbout 50 million Americans smoke cigarettes despite convincing
evidence that smoking causes mouth cancer, heart disease, lung
cancer, and emphysema. So why do people continue to smoke?
Many smokers say they would like to stop smoking but find the
habit too difficult to overcome. They are addicted to nicotine, a
drug in cigarette smoke.
Effects of NicotineNicotine is the highly addictive stimulant found in the leaves of the
tobacco plant, Nicotiana tabacum, shown in Figure 17. Nicotine is
extremely toxic; a dose of only 60 mg is lethal in humans. Tobacco
leaves are dried or crushed and are then smoked in cigarettes, cig-
ars, and pipes. Tobacco is also chewed and snuffed.
Nicotine quickly enters the bloodstream and circulates through the
body. In the brain, nicotine mimics the action of the neurotransmit-
ter acetylcholine. Scientists have extensively studied the behavior of
the brain when exposed to nicotine. Nicotine binds to brain cells at
specific sites usually reserved for acetylcholine. These sites are the
central controls of the brain—mechanisms the brain uses to adjust
levels of many of its activities. Like twisting the dial on a central con-
trol, the binding of nicotine to these sites produces many changes.
After a while, the smoker’s body makes adjustments, and systems
almost return to normal—as long as the smoker keeps smoking. Take
away the nicotine, however, and all those adjustments throw every-
thing out of balance all at once. The only way to keep things “normal”
is to keep smoking. The smoker is addicted.
Effects of TobaccoSmokers get more than nicotine from cigarette smoke. Inhaled
smoke contains hundreds of toxic and mutagenic chemicals that
pass through the mouth, air passages, and lungs. These chemicals,
also called tars, are produced by burning tobacco. Because tars and
other chemicals in tobacco smoke are powerful mutagens, smoking
causes lung cancer. Almost all cases of lung cancer, a major cause
of death in the United States, are attributed to smoking.
In the United States, smoking-related illnesses cause more than
400,000 deaths each year. Smoking is associated with cancer of the
mouth and larynx, and smoking may increase the risk of cancer of
the pancreas and bladder. Smoking is also a major contributor to
often-fatal respiratory disorders, such as emphysema. The tars in
smoke irritate mucous membranes in the mouth, nose, and throat.
They accumulate in the lungs and paralyze cilia that move debris
from the lungs. Tars also blacken lung tissue and decrease breath-
ing capacity. People who are exposed to secondhand smoke are at
risk for the same diseases as people who smoke. Women who
smoke during pregnancy are more likely to have miscarriages or to
give birth to stillborn babies.
Real Life
Is smokeless tobacco
harmful?
The use of smokeless
tobacco, such as chewing
tobacco, causes cancers
of the lips, mouth, and
gums. When chewing
tobacco is placed
between the cheek and
gum, nicotine and other
chemicals are absorbed
into the bloodstream.
Finding Information
Find out about mouth
cancers caused by
tobacco.
Figure 17 Tobacco plant.
Tobacco leaves are dried and
crushed and are then smoked
in cigarettes, cigars, and
pipes. Tobacco is also chewed
and snuffed.
965
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Anticipation Guide Ask volun-teers to discuss how their opinionsformed in the Reading Activity onthe opening page of this chapterchanged or stayed the same as aresult of their reading. Studentsshould point to specific passages inthe text that support their reasoning.
Verbal
ReteachingHave students work in pairs. Askeach student to write definitions forthe key terms listed on the firstpage in this section. Ask studentpairs to quiz each other on theterm, and then describe the effectsof psychoactive drugs on the centralnervous system.
Quiz1. Why are pain receptors impor-
tant? (They notify you that bodytissues have been injured.)
2.What is the function of neuro-transmitters? (They transmit nerveimpulses across the synapse.)
3. Compare stimulants withdepressants. (A stimulantgenerally increases the activity of the central nervous system; adepressant generally decreases theactivity.)
AlternativeAssessmentHave students design an informa-tive poster to educate people aboutthe dangers of smoking.
GENERAL
CloseClose
LS
SKILL
BUILDER
READINGREADING
Answers to Section Review
1. Repeated exposure to a drug leads to tolerance,a condition in which increased amounts of thedrug are needed to achieve the desired effect.
2. Cocaine overstimulates postsynaptic neuronsby blocking dopamine reuptake, ultimatelydecreasing the number of dopamine receptors.When cocaine is removed, insufficient dopa-mine is available to stimulate postsynaptic cellsat a normal level.
3. Stimulants, such as nicotine, increase centralnervous system activity. Depressants, such asalcohol, decrease central nervous system activity.
