35–3 Divisions Of The Nervous System Section 35–3
0890 0914 bi c07 te3/13/062:28 PMPage 90135–3 Divisions of the Nervous SystemSection 35–31 FOCUSObjectivesNeurons do not act alone. Instead, they are joined together toform a complex network—the nervous system. The humannervous system is separated into two major divisions: thecentral nervous system and the peripheral nervous system.The central nervous system is the control center of the body.The functions of the central nervous system are similar to thoseof the central processing unit of a computer.The centralnervous system relays messages, processes information,and analyzes information. The peripheral nervous systemreceives information from the environment and relays commands from the central nervous system to organs and glands.The Central Nervous SystemKey ConceptsCAa What are the functions of thecentral nervous system? What are the functions of the twodivisions of the peripheralnervous system?Vocabularya BI 9.bmeninges cerebrospinal fluidcerebrum cerebellumbrain stem thalamushypothalamus reflexreflex arcReading Strategy:Asking Questions Before youThe central nervous system consists of the brain, shown inFigure 35–9, and the spinal cord. The skull and vertebrae in thespinal column protect the brain and spinal cord. Both the brainand spinal cord are wrapped in three layers of connective tissueknown as meninges (muh-NIN-jeez). Between the meningesand the central nervous system tissue is a space filled withcerebrospinal (sehr-uh-broh-SPY-nul) fluid. Cerebrospinal fluidbathes the brain and spinal cord and acts as a shock absorberthat protects the central nervous system. The fluid also allowsfor the exchange of nutrients and waste products between bloodand nervous tissue.read, rewrite the headings in thesection as how, why, or whatquestions about the nervoussystem. As you read, write downthe answers to your erebellumPonsBrain stemMedulla oblongataVocabulary PreviewPoint out that all of the Vocabularyterms refer to structures within thebrain except for two terms. Ask:Which two terms do not refer tostructures in the brain? (Reflex andreflex arc) Challenge students to predict what these two terms mightmean, and then have them check tosee if they were correct as they readthe section.Reading Strategy왔 Figure 35– 9The brain helps to relay messages,process information, and analyze information. The brainconsists of the cerebrum, cerebellum, and brain stem.Pituitary gland35.3.1 Identify the functions of thecentral nervous system.35.3.2 Describe the functions of thetwo divisions of the peripheral nervous system.Spinal cordPossible questions students mightwrite include: What are the parts ofthe central nervous system? (Thebrain and the spinal cord) What is therole of the brain? (It is the mainswitching unit of the central nervoussystem.) What is the function of thespinal cord? (It is the main communications link between the brain and therest of the body.) What structuresmake up the peripheral nervous system? (All the nerves and associatedcells that are not part of the brain andthe spinal cord)2 INSTRUCTThe Central NervousSystemUse VisualsSECTION RESOURCESPrint:Timr Laboratory Manual A, Chapter 35 Lab Laboratory Manual B, Chapter 35 Labave Teaching Resources, Lesson Plan S35–3,eAdapted Section Summary 35–3, AdaptedWorksheets 35–3, Section Summary 35–3,Worksheets 35–3, Section Review 35–3 Reading and Study Workbook A,Section 35–3 Adapted Reading and Study Workbook B,Section 35–3 Issues and Decision Making, Issues andDecisions 44Technology: iText, Section 35–3 Transparencies Plus, Section 35–3Figure 35–9 Point out the locationof the cerebrum and cerebellum.Explain that the brain stem is theregion in front of the cerebellumthat contains the pons and medullaoblongata. Ask: Which part of thehuman brain is the largest part?(Cerebrum) Where in the brain arestructures with endocrine functionlocated? (Above the brain stem)Nervous System901
0890 0914 bi c07 te3/10/067:40 PMPage 902The Brain35–3 (continued)The brain is the place to which impulses flow and from whichimpulses originate. The brain contains approximately 100billion neurons, many of which are interneurons. The brain hasa mass of about 1.4 kilograms.The BrainBuild Science SkillsCalculating Help students appreciate how the folds in the brain greatlyincrease its surface area. First, havestudents measure the sides of a smallbox, such as a cereal box or shoebox, and use the measurements tocalculate its surface area. Next, havestudents stuff the box with foldedsheets of newspaper until the box isfull. Then, have students count thenumber of sheets of newspaper andfind their total area (by multiplyingthe