Embed Size (px)
Citation preview
What You’ll Learn■ You will relate the structure
of a nerve cell to the transmis-sion of a nerve signal.
■ You will identify the sensesand their signal pathways.
■ You will compare and contrast various types ofdrugs and their effects on the nervous system.
Why It’s ImportantYour nervous system helps youperceive and react to the worldaround you. It controls vital involuntary processes such as res-piration and digestion. By under-standing how drugs affect thefunction of the nervous system,you will discover their role intreating medical disorders, andthe danger they pose if misused.
The Nervous SystemThe Nervous System
Visit to• study the entire chapter
online• access Web Links for more
information and activities on the nervous system
• review content with theInteractive Tutor and self-check quizzes
These people feel the tingle offear and excitement when theyrealize the height of the ride.Messages from the brain allowthem to scream or smile as wellas hold on tightly. It is the ner-vous system that interprets thesemessages and coordinates theresponses of the body.
Understandingthe Photo
Rafael Macia/Photo Researchers
942
ca.bdol.glencoe.com
0942-0950 C36S1 BDOL-829900 8/5/04 3:59 AM Page 942
36.1SECTION PREVIEWObjectivesAnalyze how nerve im-pulses travel within thenervous system.Interpret the functions ofthe major parts of the ner-vous system.Compare voluntary re-sponses and involuntaryresponses.
Review Vocabularystimulus: anything in an
organism’s internal orexternal environmentthat causes the organismto react (p. 9)
New Vocabularyneurondendriteaxonsynapseneurotransmittercentral nervous systemperipheral nervous system
cerebrumcerebellummedulla oblongatasomatic nervous systemreflexautonomic nervous systemsympathetic nervous systemparasympathetic nervoussystem
36.1 THE NERVOUS SYSTEM 943
Cellular CommunicationUsing an Analogy When you use the tele-phone you communicate with a person inanother location. You may know that yourmessage is transmitted as an electricalimpulse across telephone wires. Similarelectrical impulses travel throughyour body, allowing some parts tocommunicate with others.Sequence As you read through thissection, record the sequence of changesthat occurs in a neuron when it isexcited by a stimulus.
Aaron Haupt/Photo Researchers
Dendrite
Nucleus
Cell body
Axon
Axonendings
Myelin sheath
Neurons: Basic Units of the Nervous SystemThe basic unit of structure and function in the nervous system is the
neuron, or nerve cell. Neurons (NYU ronz) conduct impulses through-out the nervous system. As shown in Figure 36.1, a neuron is a long cellthat consists of three regions: a cell body, dendrites, and an axon.
Dendrites (DEN drites) are branchlike extensions of the neuron thatreceive impulses and carry them toward the cell body. The axon is an extension of the neuron that carries impulses away from the cell body andtoward other neurons, muscles, or glands.
Neurons fall into three categories: sensory neurons, motor neurons, and interneurons. Sensory neurons carry impulses from the body
to the spinal cord and brain.Interneurons are found within thebrain and spinal cord. They processincoming impulses and pass responseimpulses on to motor neurons. Motorneurons carry the response impulsesaway from the brain and spinal cordto a muscle or gland.
Figure 36.1Dendrites and axons are extensions thatbranch out from the cell body of a neuron.
Like telephone wires between homes, nervecells relay messages within the human body.
The Nervous SystemStandard 9e Students know the roles of
sensory neurons, interneurons, and motor neurons in sensation,thought and response.
California Standards
0942-0950 C36S1 BDOL-829900 8/5/04 4:02 AM Page 943
Relaying an impulseSuppose you’re in a crowded, noisy
store and you feel a tap on yourshoulder. Turning your head, you seethe smiling face of a good friend.How did the shoulder tap get yourattention? The touch stimulated sen-sory receptors located in the skin ofyour shoulder to produce an impulse.The sensory impulse was carried tothe spinal cord and then up to yourbrain. From your brain, an impulsewas sent out to your motor neurons,which then transmitted the impulseto muscles in your neck. Your neckmuscles then turned your head.Figure 36.2 shows how a stimulus,such as a tap on the shoulder, is trans-mitted through your nervous system.
A neuron at restFirst, let’s look at a resting neuron—
one that is not transmitting an impulse.You have learned that the plasma mem-brane controls the concentration ofions in a cell. Because the plasma mem-brane of a neuron is more permeable topotassium ions (K�) than it is tosodium ions (Na�), more potassiumions exist inside of the cell membranethan outside it. Similarly, more sodiumions exist outside the cell membranethan inside of it.
The neuron membrane also con-tains an active transport system, calledthe sodium/potassium (Na�/K�)pump, which uses ATP to pump threesodium ions out of the cell for everytwo potassium ions it pumps in. Asyou can see in Figure 36.3, the actionof the pump increases the concentra-tion of positive charges on the outsideof the membrane. In addition, thepresence of many negatively chargedproteins and organic phosphatesmeans that the inside of the mem-brane is more negatively charged thanthe outside. Under these conditions,which exist when the cell is at rest,
944 THE NERVOUS SYSTEM
Openion channel
Plasma membrane Outside cell
GatedNa� channel
Openion channel
GatedNa� channel
Na�/K�
pump
Inside cell
Figure 36.3In a neuron at rest, the sodium/potassium pump (Na�/K�) and the pres-ence of many negatively charged ions within a cell keeps the inside of acell more negatively charged than the outside.
Receptors in the skinsense a tap or otherstimulus.
A
Sensory neuronstransmit the touchmessage.
B
The message is interpreted by thebrain. A response issent to the motorneurons.
C
Motor neuronstransmit a responsemessage to theneck muscles.
D
The neck muscles areactivated, causing thehead to turn.
E
Figure 36.2The nervous system sorts and interprets incoming information before directing a response.
0942-0950 C36S1 BDOL-829900 8/5/04 4:03 AM Page 944
the plasma membrane is said to bepolarized. A polarized membrane hasthe potential to transmit an impulse.
How an impulse is transmittedWhen a stimulus excites a neuron,
gated sodium channels in the mem-brane open up and sodium ions rushinto the cell. As the positive sodiumions build up inside the membrane,the inside of the cell becomes morepositively charged than the outside.This change in charge, called depo-larization, moves like a wave downthe length of the axon, as seen inFigure 36.4. As the wave passes,gated channels and the Na�/K�
pump act to return the neuron to itsresting state, with the inside of thecell negatively charged and the out-side positively charged.
An impulse can move down thecomplete length of an axon only whenstimulation of the neuron is strongenough. If the threshold level—thelevel at which depolarization occurs—is not reached, the impulse quicklydies out.
Describe the threshold level.
White matter and gray matterMost axons are surrounded by a
white covering of cells called themyelin sheath, shown previously in Figure 36.1. Like the plasticcoating on an electric wire, themyelin sheath insulates the axon,hindering the movement of ionsacross its plasma membrane. Theions move quickly down the axonuntil they reach a gap in the sheath.Here, the ions pass through theplasma membrane of the nerve celland depolarization occurs. As aresult, the impulse jumps from gapto gap, greatly increasing the speedat which it travels.
36.1 THE NERVOUS SYSTEM 945
Na�
Na+
Na�
Gated K� channel
Impulse
Outside cell
Gated Na�
channel Inside cell
K�
Figure 36.4A wave of depolarization moves down the axon of a neuron.
Gated sodium channels open, allowing sodium ions to enterand make the inside of the cell positively charged and the outside negatively charged.
A
Gated K� channel Gated K� channel
Na�
Na�/K�
pumpNa�
K�
K�
Gated Na�
channelGated Na�
channel
Impulse
As the impulse passes, gated sodium channels close, stop-ping the influx of sodium ions. Gated potassium channelsopen, letting potassium ions out of the cell. This actionrepolarizes the cell.