4. All psychoactive drugs alter the function of thecentral nervous system.
5. Addictive drugs alter the normal functioning ofneurons and synapses.
6. A. Correct. It interferes with the presynapticneuron’s ability to reabsorb the neurotransmitter.B. Incorrect. This prevents pain signals fromreaching the brain. C. Incorrect. Sensory percep-tion is everything your senses respond to in theenvironment. D. Incorrect. Synaptic transmissionis the transmission of signals between cells.
966 Chapter 41 • Nervous System
Drugs of AbuseNarcotics are extremely addictive psychoactive drugs that relieve
pain and induce sleep. Some of the most potent narcotics are derived
from the poppy plant, Papaver somniferum, shown in Figure 18. The
sap that oozes from the cut seed pod forms a thick, gummy sub-
stance called opium. Drugs derived from opium, called opiates or
narcotics, include codeine (KOH deen), morphine, and heroin, a more
potent form of morphine. Codeine is widely prescribed by doctors for
pain relief. Morphine is one of the most effective pain-relieving drugs
used today. Heroin addiction and abuse are among the most serious
illegal-drug problems in society.
Recall that pain receptors throughout the body detect painful stim-
uli. As uncomfortable as it may feel, pain plays a very important role
in the body. Pain notifies you that body tissues have been injured or
damaged. Imagine how your body would look and function today if
you did not have the ability to sense pain. Pain begins as a signal at
damaged nerve endings. Nerve impulses generated by pain receptors
travel to the spinal cord toward the brain. After reaching the spinal
cord, a pain signal is suppressed by a class of neurotransmitters called
enkephalins (ihn KEHF uh lihnz). When enkephalins bind to neurons
in the spinal cord, they prevent pain signals from reaching the brain.
Narcotics mimic the action of enkephalins by binding to the same
receptor proteins in the spinal cord. These receptor proteins are
called opiate receptors because scientists observed opiates binding to
them before enkephalins were ever discovered. Narcotics also affect
the limbic system, producing a feeling of well-being.
MarijuanaIn addition to alcohol and tobacco, marijuana, though illegal, is a
widely consumed drug. Marijuana comes from various species of
the hemp plant, Cannabis, shown in Figure 19. Hashish also comes
from the hemp plant. The active ingredient in marijuana and
hashish is commonly known as THC. When marijuana is smoked, it
may cause disorientation, impaired judgment, short-term memory
loss, and general loss of motivation. Scientists continue to research
the effects of THC on the nervous system.
Describe how tolerance to a drug develops.
Summarize how cocaine produces addiction.
Distinguish between stimulants anddepressants. Give an example of each.
Critical Thinking Recognizing
Relationships What do all psychoactive drugs have in common?
Critical Thinking Applying Information
Why is drug addiction considered a physiological condition?
Cocaine interferes withthe normal functions of the limbic system byblocking
A reuptake of dopamine. C sensory perception.
B release of D synaptic enkephalins. transmission.
Standardized Test PrepStandardized Test Prep
Section 4 Review
Figure 18 Opium poppy.
Opium is a narcotic derived
from the poppy plant, Papaver
somniferum.
Figure 19 Hemp. Marijuana
is produced from the hemp
plant, Cannabis.
966
Copyright © by Holt, Rinehart and Winston. All rights reserved.
AlternativeAssessmentDivide the class into four groups ofstudents. Assign one section of thischapter to each group. Tell studentgroups that they are to write a cre-ative poem, short play, or very shortstory (three paragraphs) thatincludes all of the key terms foundin their assigned section. Tell stu-dents that the definitions of eachterm should appear in their writing.When students have completed theircreative writing, ask for volunteersfrom each group to present theirproduct to the rest of the class.
GENERAL
Answer to Concept Map
The following is one of several possible answersto Performance Zone item 15.
Chapter 41 • Nervous System 967
• Science Skills Worksheet
• Critical Thinking Worksheet
• Test Prep Pretest
• Chapter Test GENERAL
GENERAL
GENERAL
Chapter Resource File
has divisions called
is composed of
send signals to
is composed ofis connected to the CNS by
Nervous system
nerves
synapse
neurotransmitters
nerves
spinal cord brain
such as
motor neurons
receive signals from
which travel to the
made of
sensory neurons
using chemicals called
pass signals across
peripheral nervous systemcentral nervous system
neurons
Key Concepts
Study CHAPTER HIGHLIGHTS
ZONE
Neurons and Nerve Impulses
● Neurons are specialized cells that rapidly transmit
information as electrical signals throughout the body.
● At the resting potential, the inside of a neuron is negatively
charged with respect to the outside of the neuron.
● An action potential moves rapidly down an axon.
● Synaptic transmission involves the release of
neurotransmitters at synapses.
Structures of the Nervous System
● The central nervous system consists of the brain and
spinal cord.
● The brain contains three major parts: the cerebrum, the
cerebellum, and the brain stem.