number of sheets by the area ofone sheet). Students should add thisnumber to the surface area of thebox. Ask: How much was the surface area increased by the foldedsheets? (Exact answers will vary.Students will find that the surface areawas increased greatly by the additionof the folded sheets.)The Cerebrum The largest and most prominent region of theFrontal lobeParietal lobeTemporal lobeOccipital lobe왖 Figure 35–10 This view of thecerebrum shows the four differentlobes of the brain. Different functions of the body are controlled bydifferent lobes of the brain.Drawing Conclusions The frontallobe controls voluntary musclemovements. What might happen if thispart of the brain became injured?Use Community ResourcesInvite a diagnostic imaging technician to visit the class and explain howbrain injuries, tumors, and otherabnormalities of the brain are diagnosed. Ask the visitor to describeMRIs and CT scans and what theyreveal about the brain. If possible,have the visitor bring sample imagesor scans to share with students. Urgestudents to take notes during the talkand later use the notes to write asummary of what they learned.The Cerebellum The second largest region of the brain is thecerebellum. The cerebellum is located at the back of the skull.Although the commands to move muscles come from the cerebralcortex, the cerebellum coordinates and balances the actions ofthe muscles so that the body can move gracefully and efficiently.The Brain Stem The brain stem connects the brain andN S TANS TADownload a worksheeton the human brain for students tocomplete, and find additionalteacher support from NSTASciLinks.human brain is the cerebrum. The cerebrum is responsible forthe voluntary, or conscious, activities of the body. It is the site ofintelligence, learning, and judgment. A deep groove divides thecerebrum into right and left hemispheres. The hemispheres areconnected by a band of tissue called the corpus callosum.Folds and grooves on the surface of each hemisphere greatlyincrease the surface area of the cerebrum. Each hemisphere ofthe cerebrum is divided into regions called lobes. The lobes arenamed for the skull bones that cover them. The locations of fourlobes of the brain are shown in Figure 35–10.Remarkably, each half of the cerebrum deals mainly withthe opposite side of the body. Sensations from the left side of thebody go to the right hemisphere of the cerebrum, and those fromthe right side of the body go to the left hemisphere. Commandsto move muscles are generated in the same way. The left hemisphere controls the body’s right side, and the right hemispherecontrols the body’s left side. Some studies have suggested thatthe right hemisphere may be associated with creativity andartistic ability, whereas the left hemisphere may be associatedwith analytical and mathematical ability.The cerebrum consists of two layers. The outer layer of thecerebrum is called the cerebral cortex and consists of graymatter. Gray matter consists mainly of densely packed nervecell bodies. The cerebral cortex processes information from thesense organs and controls body movements. The inner layer ofthe cerebrum consists of white matter, which is made up ofbundles of axons with myelin sheaths. The myelin sheaths givethe white matter its characteristic color. White matter connectsthe cerebral cortex and the brain stem.For: Links on thehuman brainVisit: www.SciLinks.orgWeb Code: cbn-0353spinal cord. Located just below the cerebellum, the brain stemincludes two regions known as the pons and the medulla oblongata. Each of these regions regulates the flow of informationbetween the brain and the rest of the body. Some of the body’smost important functions—including blood pressure, heart rate,breathing, and swallowing—are controlled in the brain stem.UNIVERSAL ACCESSInclusion/Special NeedsUse a hands-on experience to help studentsunderstand the functions of the somatic andautonomic nervous systems. First, have studentsraise one hand over their heads. Tell them thatthis behavior is voluntary and controlled by thesomatic nervous system. Then, have them feeltheir pulse to detect their heartbeat. Explain thatthe beating of their heart is involuntary and controlled by the autonomic nervous system.902Chapter 35Less Proficient ReadersThe organization of the peripheral nervous system may be confusing to less proficient readers.Have them create a concept map to show how itis subdivided, including the sensory and motordivisions, somatic and autonomic nervous systems, and sympathetic and parasympatheticnervous systems. After they have completed theirconcept maps, call on students to name the function of each subdivision.