B
Gated K� channel
Na�/K�
pump 2K�
3Na�
Gated Na�
channel
Impulse
As gated potassium channels close, the Na�/K� pump restoresthe ion distribution.
C
0942-0950 C36S1 BDOL-829900 8/5/04 4:03 AM Page 945
The myelin sheath gives axons awhite appearance. In the brain andspinal cord, masses of myelinated axonsmake up what is called “white matter.”The absence of myelin in masses ofneurons accounts for the grayish colorof “gray matter” in the brain.
Connections between neuronsAlthough neurons lie end to end—
axons to dendrites—they don’t actu-ally touch. A tiny space lies betweenone neuron’s axon and another neu-ron’s dendrites. This junction betweenneurons is called a synapse. Impulsestraveling to and from the brain mustmove across the synaptic space thatseparates the axon and dendrites.How do they make this leap?
As an impulse reaches the end of anaxon, calcium channels open, allowingcalcium to enter the end of the axon. Asshown in Figure 36.5, the calciumcauses vesicles in the axon to fuse withthe plasma membrane, releasing theirchemicals into the synaptic space byexocytosis. These chemicals, calledneurotransmitters, diffuse across thespace to the dendrites of the next neu-ron. As the neurotransmitters reach the
dendrites, they signal receptor sites toopen the ion channels. These openchannels change the polarity in theneuron, initiating a new impulse.Enzymes in the synapse typically breakdown the neurotransmitters shortlyafter transmission, preventing the con-tinual firing of impulses.
Explain what prevents the continual firing ofimpulses at the synapse.
The Central NervousSystem
When you make a call to a friend,your call travels through wires to acontrol center where it is switchedover to wires that connect with yourfriend’s telephone. In the same man-ner, an impulse traveling throughneurons in your body usually reachesthe control center of the nervous system—your brain—before beingrerouted. The brain and the spinalcord together make up the centralnervous system, which coordinatesall your body’s activities.
946 THE NERVOUS SYSTEM
Axon
Calciumchannel
Synapse
Synapticspace
Vesicle withneurotransmittersinside
Neurotransmitterdiffuses acrosssynapse and bindswith receptor ondendrite
Vesicle fuseswithmembrane(exocytosis)
Neurotrans-mittersreleased intosynapse
Dendrite
Dendrite
DendriteAxon
Impulse
ImpulseIon channel
Ca2+ Ca2+
Ca2+
AxonFigure 36.5As an impulse reaches theend of an axon, calciumchannels open and calciumenters the end of theaxon. Explain How donerve impulses moveacross a synapse?
AABB
CCDD
PhysicalScience
Connection
Nerve impulsesand parallelcircuits Parallelcircuits containbranched paths inwhich electriccurrent can flow.Connectionsamong neuronsalso can formbranched paths.However, in aparallel circuit, theamount of chargethat flows into andout of a junctionmust be equal.Neurons aredifferent in thatthe strength of theimpulse thatmoves through anexcited neurondoes not dependon the number ofconnections toother neurons.
0942-0950 C36S1 BDOL-829900 8/5/04 4:04 AM Page 946
Two systems work togetherAnother division of your nervous
system, called the peripheral (puhRIH frul) nervous system, is made upof all the nerves that carry messages toand from the central nervous system.It is similar to the telephone wires thatrun between a phone system’s controlcenter and the phones in individualhomes. Together, the central nervoussystem (CNS) and the peripheralnervous system (PNS), shown inFigure 36.6, respond to stimuli fromthe external environment.
Anatomy of the brainThe brain is the control center of
the entire nervous system. Fordescriptive purposes, it is useful todivide the brain into three main sec-tions: the cerebrum, the cerebellum,and the brain stem.
The cerebrum (suh REE brum) isdivided into two halves, called hemi-spheres, that are connected by bundlesof nerves. Your conscious activities,intelligence, memory, language, skele-tal muscle movements, and senses areall controlled by the cerebrum. Theouter surface of the cerebrum, calledthe cerebral cortex, is made up of graymatter. The cerebral cortex containscountless folds and grooves thatincrease its total surface area. Thisincrease in surface area played animportant role in the evolution ofhuman intelligence as greater surfacearea allowed more and more complexthought processes.
The cerebellum (ser uh BE lum),located at the back of your brain, con-trols your balance, posture, and coor-dination. If the cerebellum is injured,your movements become jerky.
The brain stem is made up of themedulla oblongata, the pons, and themidbrain. The medulla oblongata(muh DU luh • ah blon GAH tuh) is the
part of the brain that controls involun-tary activities such as breathing andheart rate. The pons and midbrain actas pathways connecting various parts ofthe brain with each other. Read moreabout how the brain evolved on pages1090–1091 in the Focus On. For the lat-est on technological advances in brainimaging, check out the Biotechnologysection at the end of the chapter.
36.1 THE NERVOUS SYSTEM 947
Brain
Spinalcord
Medulla oblongataCerebellum
CerebrumSkull
Vertebra
Spinal cord
Figure 36.6The human nervous system is madeup of the CNS, in pink, and the PNS,in yellow. The brain and spinal cordare protected by the skull and thevertebrae, respectively.
0942-0950 C36S1 BDOL-829900 8/5/04 4:04 AM Page 947
The Peripheral Nervous System
Remember that the peripheral ner-vous system carries impulses betweenthe body and the central nervous sys-tem. For example, when a stimulus ispicked up by receptors in your skin, itinitiates an impulse in the sensory
neurons. The impulse is carried to theCNS. There, the impulse transfers tomotor neurons that carry the impulseto a muscle.
The peripheral nervous system canbe separated into two divisions—thesomatic nervous system and the auto-nomic nervous system.
The somatic nervous systemThe somatic nervous system is
made up of 12 pairs of cranial nervesfrom the brain, 31 pairs of spinalnerves from the spinal cord, and all oftheir branches. These nerves are actu-ally bundles of neuron axons boundtogether by connective tissue. Thecell bodies of the neurons are foundin clusters along the spinal column.
The nerves of the somatic system arepart of the peripheral nervous systemthat relays information between yourCNS and skeletal muscles. A responseby the somatic nervous system to astimulus usually is voluntary, meaningthat you can decide whether or not tomove body parts under the control ofthis system. Try the MiniLab on thispage to find out how distractions canaffect the time it takes you to respondto a stimulus.
Reflexes in the somatic systemSometimes a stimulus results in
an automatic, unconscious responsewithin the somatic system. When youtouch something hot, you automati-cally jerk your hand away. Such anaction is a reflex, an automaticresponse to a stimulus. Rather thanproceeding to the cerebrum or cerebel-lum for interpretation, a reflex impulsetravels to the spinal column or brainstem where it causes an impulse to besent directly back to a muscle. Thebrain becomes aware of the reflex onlyafter it occurs. Figure 36.7 on the nextpage shows the shortened route of areflex impulse.
948 THE NERVOUS SYSTEMMatt Meadows
ExperimentDistractions and ReactionTime Have you ever tried toread while someone is talking toyou? What effect does such a dis-tracting stimulus have on yourreaction time?
Procedure! Work with a partner. Sit
facing your partner as he orshe stands.
@ Have your partner hold thetop of a meterstick aboveyour hand. Hold your thumband index finger about 2.5 cm away from either side ofthe lower end of the meterstick without touching it.
# Tell your partner to drop the meterstick straight downbetween your fingers.
$ Catch the meterstick between your thumb and finger assoon as it begins to fall. Measure how far it falls beforeyou catch it. Practice several times.
% Run ten trials, recording the number of centimeters themeterstick drops each time. Average the results.
^ Repeat the experiment, this time counting backwards from100 by fives (100, 95, 90, . . .) as you wait for your partnerto release the meterstick.
Analysis1. Analyze Did your reaction time improve with practice?2. Evaluate How was your reaction time affected by the
distraction (counting backwards)?3. Infer What other factors, besides distractions, would
increase reaction time?