● The spinal cord links the brain to the peripheral nervous
system, which branches throughout the body.
Sensory Systems
● Sensory receptors detect various sensory stimuli.
● Photoreceptors in the eyes convert light into electrical
signals that are interpreted by the brain.
● The ear converts sound into electrical signals that
are interpreted by the brain.
● The semicircular canals monitor the position of
the head.
● Taste and smell are related chemical senses.
Drugs and the Nervous System
● Psychoactive drugs affect the central nervous system.
● Drug addiction involves physiological changes in neurons.
● Alcohol is an addictive depressant that widely affects the
central nervous system.
● Nicotine is an addictive stimulant found in tobacco products.
4
3
2
1
Key Terms
Section 1
neuron (944)
dendrite (944)
axon (944)
nerve (944)
membrane potential (945)
resting potential (946)
action potential (946)
synapse (948)
neurotransmitter (948)
Section 4
psychoactive drug (961)
addiction (962)
tolerance (962)
withdrawal (962)
stimulant (962)
depressant (964)
Section 2
central nervous system (950)
peripheral nervous system (950)
sensory neuron (950)
motor neuron (950)
brain (950)
cerebrum (951)
cerebellum (951)
brain stem (951)
thalamus (952)
hypothalamus (952)
spinal cord (952)
reflex (952)
interneuron (953)
Section 3
sensory receptor (956)
retina (958)
rod (958)
cone (958)
optic nerve (958)
cochlea (959)
semicircular canal (959)
967
Copyright © by Holt, Rinehart and Winston. All rights reserved.
brain. These conflicting signals can causedizziness and vertigo.
12. Cone cells enable color vision. If damage or achemical disorder occurs in these cells, colorblindness could be the result.
Alternative Assessment
13. Sample answer: Alzheimer’s disease: cause:unknown—origin of plaque buildups in thebrain may be neurochemical, environmental,infectious, or genetic; symptoms: impairedmemory, loss of intellectual function, atrophyof brain tissue, degradation of language ability;part of the nervous system: brain; availabletreatment: none available—symptoms are
treated with medication, physical therapy, andoccupational therapy.
968 Chapter 41 • Nervous System
CHAPTER 41
ANSWERS
Understanding Key Ideas
1. c
2. c
3. a
4. b
5. c
6. The fish cerebrum is muchsmaller than a human cerebrum(relative to other parts of thebrain). The sense of smell proba-bly is very important to the fish.
7. Voltage-gate sodium channels,which close shortly after anaction potential, cannot openagain for a brief moment afterthe action potential. This pre-vents the nerve impulse frommoving in the opposite direction.
8. When binding to receptor proteinson the postsynaptic cell, someneurotransmitters cause ion chan-nels to open, some stimulate theformation of second messengers inthe cell, and others stimulateenzyme activity in the cell.
9. Cell-death inhibitors are used formyelin-forming cells. Peripheralnerves are grafted to stimulateaxon growth.
10. One possible answer to the con-cept map is found at the bottomof the previous page.
Critical Thinking
11. The semicircular canals detectacceleration and orientation ofthe body. Eyes detect movement,sending that message to the brain.If the hair cells in the semicircularcanals do not, however, detect thesame degree of movement, theysend a conflicting signal to the
Understanding Key Ideas
1. A myelin sheath on the axon of a neurona. covers the axon completely.b. decreases the rate of impulseconduction.
c. increases the rate of impulseconduction.
d. has no effect on impulse conduction.
2. When a neuron is at the resting potential,a. the inside is positively charged.b. the outside is negatively charged.c. the inside is negatively charged.d. None of the above
3. During an action potential,a. sodium ions flow into a neuron.b. sodium ions flow out of a neuron.c. potassium ions flow into a neuron.d. there is no movement of ions.
4. In a spinal reflex, the signal travelsa. immediately to the brain.b. to the spinal cord and out to a muscle.c. only through sensory neurons.d. only through motor neurons.
5. Drug addiction is considered a physiologicalcondition because addictive drugsa. can be purchased illegally.b. must be injected.c. alter the functioning of neurons.d. are used in social settings.
6. The diagram below shows the brain of afish. How is the cerebrum of the fish braindifferent from that of a human brain? Whatdo the large olfactory bulbs of the fish brainindicate about the relative importance ofthe sense of smell to the fish?
7. Action potentials travel in only one direc-tion along a neuron—toward the axonterminals and away from the cell body.What structures of the neuron ensure that this pattern is always followed?
8. List three ways that the binding of a neurotransmitter to a receptor protein on apostsynaptic cell could cause changes in thecell. (Hint: See Chapter 4, Section 2.)