0890 0914 bi c07 te3/10/067:40 PMPage 903The Thalamus and Hypothalamus The thalamus andhypothalamus are found between the brain stem and the cerebrum. The thalamus receives messages from all of the sensoryreceptors throughout the body and then relays the informationto the proper region of the cerebrum for further processing. Justbelow the thalamus is the hypothalamus. The hypothalamusis the control center for recognition and analysis of hunger, thirst,fatigue, anger, and body temperature. The hypothalamus alsocontrols the coordination of the nervous and endocrine systems.You will learn more about the endocrine system in a later chapter.The Spinal CordLike a major telephone line that carries thousands of calls atonce, the spinal cord is the main communications link betweenthe brain and the rest of the body. Thirty-one pairs of spinalnerves branch out from the spinal cord, connecting the brain toall of the different parts of the body. Certain kinds of information, including some kinds of reflexes, are processed directly inthe spinal cord.A reflex is a quick, automatic response to a stimulus.Sneezing and blinking are two examples of reflexes. A reflexallows your body to respond to danger immediately, withoutspending time thinking about a response. Animals rely heavilyon reflex behaviors for survival.What is a reflex?The Peripheral Nervous SystemThe peripheral nervous system lies outside of the central nervous system. It consists of all of the nerves and associated cellsthat are not part of the brain and the spinal cord. Included hereare cranial nerves that pass through openings in the skull andstimulate regions of the head and neck, spinal nerves, andganglia. Ganglia are collections of nerve cell bodies.The peripheral nervous system can be divided into thesensory division and the motor division.The sensorydivision of the peripheral nervous system transmitsimpulses from sense organs to the central nervous system. The motor division transmits impulses from thecentral nervous system to the muscles or glands. Themotor division is further divided into the somatic nervoussystem and the autonomic nervous system.The Spinal CordHow do you respondto an externalstimulus?Materials sheet of scrap paperProcedure1. Have your partner put on safetygoggles.2. Crumple up a sheet of scrappaper into a ball.3. Watch your partner’s eyescarefully as you toss the paperball toward his or her face.Record your partner’s reaction.4. Repeat step 3, three more times.5. Exchange roles and repeat steps1, 3, and 4.Analyze and Conclude1. Observing What reaction didyou observe when you tossedthe ball at your partner’s face?2. Observing Was that reactionvoluntary? What kind of reaction is this?3. Comparing and ContrastingDid you see any change inbehavior as you repeatedstep 3? If so, how would youdescribe this change?4. Inferring What is the functionof the blink reflex?Objective Students will be able todescribe a common reflex andexplain its function.Skills Focus Observing,InferringMaterials Sheet of scrap paperTime 10 minutesSafety Make sure students put ontheir safety goggles before thepaper ball is thrown at them.Expected Outcome Students whohave the ball thrown at them shouldautomatically blink.Analyze and Conclude1. The partner blinked when thepaper ball was thrown at him orher.2. The reaction happened involuntarily. Therefore, it is an automaticresponse, or reflex.3. After several repetitions, the partner may not blink because he or sheexpects the stimulus and is able tocontrol the response.4. The function of the blink reflex isto help protect the eyes from injury.DemonstrationBI 9.eWith the help of a student volunteer,demonstrate the knee-jerk reflex. Askstudents to observe how quickly thereflex occurs. Explain that this isbecause it is processed directly in thespinal cord and not in the brain.The Somatic Nervous System The somatic nervoussystem regulates activities that are under conscious control,such as the movement of the skeletal muscles. Every timeyou lift your finger or wiggle your toes, you are using themotor neurons of the somatic nervous system. Some somaticnerves are also involved with reflexes and can act with orwithout conscious control.HISTORY OF SCIENCEBroca’s areaIn the middle of the nineteenth century, PaulBroca, a French neurologist, discovered that asmall region just above the sylvian fissure of theleft frontal lobe of the cerebral cortex controls theability to speak words correctly (rather thansounds). This area is now called Broca’s area.Broca made his discovery by studying people withbrain damage who had lost the ability to speak.He also studied split-brain patients—peoplewhose hemispheres were no longer physicallyconnected due to brain damage. Broca’s discovery of this speech area was important for tworeasons. It provided some of the first evidencethat the left and right hemispheres of the brainhave separate functions, and it was one of the firstindicators that particular brain functions are localized in specific regions of the brain.The PeripheralNervous SystemBuild Science SkillsApplying Concepts Challenge students to explain how a person with ahealthy peripheral nervous systemcould lack nervous control of the legmuscles due to a spinal cord injury.Answers to . . .A quick, automaticresponse to a stimulus that is processedin the spinal cordFigure 35–10 There might be lesscontrol over voluntary muscle movements, such as walking and writing.Nervous System903