0942-0950 C36S1 BDOL-829900 8/5/04 4:05 AM Page 948
949R. Andrew Odum/Peter Arnold, Inc.
Motorneuron
Interneuron
Spinalcord
Flexor muscle contracts and withdraws part being stimulated
Sensory neuron
Direction of impulse
Pain receptors in skin
Figure 36.7A simple reflex impulseinvolves one sensory neu-ron, one interneuron, andone motor neuron.
The autonomic nervous systemImagine that you are spending the
night alone in a creepy old house.Suddenly, a creak comes from theattic and you think you hear foot-steps. Your heart begins to pound.Your breathing becomes rapid. Yourthoughts race wildly as you try to figureout what to do—stay and confront theunknown, or run out of the house!
Your internal reactions to this scarysituation are being controlled by your autonomic nervous system. Theautonomic nervous system carriesimpulses from the CNS to internalorgans. These impulses produce re-sponses that are involuntary, or notunder conscious control.
There are two divisions of theautonomic nervous system—the sympathetic nervous system andthe parasympathetic nervous system.The sympathetic nervous system controls many internal functions during times of stress. When some-thing frightens you, such as therattlesnake shown in Figure 36.8,
the sympathetic nervous system causes the release ofhormones, such as epinephrineand norepinephrine, that resultsin the fight-or-flight response.
The parasympathetic nervous system on the other hand, controlsmany of the body’s internal functionswhen it is at rest. It is in control whenyou are relaxing after a picnic or read-ing quietly in your room. Both thesympathetic and parasympathetic sys-tems send signals to the same internalorgans. The resulting activity of theorgan depends on the intensities of theopposing signals.
Figure 36.8A fight-or-flightresponse to a rattle-snake will increaseheart and breathingrates.
0942-0950 C36S1 BDOL-829900 8/5/04 4:06 AM Page 949
The different divisions and subsys-tems of your nervous system are sum-marized in Figure 36.9. Each divisionplays a key role in communicationand control within your body.
Note that the sympathetic andparasympathetic systems are part of
the autonomic nervous system. Theautonomic and somatic systems arepart of the PNS. The peripheral ner-vous system carries information to andfrom the CNS. Together, these twosystems respond to stimuli from theexternal and internal environment.
Understanding Main Ideas1. Summarize how nerve impulses travel within the
nervous system.
2. Interpret and compare the functions of the centraland peripheral nervous systems.
3. Interpret the functions of the three major parts ofthe brain.
4. Compare and contrast voluntary responses andinvoluntary responses.
Thinking Critically5. Why is it nearly impossible to stop a reflex from
taking place?
6. Get the Big Picture Compare the interrelation-ships between the nervous system and other bodysystems in response to an external stimulus. Formore help, refer to Get the Big Picture in the Skill Handbook.
SKILL REVIEWSKILL REVIEW
950 THE NERVOUS SYSTEM
CentralNervousSystem(CNS)
SomaticNervousSystem
(voluntary)
Relays informationto skeletal muscles.
AutonomicNervousSystem
(involuntary)
Relays informationto internal organs.
Sympathetic NervousSystem
Controls organs in times of stress.
Parasympathetic NervousSystem
Controls organs when body is at rest.
PeripheralNervousSystem(PNS)
Nervous System
Figure 36.9Understanding the organization ofyour nervous system can be madeeasier by studying the differentdivisions of the nervous system.
ca.bdol.glencoe.com/self_check_quiz
0942-0950 C36S1 BDOL-829900 8/5/04 4:06 AM Page 950
Sensing ChemicalsHow are you able to smell and taste
an orange? Chemical molecules of theorange contact receptors in your nose andmouth as you sniff and eat the fruit. Thereceptors for smell are hairlike nerve end-ings located in the upper portion of yournose, as shown in Figure 36.10. Chemicalsacting on these nerve endings initiateimpulses in the olfactory nerve, which isconnected to your brain. In the brain, thissignal is interpreted as a particular odor.
The senses of taste and smell are closelylinked. Think about what your sense oftaste is like when your nose is stuffed upand you can smell little, if anything.Because much of what you taste dependson your sense of smell, your sense of tastemay also be dulled.
36.2 THE SENSES 951
Olfactory nerve
Smell moleculesTaste molecules
Olfactory bulb
Olfactory nerve receptors
Taste bud
Sensory neuron
Figure 36.10Chemicals stimulate bothsmell and taste receptors.
The Senses
SECTION PREVIEWObjectivesDefine the role of thesenses in the human ner-vous system.Recognize how sensesdetect chemical, light, andmechanical stimulation.Identify ways in which thesenses work together togather information.
Review Vocabularydermis: inner, thicker
portion of the skin thatcontains nerves andnerve endings (p. 895)
New Vocabularytaste budretinarodconecochleasemicircular canals
36.2
Read for Main Ideas As you read Chapter 36, record under the appropriate tab each process by which your body responds to stimuli.
Fold a vertical sheet of paper from side to side. Make the back edge about 5cm longer than the front edge.
Turn lengthwise and fold into thirds, then fold again in half to make sixths.
Unfold and cut only the top layer along the five folds to make six tabs.
Label each tab asfollows: Smell, Taste, Sight, Hearing, Balance and Touch. Label the top edge as Senses.
The Senses Make the following Foldable to help you organize information about the senses.
STEP 1
STEP 3
STEP 2
STEP 4
Standard 9b Students know how the nervous system mediates communicationbetween different parts of the body and the body’s interactions with the environment.
California Standards
0951-0955 C36S2 BDOL-829900 8/5/04 4:19 AM Page 951
You taste something when chemi-cals dissolved in saliva contact sensoryreceptors on your tongue called tastebuds. Tastes that you experience canbe divided into four basic categories:sour, salty, bitter, and sweet. As seenwith the sequence of electrochemicalchanges a neuron undergoes as it isdepolarized, each of the differenttastes produces a similar change inthe cells of taste buds. As these cellsare depolarized, signals from yourtaste buds are sent to the cerebrum.There, the signal is interpreted andyou notice a particular taste. A youngadult has approximately 10 000 tastebuds. As a person ages, his or hersense of smell becomes less sharp andtaste buds may decrease in number orbecome less sensitive. This can resultin a decreased sense of taste.
Sensing LightHow are you able to see? Your sense
of sight depends on receptors in youreyes that respond to light energy. Theretina, found at the back of the eye, isa thin layer of tissue made up of light
receptors and sensory neurons. Lightenters the eye through the pupil and isfocused by the lens onto the back ofthe eye, where it strikes the retina.Follow the pathway of light to theretina in Figure 36.11.
The retina contains two types oflight receptor cells—rods and cones.Rods are receptor cells adapted forvision in dim light. They help youdetect shape and movement. Conesare receptor cells adapted for sharpvision in bright light. They also helpyou detect color.
At the back of the eye, retinal tissuecomes together to form the opticnerve, which leads to the brain, whereimages are interpreted. Can you see aswell with one eye as with two? To findout more about how the brain forms avisual image, look at Figure 36.12.
Compare and contrast rods and cones.
Sensing MechanicalStimulation
How are you able to hear the leavesrustle and feel the grass as you relax inthe park? These senses, hearing andtouch, depend on receptors thatrespond to mechanical stimulation.
Your sense of hearingEvery sound causes the air around it
to vibrate. These vibrations travel out-ward from the source in waves, calledsound waves. Sound waves enter yourouter ear and travel down to the endof the ear canal, where they strike amembrane called the eardrum andcause it to vibrate. The vibrations thenpass to three small bones in the mid-dle ear—the malleus, the incus, andthe stapes. As the stapes vibrates, itcauses the membrane of the oval win-dow, a structure between the middleand inner ear, to move back and forth.
Retina
Choroid
Sclera
Optic nerve
Light
Cornea
Pupil
Lens
Iris
Figure 36.11A cross section throughthe human eye showsthe path light takes asit enters through thepupil.