9. Although neurons in thespinal cord do not grow and regeneratewhen they have been injured, scientists havedeveloped ways to help prevent paralysis.Describe two of these ways.
10. Concept Mapping Make a conceptmap that describes the structures andfunctions of the nervous system. Try toinclude the following terms: spinal cord,brain, neuron, nerve, synapse, andneurotransmitter.
Critical Thinking
11. Inferring Relationships People who sufferfrom vertigo feel dizzy and disoriented incertain situations. What is the relationshipbetween vertigo and the semicircularcanals?
12. Recognizing Relationships Suggest a possi-ble defect of the retina or of retinal cells thatwould cause colorblindness, a condition inwhich a person cannot distinguish betweencertain colors.
Alternative Assessment
13. Summarizing Information Research thecauses and symptoms of various disordersof the nervous system caused by the degen-eration of neurons. Some disorders includeAlzheimer’s disease, Parkinson’s disease,and multiple sclerosis. Find out how thesedisorders affect the nervous system. Listthe types of drugs or other methods used totreat these disorders.
PerformanceZONE
CHAPTER REVIEW
Cerebrum
Olfactory bulbs
968
Section Questions
1 1, 2, 3, 7, 8
2 4, 6, 9, 13
3 11, 12
4 5
Assignment Guide
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Question 2 Answer H is the cor-rect choice. The sodium–potassiumpump helps the neuron achieveresting potential by pumpingsodium ions out of the cell andpotassium ions into the cell.Answer F is incorrect because thenormal resting potential when thepump is working is negative inside.Answer G is incorrect because thefunctioning of voltage-gated ionchannels is not directly related tothe functioning of the sodium–potassium pump. Answer I isincorrect because the normal rest-ing potential of the cell has theseconcentrations, which are main-tained by the sodium–potassiumpump.
Question 4 The muscles that arerigid throughout the body arebeing stimulated by nerveimpulses.
Question 5 Answer H is the cor-rect choice. Drugs may target neu-rotransmitters in order to regulatesensations and moods. Answer F isincorrect because the cerebellumregulates balance, posture, andmovements. Answer G is incorrectbecause motor neurons commandmuscles and organs. Answer I isincorrect because the spinal cordlinks the brain to the peripheralnervous system. None of these islikely to have an effect on a per-son’s emotional state.
Question 6 Answer B is the cor-rect choice. The myelin sheathincreases the speed of actionpotentials. Answer A is incorrectbecause the axon terminal doesnot change the speed. Answer C isincorrect because the axon con-ducts impulses but does notchange their speed. Answer D isincorrect because the dendritereceives impulses but does notchange their speed.
Answers
1. B
2. H
3. A
4. Many muscles are being stimulated at once.
5. H
6. B
Chapter 41 • Nervous System 969
Standardized Test Prep
Understanding ConceptsDirections (1–3): For each question, write ona separate sheet of paper the letter of thecorrect answer.
1 Which of the following is a sensory receptor that is stimulated by light?A. cochlea C. interneuronB. cone D. optic nerve
2 If the sodium–potassium pump of a neuron failed, what effect would this likely have on the neuron’s function?F. The concentrations of positive and negative ions would cause the neuronto be negative inside.
G. Voltage-gated potassium channels andvoltage-gated sodium channels wouldno longer function.
H. The neuron could not conduct anotheraction potential until the resting potential was fully restored.
I. The concentration of sodium ionswould be higher outside the cell andthat of potassium ions would be higherinside.
3 Which part of the ear containsmechanoreceptors?A. cochleaB. eardrumC. hammerD. stirrup
Directions (4): For the following question,write a short response.
4 During an epileptic seizure, many neuronsin the brain produce large bursts of actionpotentials, causing the body to becomerigid and to jerk or convulse. From whatyou know about the brain’s control ofmuscles and posture, how might youexplain these symptoms?
Reading SkillsDirections (5): Read the passage below.Then answer the question.
Depression affects several millionAmericans. Symptoms of depression includewithdrawal, anger, poor communication, sadness, and indifference to surroundings.Depression may be triggered by the loss of afriend or relative, a major disappointmentat work, prescription drugs, prolongedillness, alcohol or drug withdrawal, or hormones. Treatments include counseling,several types of drugs, and exercise.
5 Which structure is likely a target for drugsthat treat depression?F. cerebellumG. motor neuronH. neurotransmitterI. spinal cord
Interpreting GraphicsDirections (6): Base your answer to question6 on the diagram below.
Neuron
6 Which structure increases the speed atwhich the axon conducts action potentials?A. A
B. B
C. C
D. D
Test
When using a diagram to answer a question, look in
the image for evidence that supports your potential
answer.
A
B
C
D
969
Standardized Test Prep
Copyright © by Holt, Rinehart and Winston. All rights reserved.