0890 0914 bi c07 te3/10/067:40 PMPage 90435–3 (continued)Objective Students will be able toconclude that a stronger stimulusdoes not produce a stronger nerveimpulse.Skills Focus DrawingConclusions, Evaluating,Applying ConceptsMaterials string, packing tape,scissors, 30-cm ruler, 3 plasticmousetrapsTime 20 minutesSafety Show students how to holdthe traps open safely with one handwhile using the other hand to inserta string through the bait platform.Strategy If students are workingwith a partner or in groups, makesure each student has a chance toset off the trap in step 3 in order toappreciate the all-or-nothing natureof the “reflex” response.Expected Outcome Studentsshould find that only a tug greaterthan a certain threshold triggers themousetraps.Analyze and Conclude1. A sufficiently strong tug is required.This level of force can be comparedwith the threshold level of stimulusrequired to activate a neuron.2. A stronger stimulus does not produce a stronger impulse because theresponse of a neuron is an all-ornothing response.3. Answers will vary. Students maysay the procedure is not an adequate model because it is slowerthan an actual reflex arc or becauseit uses mechanical instead of electrical impulses.4. Students should say that theyhandled the scissors carefully anddid not let the mousetrap snap ontheir ordEffector(responding muscle)Sensoryreceptors왖 Figure 35–11The peripheral nervoussystem transmits impulses from sense organs tothe central nervous system and back to musclesor glands. When you step on a tack, sensoryreceptors stimulate a sensory neuron, which relaysthe signal to an interneuron within the spinal cord.The signal is then sent to a motor neuron, which inturn stimulates a muscle in your leg to lift your leg.Chapter 35The Autonomic Nervous System Theautonomic nervous system regulates activitiesthat are automatic, or involuntary. The nerves ofthe autonomic nervous system control functions ofthe body that are not under conscious control. Theinfluence exerted on other body systems by theautonomic nervous system is a good example of aninterrelationship that is needed between systemsfor the body’s well-being. For instance, when youare running, the autonomic nervous system speedsup your heart rate and the blood flow to theskeletal muscles, stimulates the sweat glands andadrenal glands, and slows down the contractionsof the smooth muscles in the digestive system.The autonomic nervous system is furthersubdivided into two parts—the sympatheticnervous system and the parasympathetic nervoussystem. Most organs controlled by the autonomicnervous system are under the control of bothsympathetic and parasympathetic neurons.The sympathetic and parasympathetic nervoussystems have opposite effects on the same organsystem. The opposing effects of the two systems helpthe body maintain homeostasis. For example, heartrate is increased by the sympathetic nervous systembut decreased by the parasympathetic nervoussystem. The process of regulating heart rate can becompared to the process of controlling the speed of acar. One system is like the gas pedal and the other islike the brake. Because there are two different sets ofneurons, the autonomic nervous system can quicklyspeed up the activities of major organs in response toa stimulus or slam on the brakes if necessary.TEACHER TO TEACHERIn order to test reaction time, I divide the classinto pairs of students. One student should resthis or her elbow on a table and extend his or herarm over the side of the table. The second student should hold a meter stick in the air andrelease it unexpectedly. The first student shouldtry to catch the meter stick between the thumband index finger. Use the equation: time ( distance)/(9.8 m/s2 ). After each person hascalculated his or her reaction time, have students904If you accidentally step on a tack with your barefoot, your leg may recoil before you are aware of thepain. This rapid response (a reflex) is possiblebecause receptors in your skin stimulate sensoryneurons, which carry the impulse to your spinalcord. Even before the information is relayed to yourbrain, a group of neurons in your spinal cord automatically activates the appropriate motor neurons.These motor neurons cause the muscles in your legto contract, pulling your foot away from the tack.The pathway that an impulse travels from yourfoot back to your leg is known as a reflex arc. Asshown in Figure 35–11, a reflex arc includes asensory receptor (in this case, a receptor in your toe),sensory neuron, motor neuron, and effector (legmuscle). Some reflex arcs include interneurons. Inother reflex arcs, a sensory neuron communicatesdirectly with a motor neuron.record their times in a chart on the chalkboard tosee who has the best reaction time in the class.Using the meter stick and a physics equationallows the students to see the relationshipbetween physics and biology.—Charlotte ParnellBiology TeacherLakeside High SchoolHot Springs, AR