952 THE NERVOUS SYSTEM
PhysicalScience
Connection
Levers The bonesof the inner earamplify the inputforce applied onthem by theeardrum. Themalleus and incustogether act as alever, and applythe output forceto the stapes.Here, themechanicaladvantage, whichis the output forcedivided by theinput force, isabout 1.3. Howmuch larger is theoutput force thanthe input force?
0951-0955 C36S2 BDOL-829900 8/5/04 4:20 AM Page 952
The EyeFigure 36.12The light energy that reaches your retina is converted into nerveimpulses, which are interpreted by your brain, allowing you tosee the world around you. Critical Thinking How would a person’s vision be affected if his or her rod cells didn’tfunction?
36.2 THE SENSES 953
Lens
Retina
Optic nerve
Visual cortexin cerebrum
Top view of brain
Visual field Close one eye. Everything you cansee with one eye open is the visual field of thateye. The visual field of each eye can be divided intotwo parts: a lateral, or outer portion, and a medial,or inner portion. As shown, the lateral half of thevisual field projects onto the medial portion of theretina, and the medial half of the visual fieldprojects onto the lateral portion of the retina.
BB
Brain image projections The right half ofthe retina in each eye is connected to the rightside of the visual cortex in the cerebrum. The lefthalf of the retina is similarly connected to the leftside of the visual cortex. Thus images entering theeye from the right half of each visual field projectto the left half of the brain, and vice versa.
DD
Rod and cone cells
Color-enhanced SEMMagnification: 500�
Depth perception The visualfields of the eyes partially overlap,each eye seeing about two-thirdsof the total field. This overlapallows your brain to judge thedepth of your visual field.
CC
Rod and cone cells Rod cells inthe retina are excited by low levels oflight. These cells convert light signalsinto nerve impulses and relay them tothe brain. Your brain interprets theinformation as a black and whitepicture. Your cone cells respond tobright light. They provide the brainwith information about color.
AA
CNRI/Science Photo Library/Photo Researchers
0951-0955 C36S2 BDOL-829900 8/5/04 4:21 AM Page 953
From here, the vibrations continue totravel deeper into the ear. The move-ment from the oval window causesfluid in the cochlea, a snail-shapedstructure in the inner ear, to move.Inside the circular walls of the cochleaare structures that are lined with haircells. The fluid in the cochlea moveslike a wave against the hair cells causingthem to bend.
The movement of the hairs pro-duces electrical impulses, whichtravel along the auditory nerve to thesides of the cerebrum, where they areinterpreted as sound. Trace the path-way of sound waves in Figure 36.13.Hearing loss can occur if the auditorynerve or the hair cells in the cochleaare damaged. To find out whatimpact loud sounds have on yourhearing, do the Problem-Solving Labon this page.
Your sense of balanceThe inner ear also converts infor-
mation about the position of yourhead into nerve impulses which travelto your brain, informing it about yourbody’s equilibrium.
Maintaining balance is the functionof your semicircular canals. Like thecochlea, the semicircular canals are alsofilled with a thick fluid and lined with
954
Figure 36.13The internal structure ofthe human ear is dividedinto three areas: theouter ear, middle ear,and inner ear. Followthe pathway soundwaves take as they move through your ear.
Ear canal
Eardrum
Malleus Incus Stapes
Oval window
Semicircular canals
Cochlea
Inner earMiddle earOuter ear
Auditory nerve
Interpret and AnalyzeWhen are loud sounds dangerous to our hearing? Obser-vations may be described as either qualitative or quantitative.A qualitative observation about a woman’s height might bethat she is tall. A quantitative observation about the same person might be that she is 1.92 m tall.
Solve the Problem“Hearing loss afflicts approximately 28 million people in theUnited States. Approximately 10 million of these impairmentsmay be partially attributable to damage from exposure to loud sounds. Sounds that are sufficiently loud to damage sensitive inner ear structures can produce hearing loss that isnot reversible. Very loud sounds of short duration, such as anexplosion or gunfire, can produce immediate, severe, and per-manent loss of hearing. Longer exposure to less intense butstill hazardous sounds encountered in the workplace or duringleisure activities, exacts a gradual toll on hearing sensitivity,initially without the victim’s awareness. Live or recorded high-volume music, lawn-care equipment, and airplanes are exam-ples of potentially hazardous noise.”
—“Noise and Hearing Loss,” NIH Consensus Statement,January 22–24, 1990
Thinking Critically1. Analyze Choose and record two sentences or phrases
from the passage above that provide examples of quanti-tative observations. Explain your selections.
2. Analyze Choose and record two sentences or phrases that provide examples of qualitative observations. Explain yourselections.
3. Infer Choose and record one sentence or phrase that pro-vides an example of an inference. Explain your selection.
4. Think Critically Suggest ways to minimize the type ofnoise exposure discussed in the last sentence.
0951-0955 C36S2 BDOL-829900 8/5/04 4:22 AM Page 954
hair cells. When you tilt your head, thefluid moves, causing the hairs to bend.This movement stimulates the haircells to produce impulses. Neuronsfrom the semicircular canals carry theimpulses to the brain, which sends animpulse to stimulate your neck musclesand readjust the position of your head.
Explain the functionof the semicircular canals.
Your sense of touchLike the ear, your skin also re-
sponds to mechanical stimulationwith receptors that convert the stimu-lus into a nerve impulse. Receptors inthe dermis of the skin respond tochanges in temperature, pressure, andpain. It is with the help of thesereceptors, shown in Figure 36.14,that your body is able to respond toits external environment.
Although some receptors are foundall over your body, those responsiblefor responding to particular stimuli areusually concentrated within certainareas of your body. For example, recep-tors that respond to light pressure arenumerous in the dermis of your finger-tips, eyelids, lips, the tip of yourtongue, and the palms of your hands.When these receptors are stimulated,you perceive sensations of light touch.
Receptors that respond to heavierpressure are found inside your joints,in muscle tissue, and in certain
organs. They are also abundant onthe skin of your palms and fingers andon the soles of your feet. When thesereceptors are stimulated, you perceiveheavy pressure.
Free nerve endings extend into thelower layers of the epidermis. Freenerve endings act as receptors foritch, tickle, hot and cold, and painsensations. Heat receptors are founddeep in the dermis, while cold recep-tors are found closer to the surface ofyour skin. Pain receptors can befound in all tissues of the body exceptthose in the brain.
Understanding Main Ideas1. Summarize the different types of messages the
senses receive.
2. When you have a cold, why is it difficult to tastefood?
3. Explain how your eyes detect light and images.
4. List the different types of receptors that are foundin the skin.
Thinking Critically5. Why might an ear infection lead to problems with
balance?
6. Sequence List the sequence of structuresthrough which sound waves pass to reach theauditory nerve. For more help, refer to Sequencein the Skill Handbook.
SKILL REVIEWSKILL REVIEW
36.2 THE SENSES 955
Hairshaft
Free nerveending
Heat
Heavypressure
Cold
Lighttouch
Opening ofsweat gland
Figure 36.14Many kinds of receptorsare located throughoutthe skin. Describe Whattypes of sensationsare perceived whenthe different recep-tors are stimulated?
ca.bdol.glencoe.com/self_check_quiz
0951-0955 C36S2 BDOL-829900 8/5/04 4:22 AM Page 955
36.3SECTION PREVIEWObjectivesRecognize the medicinaluses of drugs.Identify the differentclasses of drugs.Interpret the effects ofdrug misuse and abuse onthe body.
Review Vocabularyreceptors: specific binding
sites found on the surfaceof or within a cell (p. 930)
New Vocabularydrugnarcoticstimulantdepressantaddictiontolerancewithdrawalhallucinogen
Drugs and the Nervous SystemFinding Main Ideas On a piece ofpaper, construct an outline about theeffects of drugs on the nervous sys-tem. Use the red and blue titles in thesection as a guideline. As you read theparagraphs that follow the titles, addimportant information and vocabularywords to your outline.
