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Chapter 48Neurons, Synapses, and SignalingCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsPowerPoint Lecture Presentations for Biology Eighth EditionNeil Campbell and Jane ReeceLectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings1

Fig. 48-12Figure 48.1 What makes this snail such a deadly predator?For the Discovery Video Novelty Gene, go to Animation and Video Files.

Sensors detect external stimuli and internal conditions and transmit information along sensory neuronsSensory information is sent to the brain or ganglia, where interneurons integrate the informationMotor output leaves the brain or ganglia via motor neurons, which trigger muscle or gland activity

Concept 48.1: Neuron organization and structure reflect function in information transferCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings3Many animals have a complex nervous system which consists of:A central nervous system (CNS) where integration takes place; this includes the brain and a nerve cordA peripheral nervous system (PNS), which brings information into and out of the CNS Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings4

Fig. 48-3SensorSensory inputIntegrationEffectorMotor outputPeripheral nervoussystem (PNS)Central nervoussystem (CNS)5Figure 48.3 Summary of information processing

Fig. 48-4DendritesStimulusNucleusCellbodyAxonhillockPresynapticcellAxonSynaptic terminalsSynapsePostsynaptic cellNeurotransmitterNeuron Structure and Function6Figure 48.4 Neuron structure and organizationFor the Cell Biology Video Dendrites of a Neuron, go to Animation and Video Files.

Fig. 48-6OUTSIDECELL [K+]5 mM [Na+]150 mM [Cl]120 mMINSIDECELL [K+]140 mM [Na+]15 mM [Cl]10 mM [A]100 mM(a)(b)OUTSIDECELLNa+KeyK+Sodium-potassiumpumpPotassiumchannelSodiumchannelINSIDECELLConcept 48.2: Ion pumps and ion channels maintain the resting potential of a neuronIn a resting neuron, the currents of K+ and Na+ are equal and opposite, and the resting potential across the membrane remains steady7Figure 48.6 The basis of the membrane potentialConcept 48.3: Action potentials are the signals conducted by axonsNeurons contain gated ion channels that open or close in response to stimuli

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Fig. 48-8TECHNIQUEMicroelectrodeVoltagerecorderReferenceelectrode9Figure 48.8 Intracellular recording

Fig. 48-9Stimuli+50+50Stimuli00Membrane potential (mV)Membrane potential (mV)5050ThresholdThresholdRestingpotentialRestingpotentialHyperpolarizations100100012345Time (msec)(a) Graded hyperpolarizationsTime (msec)(b) Graded depolarizationsDepolarizations012345Strong depolarizing stimulus+500Membrane potential (mV)50ThresholdRestingpotential100Time (msec)0123456(c) Action potentialActionpotential10Figure 48.9 Graded potentials and an action potential in a neuronProduction of Action PotentialsVoltage-gated Na+ and K+ channels respond to a change in membrane potentialWhen a stimulus depolarizes the membrane, Na+ channels open, allowing Na+ to diffuse into the cellThe movement of Na+ into the cell increases the depolarization and causes even more Na+ channels to openA strong stimulus results in a massive change in membrane voltage called an action potentialCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings11

Fig. 48-9cStrong depolarizing stimulus+50Membrane potential (mV)50ThresholdRestingpotential1000234Time (msec)(c) Action potential150Actionpotential612Figure 48.9c Graded potentials and an action potential in a neuronGeneration of Action Potentials: A Closer LookA neuron can produce hundreds of action potentials per secondThe frequency of action potentials can reflect the strength of a stimulusAn action potential can be broken down into a series of stages

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Fig. 48-10-5KeyNa+K++50ActionpotentialThreshold0145150Resting potentialMembrane potential(mV)100TimeExtracellular fluidPlasmamembraneCytosolInactivation loopResting stateSodiumchannelPotassiumchannelDepolarizationRising phase of the action potentialFalling phase of the action potential5Undershoot23213414Figure 48.10 The role of voltage-gated ion channels in the generation of an action potential

Fig. 48-11-3AxonPlasmamembraneCytosolActionpotentialNa+ActionpotentialNa+K+K+ActionpotentialK+K+Na+15Figure 48.11 Conduction of an action potentialConduction SpeedThe speed of an action potential increases with the axons diameterIn vertebrates, axons are insulated by a myelin sheath, which causes an action potentials speed to increaseMyelin sheaths are made by glia oligodendrocytes in the CNS and Schwann cells in the PNSCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings16

Fig. 48-12AxonSchwanncellMyelin sheathNodes ofRanvierNode of RanvierSchwanncellNucleus ofSchwann cellLayers of myelinAxon0.1 m17Figure 48.12 Schwann cells and the myelin sheathConcept 48.4: Neurons communicate with other cells at synapsesAt electrical synapses, the electrical current flows from one neuron to anotherAt chemical synapses, a chemical neurotransmitter carries information across the gap junctionMost synapses are chemical synapsesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings18