0890 0914 bi c07 te3/10/067:40 PMPage 905Build Science SkillsHow do reflexes occur?MousetrapMaterials string, scissors, 3 plasticmousetraps, packing tape, 30-cm rulerProcedure1. Using Models To model a synapse, cut a 30-cmpiece of string. CAUTION: Handle scissors carefully.2. Hold a mousetrap open. Pull the string through thebait platform as shown. CAUTION: Do not let themousetrap snap on your fingers. Slide a piece of tapeunder the bait platform and tape the trap to thetable as shown. Label the trap “sensory neuron.”3. Hold one end of the string in each hand. Gentlypull one end without setting off the trap. Nowgradually pull harder.4. To model a reflex arc, cut two more 30-cm piecesof string. Tie one end of each piece of string to thebait platform of a separate trap.5. Tape the 2 new traps to the table, 20 cm from thefirst trap. Label one new trap “motor neuron,” andthe other “brain.”6. Reset the first trap, and then set the new ones.Tape both ends of the strings attached to the newtraps to the top of the first trap. Leave these stringsslightly slack.TapeString7. Pull the strings attached to the bait platform of the“sensory neuron.”Analyze and Conclude1. Drawing Conclusions What was required forthe trap to close in step 3? How does this behaviorcompare to the transmission of a nerve impulse?2. Applying Concepts Does a stronger stimulusproduce a stronger nerve impulse? Explain youranswer.3. Evaluating Do you consider this procedure anadequate model of a reflex arc? Explain yourresponse by citing specific details. If not, proposean alternative model.4. SAFETY Explain how you demonstrated safepractices as you carried out this investigation.35–3 Section Assessment1.Key Concept Discuss theoverall function of the centralnervous system.2.Key Concept Describe thefunctions of the two divisions ofthe peripheral nervous system.3. How is the central nervoussystem protected from injury?4. What is the role of the hypothalamus?5. Is a reflex part of the centralnervous system, the peripheralnervous system, or both? Explain.6. Critical Thinking InferringWould you expect the cerebrumof a bird to be more or lessdeveloped relative to its size thanthe cerebrum of a human?Explain. (Hint: You may want toreview Section 33–3.)Structure and FunctionUsing Section 34–1, decidewhich parts of the nervoussystem are most likely to beinvolved with innate, orinborn, behaviors. Which partsare likely to be involved withlearned behaviors? Explainyour reasoning.Observing Demonstrate the pupillary reflex, which is the automaticwidening or narrowing of the pupilof the eye when the amount of lightfalling on it changes. Ask several volunteers to cover their eyes with ablindfold and keep their eyes closed.After a few minutes, have the volunteers uncover and open their eyeswhile the other students observewhat happens to the size of the volunteers’ pupils. Ask: How did thesize of their pupils change? (Theywere wide at first and gradually narrowed.) How long did the changetake? (Several seconds)3 ASSESSEvaluate UnderstandingAsk students to make a concept mapof the divisions and subdivisions ofthe nervous system.ReteachHave each student create a crossword puzzle using the Vocabularyterms. Then, have students exchangeand solve the puzzles.Reflex arcs are most likely to beinvolved with innate behaviors,which are functional the first timethey are performed. The brainplays a major role in learnedbehaviors, which depend on datacollected through experiencebeing processed and analyzed.If your class subscribes to the iText,use it to review the Key Concepts inSection 35–3.35 –3 Section Assessment1. To relay messages and to process and analyzeinformation2. The sensory division transmits impulsesfrom sense organs to the central nervoussystem. The motor division transmitsimpulses from the central nervous systemto muscles.3. It is protected by the skull and vertebrae, themeninges, and the cerebrospinal fluid.4. It recognizes and analyzes hunger, thirst,fatigue, anger, and body temperature. It alsocontrols the coordination of the nervous andendocrine systems.5. Both, because it involves sensory and motorneurons of the peripheral system and isprocessed in the spinal cord6. Less developed, because birds have less abilityto think and learn than humans doNervous System905
nervous system is separated into two major divisions: the central nervous system and the peripheral nervous system. The central nervous system is the control center of the body. The functions of the central nervous system are similar to those of the central processing unit of a computer. The central nervous system relays messages, processes .
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