Example:I. Drugs act on the body
A. Drugs affect body functionsII. Medicinal uses of drugs
A. Relieving Pain1. Narcotics
Use your outline to help you answerquestions in the Section Assessmenton page 963. For more help, refer to Outline in the Skill Handbook.
Drugs Act on the BodyYou probably hear the word drug used
often, maybe even every day. A drug is achemical that affects the body’s func-tions. Most drugs interact with receptorsites on cells, probably the same onesused by neurotransmitters of the ner-vous system or hormones of the endo-crine system. Some drugs increase therate at which neurotransmitters are syn-thesized and released, or slow the rate atwhich they are broken down, as illus-trated in Figure 36.15. Other drugsinterfere with a neurotransmitter’s abil-ity to interact with its receptor. Explorehow these different drugs work on neu-rotransmitters by doing the Problem-Solving Lab on the next page.
The Effects of Drugs
Tobacco leaves, used to make cigarettes,contain the addictive drug nicotine.
Synaptic space
Increasedrelease
Decreasedenzymaticbreakdown
Dendrite
AxonIncreasedsynthesis
Figure 36.15Drugs can increase neurotransmitter levels in the synapseby stimulating their synthesis, increasing their release, orby slowing their breakdown by enzymes.
956Adam Jones/Photo Researchers
0956-0969 C36S3 BDOL-829900 8/5/04 4:31 AM Page 956
36.3 THE EFFECTS OF DRUGS 957
Medicinal Uses of Drugs
A medicine is a drug that, whentaken into the body, helps prevent,cure, or relieve a medical problem.Some of the many kinds of medicinesused to relieve medical conditions arediscussed below.
Relieving painHeadache, muscle ache, cramps—
all are common pain sensations. Youjust studied how pain receptors inyour body send signals to your brain.Medicines that relieve pain manipu-late either the receptors that initiatethe impulses or the central nervoussystem that receives them.
Pain relievers that do not cause aloss of consciousness are called anal-gesics. Some analgesics, like aspirin,work by inhibiting receptors at thesite of pain from producing nerveimpulses. Analgesics that work onthe central nervous system are called narcotics. Many narcotics are madefrom the opium poppy flower,shown in Figure 36.16. Opiates, asthey are called, can be useful in controlled medical therapy becausethese drugs are able to relieve severepain from illness or injury.
Describe how medi-cines that relieve pain work.
Formulate ModelsHow do different drugs affect the levels of neurotrans-mitters in synapses? Drugs can act on neurotransmitters ina number of different ways. For example, they may block therelease of the neurotransmitter from the axon of a neuron.They may also prevent the breakdown of the neurotransmitterby blocking the enzyme responsible for this action.
Solve the ProblemExamine the diagram shown here, which illustrates how neurotransmitters work.
Thinking Critically 1. Formulate Models Draw models for two different drugs:
a. Illustrate a drug that could block the enzyme frombreaking down the neurotransmitter.
b. Illustrate a drug that could block the release of the neurotransmitter from the axon.
2. Evaluate Evaluate your models according to their adequacy in representing the effects a drug can have on the transmission of an impulse across a synapse.
3. Predict Predict the effects of each drug on the body.
Robert Lyons/Visuals Unlimited
Figure 36.16Sticky sap from the fruit of anopium poppy is used to makedrugs called opiates.
Axon
Dendrite
Enzyme Neurotransmitter
0956-0969 C36S3 BDOL-829900 8/5/04 4:33 AM Page 957
Treating circulatory problemsMany drugs have been developed to
treat heart and circulatory problemssuch as high blood pressure. Thesemedicines are called cardiovasculardrugs. In addition to treating highblood pressure, cardiovascular drugsmay be used to normalize an irregularheartbeat, increase the heart’s pumpingcapacity, or enlarge small blood vessels.Discover how various types of drugscan affect heart rate by doing theBioLab at the end of this chapter.
Treating nervous disordersSeveral kinds of medicines are used
to help relieve symptoms of nervoussystem problems. Among these medi-cines are stimulants and depressants.
Drugs that increase the activity of the central and sympathetic ner-vous systems are called stimulants.
Amphetamines (am FE tuh meenz) aresynthetic stimulants that increase theoutput of CNS neurotransmitters.Amphetamines are seldom prescribedbecause they can lead to dependence.However, because they increasewakefulness and alertness, ampheta-mines are sometimes used to treatpatients with sleep disorders.
Drugs that lower, or depress, theactivity of the nervous system are calleddepressants, or sedatives. The pri-mary medicinal uses of depressants areto encourage calmness and producesleep. For some people, the symptomsof anxiety are so extreme that theyinterfere with the person’s ability tofunction effectively. By slowing downthe activities of the CNS, a depressantcan temporarily relieve some of thisanxiety.
The Misuse and Abuseof Drugs
The misuse or abuse of drugs cancause serious health problems—evendeath. Drug misuse occurs when amedicine is taken for an unintendeduse. For example, giving your prescrip-tion medicine to someone else, not fol-lowing the prescribed dosage by takingtoo much or too little, and mixingmedicines, are all instances of drugmisuse. You must pay careful attentionto the specific instructions given on thelabel of a drug you are taking. TheMiniLab on the next page shows youhow to analyze such a label.
Drug abuse is the inappropriateself-administration of a drug for non-medical purposes. Drug abuse mayinvolve use of an illegal drug, such ascocaine; use of an illegally obtainedmedicine, such as someone else’s pre-scribed drugs; or excessive use of alegal drug, such as alcohol or nico-tine. Drugs abused in this way can
958 THE NERVOUS SYSTEM
cardiovascularfrom the Greekword kardia, mean-ing “the heart,”and the Latin wordvasculum, meaning“small vessel”; Car-diovascular drugstreat problemsassociated withblood vessels of the heart.
Will & Deni McIntyre/Photo Researchers
Pharmacist
Would you like to help peoplecontrol or recover from
illness by dispensing the latestmedications developed throughbiotechnology? Then consider acareer as a pharmacist.
Skills for the JobPharmacists read prescriptions writ-
ten by doctors and other health profes-sionals and carefully prepare containers with the correctmedicine. (Few pharmacists still mix the medicine them-selves; that is done by the drug manufacturer.) Pharmacistsmust know how drugs interact and guide people in avoid-ing harmful combinations. Besides drugstores, pharmacistswork in hospitals and nursing homes, and for drug compa-nies and government agencies. To become a pharmacist,you must complete a five-year bachelor’s degree in phar-macy and pass a state examination.
For more careers in related fields, visitca.bdol.glencoe.com/careers
0956-0969 C36S3 BDOL-829900 8/5/04 4:34 AM Page 958
have powerful effects on the nervoussystem and other systems of the body,as described in Figure 36.17.
Addiction to drugsWhen a person believes he or she
needs a drug in order to feel good orfunction normally, that person is psy-chologically dependent on the drug.When a person’s body develops achemical need for the drug in order tofunction normally, the person is phys-iologically dependent. Psychologicaland physiological dependence areboth forms of addiction.
Tolerance and withdrawalWhen a drug user experiences tol-
erance to or withdrawal from a fre-quently used drug, that person isaddicted to the drug. Toleranceoccurs when a person needs larger ormore frequent doses of a drug toachieve the same effect. The dosageincreases are necessary because thebody becomes less responsive to the drug. Withdrawal occurs whenthe person stops taking the drug andactually becomes ill.
(l)Lawrence Migdale/Photo Researchers, (r)Matt Meadows
36.3 THE EFFECTS OF DRUGS 959
Figure 36.17The use of anabolic steroids without carefulguidance from a physician is illegal. Some dangerous side effects of steroid abuse include cardiovascular disease, kidney damage, and cancer.