Fig. 48-14PostsynapticneuronSynapticterminalsof pre-synapticneurons5 m19Figure 48.14 Synaptic terminals on the cell body of a postsynaptic neuron (colorized SEM)

Fig. 48-15Voltage-gatedCa2+ channelCa2+1234SynapticcleftLigand-gatedion channelsPostsynapticmembranePresynapticmembraneSynaptic vesiclescontainingneurotransmitter56K+Na+20Figure 48.15 A chemical synapsePostsynaptic potentials fall into two categories:Excitatory postsynaptic potentials (EPSPs) are depolarizations that bring the membrane potential toward thresholdInhibitory postsynaptic potentials (IPSPs) are hyperpolarizations that move the membrane potential farther from thresholdPostsynaptic PotentialsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings21After release, the neurotransmitterMay diffuse out of the synaptic cleftMay be taken up by surrounding cells May be degraded by enzymesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings22Table 48-1

23Table 48.1Chapter 49Nervous SystemsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsPowerPoint Lecture Presentations for Biology Eighth EditionNeil Campbell and Jane ReeceLectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsOverview: Command and Control CenterThe circuits in the brain are more complex than the most powerful computersFunctional magnetic resonance imaging (MRI) can be used to construct a 3-D map of brain activityThe vertebrate brain is organized into regions with different functions

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsFig. 49-1

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings26Figure 49.1 How do scientists map activity within the human brain?For the Discovery Video Novelty Gene, go to Animation and Video Files.

Fig. 49-2(e) Insect (arthropod)SegmentalgangliaVentralnerve cordBrain(a) Hydra (cnidarian)Nerve netNerveringRadialnerve(b) Sea star (echinoderm)Anteriornerve ringLongitudinalnerve cords(f) Chiton (mollusc)(g) Squid (mollusc)GangliaBrainGanglia(c) Planarian (flatworm)NervecordsTransversenerveBrainEyespotBrain(d) Leech (annelid)SegmentalgangliaVentralnervecordBrainSpinalcord(dorsalnervecord)Sensoryganglia(h) Salamander (vertebrate)Concept 49.1: Nervous systems consist of circuits of neurons and supporting cellsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings27Figure 49.2 Nervous system organization

Fig. 49-3WhitematterCell body ofsensory neuron indorsal rootganglionSpinal cord(cross section)GraymatterHamstringmuscleQuadricepsmuscleSensory neuronMotor neuronInterneuronOrganization of the Vertebrate Nervous SystemCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings28Figure 49.3 The knee-jerk reflex

Fig. 49-4Peripheral nervoussystem (PNS)CranialnervesBrainCentral nervoussystem (CNS)GangliaoutsideCNSSpinalnervesSpinal cordCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings29Figure 49.4 The vertebrate nervous system

Fig. 49-5WhitematterVentriclesGray matterCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings30Figure 49.5 Ventricles, gray matter, and white matter

The central canal of the spinal cord and the ventricles of the brain are hollow and filled with cerebrospinal fluidThe cerebrospinal fluid is filtered from blood and functions to cushion the brain and spinal cord

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe brain and spinal cord contain Gray matter, which consists of neuron cell bodies, dendrites, and unmyelinated axons White matter, which consists of bundles of myelinated axons

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsGlia in the CNSGlia have numerous functionsEpendymal cells promote circulation of cerebrospinal fluidMicroglia protect the nervous system from microorganismsOligodendrocytes and Schwann cells form the myelin sheaths around axonsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsGlia have numerous functionsAstrocytes provide structural support for neurons, regulate extracellular ions and neurotransmitters, and induce the formation of a blood-brain barrier that regulates the chemical environment of the CNSRadial glia play a role in the embryonic development of the nervous system

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Fig. 49-6OligodendrocyteMicroglialcellSchwann cellsEpendy-malcellNeuronAstrocyteCNSPNSCapillary(a) Glia in vertebrates(b) Astrocytes (LM)VENTRICLE50 mCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings35Figure 49.6 Glia in the vertebrate nervous system

The Peripheral Nervous SystemThe PNS transmits information to and from the CNS and regulates movement and the internal environmentIn the PNS, afferent neurons transmit information to the CNS and efferent neurons transmit information away from the CNSCranial nerves originate in the brain and mostly terminate in organs of the head and upper bodySpinal nerves originate in the spinal cord and extend to parts of the body below the headCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-7-2EfferentneuronsLocomotionMotorsystemAutonomicnervous systemAfferent(sensory) neuronsPNSHearingCirculationGas exchangeDigestionHormoneactionEntericdivisionSympatheticdivisionParasympatheticdivisionCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings37Figure 49.7 Functional hierarchy of the vertebrate peripheral nervous system

The PNS has two functional components: the motor system and the autonomic nervous systemThe motor system carries signals to skeletal muscles and is voluntaryThe autonomic nervous system regulates the internal environment in an involuntary mannerCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe autonomic nervous system has sympathetic, parasympathetic, and enteric divisionsThe sympathetic and parasympathetic divisions have antagonistic effects on target organs Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe sympathetic division correlates with the fight-or-flight responseThe parasympathetic division promotes a return to rest and digestThe enteric division controls activity of the digestive tract, pancreas, and gallbladder

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Fig. 49-8Stimulates glucoserelease from liver;inhibits gallbladderDilates pupilof eyeParasympathetic divisionSympathetic divisionAction on target organs:Inhibits salivary gland secretionAccelerates heartRelaxes bronchiin lungsInhibits activityof stomach and intestinesInhibits activityof pancreasStimulatesadrenal medullaInhibits emptyingof bladderPromotes ejaculation and vaginal contractionsConstricts pupilof eyeStimulates salivarygland secretionConstrictsbronchi in lungsSlows heartStimulates activityof stomach andintestinesStimulates activityof pancreasStimulatesgallbladderPromotes emptyingof bladderPromotes erectionof genitalsAction on target organs:CervicalSympatheticgangliaThoracicLumbarSynapseSacralCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings41Figure 49.8 The parasympathetic and sympathetic divisions of the autonomic nervous system

Table 49-1Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings42Table 49.1

Concept 49.2: The vertebrate brain is regionally specializedAll vertebrate brains develop from three embryonic regions: forebrain, midbrain, and hindbrainBy the fifth week of human embryonic development, five brain regions have formed from the three embryonic regions

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Fig. 49-9Pons (part of brainstem), cerebellumForebrainMidbrainHindbrainMidbrainForebrainHindbrainTelencephalonTelencephalonDiencephalonDiencephalonMesencephalonMesencephalonMetencephalonMetencephalonMyelencephalonMyelencephalonSpinal cordSpinal cordCerebrum (includes cerebral cortex, white matter,basal nuclei)Diencephalon (thalamus, hypothalamus, epithalamus)Midbrain (part of brainstem)Medulla oblongata (part of brainstem)PituitaryglandCerebrumCerebellumCentral canalDiencephalon:HypothalamusThalamusPineal gland(part of epithalamus)Brainstem:MidbrainPonsMedullaoblongata(c) Adult(b) Embryo at 5 weeks(a) Embryo at 1 monthCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings44Figure 49.9 Development of the human brain

As a human brain develops further, the most profound change occurs in the forebrain, which gives rise to the cerebrumThe outer portion of the cerebrum called the cerebral cortex surrounds much of the brainCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-UN1Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings46The BrainstemThe brainstem coordinates and conducts information between brain centersThe brainstem has three parts: the midbrain, the pons, and the medulla oblongataCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe midbrain contains centers for receipt and integration of sensory informationThe pons regulates breathing centers in the medullaThe medulla oblongata contains centers that control several functions including breathing, cardiovascular activity, swallowing, vomiting, and digestion

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsArousal and SleepThe brainstem and cerebrum control arousal and sleepThe core of the brainstem has a diffuse network of neurons called the reticular formationThis regulates the amount and type of information that reaches the cerebral cortex and affects alertnessThe hormone melatonin is released by the pineal gland and plays a role in bird and mammal sleep cyclesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-10Input from touch,pain, and temperaturereceptorsReticular formationEyeInput from nervesof earsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings50Figure 49.10 The reticular formation

Sleep is essential and may play a role in the consolidation of learning and memoryDolphins sleep with one brain hemisphere at a time and are therefore able to swim while asleepCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-11High-frequency waves characteristic of wakefulnessLefthemisphereKeyTime: 0 hoursLow-frequency waves characteristic of sleepRighthemisphereLocationTime: 1 hourCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings52Figure 49.11 Dolphins can be asleep and awake at the same time

The CerebellumThe cerebellum is important for coordination and error checking during motor, perceptual, and cognitive functionsIt is also involved in learning and remembering motor skillsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-UN2Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings54The DiencephalonThe diencephalon develops into three regions: the epithalamus, thalamus, and hypothalamusThe epithalamus includes the pineal gland and generates cerebrospinal fluid from bloodThe thalamus is the main input center for sensory information to the cerebrum and the main output center for motor information leaving the cerebrumThe hypothalamus regulates homeostasis and basic survival behaviors such as feeding, fighting, fleeing, and reproducingCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-UN3Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings56Biological Clock Regulation by the HypothalamusThe hypothalamus also regulates circadian rhythms such as the sleep/wake cycleMammals usually have a pair of suprachiasmatic nuclei (SCN) in the hypothalamus that function as a biological clockBiological clocks usually require external cues to remain synchronized with environmental cyclesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-12BeforeproceduresRESULTSCircadian cycle period (hours)After surgeryand transplant hamsterWild-type hamsterWild-type hamster withSCN from hamster242023222119 hamster with SCNfrom wild-type hamsterCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings58Figure 49.12 Which cells control the circadian rhythm in mammals?