Analyze InformationInterpret a Drug Label One common misuse of drugs is notfollowing the instructions that accompany them. Over-the-counter medicines can be harmful—even fatal—if they are notused as directed. The Food and Drug Administration requiresthat certain information about a drug be provided on its labelto help the consumer use the medicine properly and safely.
Procedure! The photograph below shows a label from an over-the-
counter drug. Read it carefully.@ Make a data table like the one shown. Then fill in the
table using information on the label.
Analysis1. Evaluate Evaluate the promotional claims on this prod-
uct’s label. What symptoms will this product relieve? Whatside effects can result from using this product? Is this prod-uct appropriate for everyone to use?
2. Infer Why should a person never take more than the recommended dosage?
People with these condi-tions should avoid this drug
CorrectDosage
SymptomsThis Drug
WillRelieve
This drugshould notbe taken
with thesemedicines
PossibleSide
Effects
Information from a Drug Label
0956-0969 C36S3 BDOL-829900 8/5/04 4:35 AM Page 959
Classes of CommonlyAbused Drugs
Each class of drug produces its ownspecial effect on the body, and its ownparticular symptoms of withdrawal.Table 36.1 summarizes the healtheffects of some commonly abuseddrugs.
Stimulants: Cocaine,amphetamines, caffeine, and nicotine
You already know that stimulantsincrease the activity of the central ner-vous system and the sympathetic ner-vous system. Increased CNS stimula-tion can result in mild elevation ofalertness, increased nervousness, anxi-ety, or even convulsions.
Cocaine stimulates the CNS byworking on the part of the inner brainthat governs emotions and basicdrives, such as hunger and thirst.When these needs are met under nor-mal circumstances, neurotransmit-ters—such as dopamine—are releasedto reward centers and the person expe-riences pleasure. Cocaine artificiallyincreases levels of these neurotrans-mitters in the brain. As a result, falsemessages are sent to reward centersindicating that a basic drive has beensatisfied. The user quickly feels aeuphoric high called a rush. Thissense of intense pleasure and satis-faction cannot be maintained,however, and soon the effectsof the drug change. Physicalhyperactivity follows. Often,anxiety and depression set in.
Cocaine also disrupts the body’scirculatory system by interfering withthe sympathetic nervous system. Although initially causing a slowingof the heart rate, it soon produces agreat increase in heart rate and a narrowing of blood vessels, known as vasoconstriction. The result is high blood pressure. Heavy use ofthis drug compromises the immune system and often leads to heart ab-normalities. Cocaine may affect morethan just the individual who uses it.As Figure 36.18 shows, babies of ad-dicted mothers are sometimes bornalready dependent on this drug.
Amphetamines are stimulants thatincrease levels of CNS neurotransmit-ters. Like cocaine, amphetamines alsocause vasoconstriction, a racing heart,and increased blood pressure. Otheradverse side effects of amphetamineabuse include irregular heartbeat,chest pain, paranoia, hallucinations,and convulsions.
Not all stimulants are illegal. Asshown in Figure 36.19, one stimu-lant in particular is as close as the near-est coffee maker or candy machine.Caffeine—a substance found in coffee,some carbonated soft drinks, cocoa,
(t)Henley & Savage/The Stock Market, (b)Matt Meadows,
Figure 36.18Babies born addicted to crack cocaine areusually low in birthweight, continually irritable, and mayshake constantly.
960 THE NERVOUS SYSTEM
Figure 36.19Caffeine can trigger a con-dition called tachycardia,when the heart beats morethan 100 times perminute.
0956-0969 C36S3 BDOL-829900 8/5/04 4:36 AM Page 960
and tea—is a CNS stimulant. Its effectsinclude increased alertness and somemood elevation. Caffeine also causes anincrease in heart rate and urine produc-tion, which can lead to dehydration.
Nicotine, a substance found intobacco, is also a stimulant. By in-creasing the release of the hormoneepinephrine, nicotine increases heartrate, blood pressure, breathing rate,and stomach acid secretion. Althoughnicotine is the addictive substance intobacco, there are many other harm-ful chemicals found in tobacco prod-ucts. Smoking cigarettes leads to anincreased risk of lung cancer and car-diovascular disease. Use of chewingtobacco is associated with oral andthroat cancers.
Depressants: Alcohol and barbiturates
As you already know, depressantsslow down the activities of the CNS.All CNS depressants relieve anxiety,but most produce noticeable sedation.
One of the most widely abuseddrugs in the world today is alcohol.Easily produced from various grainsand fruits, this depressant is distrib-uted throughout a person’s body viathe bloodstream. Like other drugs,alcohol affects cellular communica-tion by influencing the release of orinteracting with receptors for severalimportant neurotransmitters in thebrain. Alcohol also appears to blockthe movement of sodium and calciumions across the cell membrane, aprocess that is important in the trans-mission of impulses and the release ofneurotransmitters.
Tolerance to the effects of alcoholdevelops as a result of heavy alcoholconsumption. Addiction to alcohol—alcoholism—can cause the destruc-tion of nerve cells and brain dam-age. A number of organ diseases aredirectly attributable to chronic alco-hol use. For example, cirrhosis, a har-dening of the tissues of the liver, is acommon affliction of alcoholics.
36.3 THE EFFECTS OF DRUGS 961
Table 36.1 Commonly Abused Drugs
Category • Substance Commercial or Street Name Potential Health Hazards
Cannabinoid• Marijuana • Grass, joints, pot, reefer, weed Respiratory problems, impaired learning
Stimulants• Cocaine • Blow, coke, crack, rock Increased heart rate and blood pressure, • Methylphenidate • Ritalin, Skippy, vitamin R irregular heart beat, heart failure, and • Nicotine • Chew, cigarettes, cigars weight loss• Methamphetamine • Ice, speed, glass• MDMA • Ecstasy, Eve
Depressants• Benzodiazepines • Librium, Valium, Xanax, Respiratory depression and arrest, lowered
downers, sleeping pills blood pressure, poor concentration• Barbiturates • Barbs, red birds, yellows
Hallucinogens• LSD • Cubes, microdot Chronic mental disorders, nausea, flashbacks
Opioids• Heroin • H, junk, skag, smack Respiratory depression and arrest, collapsed veins
Other• Inhalants • Paint thinners, gasoline, Headache, nausea, vomiting, unconsciousness,
butane, nitrates, laughing gas sudden death• Anabolic steroids • Juice Liver and kidney cancer, acne, high blood pressure• Ketamine • Special K, vitamin K Respiratory depression and arrest, nausea, vomiting
0956-0969 C36S3 BDOL-829900 8/5/04 4:36 AM Page 961
Barbiturates (bar BIH chuh ruts) are sedatives and anti-anxiety drugs.When barbiturates are used in excess,the user’s respiratory and circulatorysystems become depressed. Chronicuse results in addiction.
Narcotics: Opiates
Most narcotics are opiates, derivedfrom the opium poppy. They actdirectly on the brain. The mostabused narcotic in the United Statesis heroin. It depresses the CNS, slowsbreathing, and lowers heart rate.Tolerance develops quickly, and with-drawal from heroin is painful.
Hallucinogens: Natural and synthetic
Natural hallucinogens have beenknown and used for thousands ofyears, but the abuse of hallucinogenicdrugs did not become widespread inthe United States until the 1960s,
when new synthetic versions becamewidely available.
Hallucinogens (huh LEW sun uhjunz) stimulate the CNS—alteringmoods, thoughts, and sensory percep-tions. The user sees, hears, feels,tastes, or smells things that are notactually there. This disorientation canimpair the user’s judgment and placehim or her in a potentially dangeroussituation. Hallucinogens also increaseheart rate, blood pressure, respira-tory rate, and body temperature, andsometimes cause sweating, saliva-tion, nausea, and vomiting. After largeenough doses, convulsions of thebody may even occur.
Unlike the hallucinogens shown inFigure 36.20, LSD—or acid—is asynthetic drug. The mechanism bywhich LSD produces hallucinations isstill debated, but it may involve theblocking of a CNS neurotransmitter.
Describe the effectsof hallucinogens on the body.
(l)Matt Meadows/Peter Arnold, Inc., (r)Holt Studios International/Photo Researchers
Ergot, a mold disease of cerealgrains, contains a hallucinogenchemically related to LSD.
B
Mushrooms of the genus Psilocybe con-tain the CNS hallucinogen psilocybin.These mushrooms are considered sacredby certain Native American tribes, whouse them in traditional religious rites.
A
Figure 36.20Some hallucinogensare found in nature.
962 THE NERVOUS SYSTEM
0956-0969 C36S3 BDOL-829900 8/5/04 4:37 AM Page 962
Anabolic steroidsAnabolic steroids are synthetic
drugs that are similar to the hormonetestosterone. Like testosterone, ana-bolic steroids stimulate muscles toincrease in size. Physicians use ana-bolic steroids in the treatment of hor-mone imbalances or diseases thatresult in a loss of muscle mass. Abuseof anabolic steroids is associated withinfertility in men, high cholesterol,and extreme mood swings.
Breaking the HabitOnce a person has become addicted
to a drug, breaking the habit can bevery difficult. Recall that an addictioncan involve both physiological and psy-chological dependencies. Besides thedesire to break the addiction, studieshave shown that people usually needboth medical and psychological ther-apy—such as counseling—to be suc-cessful in their treatment. Supportgroups such as Alcoholics Anonymousallow addicts to share their experiencesin an effort to maintain sobriety. Often,people going through the same recov-ery are able to offer the best support.
Nicotine replacement therapyNicotine replacement therapy is one
example of a relatively successful drugtreatment approach. People who are
trying to break their addiction totobacco often go through stressfulwithdrawals when they stop smokingcigarettes. To ease the intensity of the withdrawal symptoms, patientswear adhesive patches that slowlyrelease small amounts of nicotine into their bloodstream, as shown inFigure 36.21. Alternatively, pieces ofnicotine-containing gum are chewedperiodically to temporarily relievecravings.
Understanding Main Ideas1. How can drugs affect levels of neurotransmitters
between neurons?
2. In what ways can drugs be used to treat a cardiovascular problem?
3. Identify the different classes of drugs. Give an example of each class.
4. How does nicotine affect the body?
Thinking Critically5. Form a hypothesis as to how a person develops
tolerance to a drug.
6. Compare and Contrast Distinguish betweenstimulants and depressants, comparing theireffects on the body. For more help, refer toCompare and Contrast in the Skill Handbook.
SKILL REVIEWSKILL REVIEW
36.3 THE EFFECTS OF DRUGS 963Laura Sifferlin
Figure 36.21To help break an addiction to tobacco, this patient iswearing a patch on his arm that releases small amountsof nicotine directly into his bloodstream.
ca.bdol.glencoe.com/self_check_quiz
0956-0969 C36S3 BDOL-829900 8/5/04 4:38 AM Page 963
Before YouBegin
Depending on their chemi-cal composition, drugsaffect different parts ofyour body. Stimulants anddepressants are drugs thataffect the central nervoussystem and the autonomicnervous system. Stimulantsincrease the activity of thesympathetic nervous sys-tem and cause an increasein your breathing rate and in your heart rate.Depressants decrease theactivity of the sympatheticnervous system, reducingyour breathing and heartrates. In this lab, you willinvestigate the effects thatdifferent drugs have on anorganism’s heart rate.
964 THE NERVOUS SYSTEM
What drugs affect theheart rate of Daphnia?
ProblemWhat legally available drugs are stimulants to the heart?What legal drugs are depressants? Because these drugs arelegally available, are they less dangerous?
HypothesesBased on what you learned in this chapter, which of the drugslisted under Possible Materials do you think are stimulants?Which are depressants? How will they affect the heart rate in Daphnia? Make a hypothesis concerning how each of thedrugs listed will affect heart rate.
ObjectivesIn this BioLab, you will:■ Measure the resting heart rate in Daphnia.■ Compare the resting heart rate with the heart rate when a
drug is applied.
Possible Materialsaged tap water dropperDaphnia culture microscopedilute solutions of coffee, tea, microscope slide
cola, ethyl alcohol, tobacco, and cough medicine (containing dextromethorphan)
Safety PrecautionsCAUTION: Do not drink any of the solutions used in this lab.Always wear goggles in the lab. Use caution when workingwith a microscope, microscope slides, and glassware.
Skill HandbookIf you need help with this lab, refer to the Skill Handbook.
PREPARATIONPREPARATION
Matt Meadows
0956-0969 C36S3 BDOL-829900 8/5/04 4:39 AM Page 964
36.3 THE EFFECTS OF DRUGS 965
Color-enhanced SEMMagnification: 1200�Daphnia
1. Design an experiment to measure the effect on heart rate of four of the drug-containing sub-stances in the Possible Materials list.
2. Design and construct a data table for recording your data.
Check the Plan1. Be sure to consider what you will use as a control.2. Plan to add two drops of a drug-containing sub-
stance directly to the slide.3. When you are finished testing one drug, you will
need to flush the used Daphnia with the solution into a beaker of aged tap water provided by your teacher. Plan to use a new Daphnia for each sub-stance tested.
4. Make sure your teacher has approved your experimental plan before you proceed further.
5. Begin your experiment by using a dropper to place a single Daphnia on a slide. Observe the animal on low power and find its heart. CAUTION: Wash your hands with soap and water immediately after makingobservations.
6. Collect the used Daphnia in abeaker of aged tap water and give them to your teacher.Make wise choices about the disposal or recycling of othermaterials.
CLEANUP AND DISPOSAL
PLAN THE EXPERIMENTPLAN THE EXPERIMENT
ANALYZE AND CONCLUDEANALYZE AND CONCLUDE
1. Infer Examine your results and infer which drugs are stimulants. Which are depressants?
2. Check Your Hypotheses Compare yourpredicted results with the experimental data.Explain whether or not your data supportyour hypotheses regarding the drugs’ effects.
3. Draw Conclusions How do the drugs affectthe heart rate of this animal?
4. Compare your data to thatof other groups. How can you account fordifferences in results with other lab groups?How would you alter your experiment if youdid it again?
ERROR ANALYSIS
Use Variables, Constants, and ControlsMany other over-the-counter drugs are avail-able. You may wish to test their effect on theheart rate of Daphnia.
Web Links To find out more about drug effects, visit
Sinclair Stammers/Photo Researchers
ca.bdol.glencoe.com/drug_effects
0956-0969 C36S3 BDOL-829900 8/5/04 4:44 AM Page 965
966 THE NERVOUS SYSTEM
Scanning the Mind
Advancements in medical technology have led to instruments—such as X-ray and
magnetic resonance imaging (MRI) machines—that can examine the human body in a noninva-sive way. In addition to X rays and MRIs,another technology has been added to the med-ical toolbox—positron emission tomography(PET). This instrument is unique in that itallows a physician to view internal body tissueswhile they carry out their normal daily functions.
PET scanners are excellent tools for study-ing the human brain. By monitoring either theblood flow to an area or the amount of glucosebeing metabolized there, doctors are able topinpoint active sections of the brain.
Here’s how it works: The patient is injected with a compound containing radioactive iso-topes. These isotopes emit detectable radiationand can be tracked by the sensitive PET scan-ner. Computers create a picture of brain activ-ity by converting the energy emitted from theradioisotopes into a colorful map. The imageindicates the location of an activity, such asglucose utilization, and its relative intensity invarious regions.
Valuable research PET scanners are impor-tant in brain research, including the detectionand diagnosis of brain tumors, the evaluation ofdamage due to stroke, and the mapping of brainfunctions. PET scans can also be used to seehow learning takes place in the brain. Theimages on this page show activity in the left andright brains of two people. Each person wasgiven a list of nouns and asked to visualize them.The unpracticed brain (top) had no previousexperience with this exercise and thus was forcedto engage in a high level of brain activity to per-form the task. The practiced brain (bottom), bycomparison, was able to picture the words withmuch less brain activity. Biologists can discoverfunctions of different parts of the brain and theirroles in learning.
PET scans are also proving useful in the study ofdrug and alcohol addiction. Addicts can be giventhe addictive drug and then asked questionsabout their physical and emotional status whilethe scanner records metabolic activity in thebrain. Researchers hope that information gainedabout how the brain works from the study ofdrug addiction will provide help in diagnosingand treating other illnesses such as manic-depressive psychosis and schizophrenia.
Evaluate Evaluate the impact of research done on the brain through PET scans. What effect hasthis had on scientific thought and society? Whatnew information about the brain has been discov-ered through studies using a PET scan? How willthis affect future diagnosis and treatment of braindiseases or disorders?
To find out more about PET scans, visit
PET scans
Wellcome Dept. of Cognitive Neurology/Science Photo Library/Custom Medical Stock Photo
ca.bdol.glencoe.com/biotechnology
0956-0969 C36S3 BDOL-829900 8/5/04 4:46 AM Page 966
Section 36.1
Key Concepts■ The senses of taste and smell are responses
to chemical stimulation.■ The sense of sight is a response to light
stimulation.■ The senses of hearing, balance, and touch
are responses to mechanical stimulation.
Vocabularycochlea (p. 954)cones (p. 952)retina (p. 952)rods (p. 952)semicircular canals
(p. 954)taste bud (p. 952)
Key Concepts■ Drugs act on the body’s nervous system.■ Some medicinal uses of drugs include
relieving pain and treating cardiovascularproblems and nervous disorders.
■ The misuse of drugs involves taking amedicine for an unintended use. Drugabuse involves using a drug for a non-medical purpose.
Vocabularyaddiction (p. 959)depressant (p. 958)drug (p. 956)hallucinogen (p. 962)narcotic (p. 957)stimulant (p. 958)tolerance (p. 959)withdrawal (p. 959)
The Senses
STUDY GUIDESTUDY GUIDE
CHAPTER 36 ASSESSMENT 967
Section 36.3
Section 36.2
Vocabularyautonomic nervous
system (p. 949)axon (p. 943)central nervous system
(p. 946)cerebellum (p. 947)cerebrum (p. 947)dendrite (p. 943)medulla oblongata
(p. 947)neuron (p. 943)neurotransmitter (p. 946)parasympathetic nervous
system (p. 949)peripheral nervous
system (p. 947)reflex (p. 948)somatic nervous system
(p. 948)sympathetic nervous
system (p. 949)synapse (p. 946)
The NervousSystem
The Effects of Drugs
To help you review thesenses, use the Organizational StudyFold on page 951.
Key Concepts■ The neuron is the basic structural unit of
the nervous system. Impulses move along aneuron in a wave of changing charges.
■ The central nervous system consists of thebrain and spinal cord.
■ The peripheral nervous system relays messages to and from the central nervoussystem. It consists of the somatic and autonomic nervous systems.
Matt Meadows
ca.bdol.glencoe.com/vocabulary_puzzlemaker
0956-0969 C36S3 BDOL-829900 8/5/04 4:47 AM Page 967
Cochlea
Ovalwindow
Semicircularcanals
Stapes
Cerebrum
PonsMedullaoblongata
Cerebellum
968 CHAPTER 36 ASSESSMENT
Review the Chapter 36 vocabulary words listed inthe Study Guide on page 967. For each set ofvocabulary words, choose the one that does notbelong. Explain why it does not belong.
1. axon—cochlea—dendrite2. rods—cones—reflex3. retina—depressant—stimulant4. synapse—taste bud—neurotransmitter5. tolerance—addiction—cerebrum6. neuron—drug—hallucinogen
7. Which of the following is NOT a type ofneuron?A. interneuronB. sensory neuronC. motor neuronD. stimulus neuron
8. Which portion of the brain controls balance,posture, and coordination?A. ponsB. medulla oblongataC. cerebellumD. cerebrum
9. Which part of the ear is involved in main-taining balance?A. semicircular canalsB. oval windowC. stapesD. cochlea
10. Which type of neuron carries impulsestoward the brain?A. sensory C. associationB. motor D. none of the above
11. Complete the concept map by using the fol-lowing vocabulary terms: neurons, neuro-transmitters, axons, dendrites, synapses.
12. Open Ended Compare and contrast thesomatic nervous system and the autonomicnervous system.
13. Open Ended Identify how the nervous systemresponds to external stimuli.
14. Open Ended The drug ephedrine is a sympa-thetic nervous system mimic drug. Whatcould be the effects of this drug on the body?
15. Visit to answer the follow-
ing questions. What is a spinal cord injury?What treatments are available? Whatresearch is currently being done to helppeople overcome the effects of a spinal cord injury?
16. Infer Local anesthetics block the opening ofsodium channels in nerve cells. Explain howthis would affect the transmission of painimpulses.
REAL WORLD BIOCHALLENGE
3.2.
contain branchlikeextensions called
contain long, singleextensions called
release chemicalscalled
4.
5.
1.
which diffuseacross
ca.bdol.glencoe.com/chapter_test
ca.bdol.glencoe.com
0956-0969 C36S3 BDOL-829900 8/5/04 4:48 AM Page 968
17. Recognize Cause and Effect During arough ferry crossing, the horizon seems tobe moving up and down as you hold on tothe railing. You begin to feel seasick. Explainwhat is happening in your body that mightbe causing you to feel this sensation.
18. Hypothesize Patients with multiple sclerosislose the ability to control their movement.This is due to a continual loss of myelinsheaths on motor neurons. Form a hypothesisas to how this would cause these patients tolose control of their ability to move.
CHAPTER 36 ASSESSMENT 969
Constructed Response/Grid InRecord your answers on your answer document.
25. Open Ended Neuron B is hyperpolarized, that is, it is more difficult for the threshold to bereached. Explain how this condition would affect the transmission of nerve impulses in thisneuron. Form a hypothesis about how the neuron became hyperpolarized.
26. Open Ended Exposure to loud noises, such as a jet engine, damages the hair cells in thecochlea. Explain why extended exposure to loud noise results in hearing loss.
Multiple ChoiceUse the diagram to answer questions 19–21.
19. The diagram above shows four possibleblockages of nerve impulses at A, B, C, and Dby an anesthetic. If the patient can move herhand but can’t feel it, where is the blockage?A. A C. CB. B D. D
20. If the patient can feel a pinprick but cannotmove her hand, where is the blockage?A. A C. CB. B D. D
21. If the patient cannot feel a pinprick or moveher hand, where is the blockage?A. A C. CB. B D. D
Study the graph and answer questions 22–25.
22. What is the membrane potential of NeuronA when it is polarized?A. �80 mV C. �55 mVB. �70 mV D. �30 mV
23. What is the membrane potential of NeuronB when it is polarized?A. �80 mV C. �55 mVB. �70 mV D. �30 mV
24. What is the highest membrane potentialreached by Neuron A while it is depolarized?A. �80 mV C. �55 mVB. �70 mV D. �30 mV
Brain
Spinal cord
Sensoryneuron
Motor neuron
A
B
C D
Mem
bra
ne
po
ten
tial
(m
illiv
olt
s, m
V)
Time (milliseconds, ms)
–80–70
–55
0
+30
Polarized
Membrane Potential of Neurons
DepolarizedRepolarized
Stimulus
Threshold
Neuron ANeuron B
ca.bdol.glencoe.com/standardized_test
9d
9d
9d
The assessed California standard appears next to the question.
0956-0969 C36S3 BDOL-829900 8/5/04 4:49 AM Page 969