The CerebrumThe cerebrum develops from the embryonic telencephalon

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Fig. 49-UN4Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings60The cerebrum has right and left cerebral hemispheresEach cerebral hemisphere consists of a cerebral cortex (gray matter) overlying white matter and basal nucleiIn humans, the cerebral cortex is the largest and most complex part of the brainThe basal nuclei are important centers for planning and learning movement sequencesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsA thick band of axons called the corpus callosum provides communication between the right and left cerebral corticesThe right half of the cerebral cortex controls the left side of the body, and vice versa

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Fig. 49-13CorpuscallosumThalamusLeft cerebralhemisphereRight cerebralhemisphereCerebralcortexBasalnucleiCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings63Figure 49.13 The human brain viewed from the rear

Evolution of Cognition in VertebratesThe outermost layer of the cerebral cortex has a different arrangement in birds and mammalsIn mammals, the cerebral cortex has a convoluted surface called the neocortex, which was previously thought to be required for cognitionCognition is the perception and reasoning that form knowledgeHowever, it has recently been shown that birds also demonstrate cognition even though they lack a neocortexCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-14ThalamusCerebralcortexPalliumCerebrumThalamusCerebrumCerebellumCerebellumMidbrainMidbrainHindbrainHindbrainHuman brainAvian brainAvian brainto scaleCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings65Figure 49.14 Comparison of regions for higher cognition in avian and human brains

Concept 49.3: The cerebral cortex controls voluntary movement and cognitive functionsEach side of the cerebral cortex has four lobes: frontal, temporal, occipital, and parietal Each lobe contains primary sensory areas and association areas where information is integratedCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-15SpeechOccipital lobeVisionTemporal lobeFrontal lobeParietal lobeSomatosensoryassociationareaFrontalassociationareaVisualassociationareaReadingTasteHearingAuditoryassociationareaSpeechSmellMotor cortexSomatosensory cortexCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings67Figure 49.15 The human cerebral cortex

Information Processing in the Cerebral CortexThe cerebral cortex receives input from sensory organs and somatosensory receptorsSpecific types of sensory input enter the primary sensory areas of the brain lobesAdjacent areas process features in the sensory input and integrate information from different sensory areasIn the somatosensory and motor cortices, neurons are distributed according to the body part that generates sensory input or receives motor inputCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-16Primarysomatosensory cortexFrontal lobePharynxParietal lobeTeethGumsJawTongueLipsFaceNoseEyeThumbFingersHandForearmElbowUpper armHeadNeckTrunkHipLegGenitalsAbdominalorgansPrimarymotor cortexTongueToesJawLipsFaceEyeBrowNeckFingersHandWristForearmElbowShoulderTrunkHipKneeThumbCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings69Figure 49.16 Body part representation in the primary motor and primary somatosensory cortices

Language and SpeechStudies of brain activity have mapped areas responsible for language and speechBrocas area in the frontal lobe is active when speech is generatedWernickes area in the temporal lobe is active when speech is heardCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-17Generating wordsMaxSpeaking wordsHearing wordsSeeing wordsMinCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings71Figure 49.17 Mapping language areas in the cerebral cortex

Lateralization of Cortical FunctionThe corpus callosum transmits information between the two cerebral hemispheres The left hemisphere is more adept at language, math, logic, and processing of serial sequencesThe right hemisphere is stronger at pattern recognition, nonverbal thinking, and emotional processing

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe differences in hemisphere function are called lateralizationLateralization is linked to handednessCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsEmotionsEmotions are generated and experienced by the limbic system and other parts of the brain including the sensory areasThe limbic system is a ring of structures around the brainstem that includes the amygdala, hippocampus, and parts of the thalamusThe amygdala is located in the temporal lobe and helps store an emotional experience as an emotional memoryCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-18ThalamusHypothalamusPrefrontalcortexOlfactorybulbAmygdalaHippocampusCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings75Figure 49.18 The limbic systemFor the Discovery Video Teen Brains, go to Animation and Video Files.

ConsciousnessModern brain-imaging techniques suggest that consciousness is an emergent property of the brain based on activity in many areas of the cortexCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsConcept 49.4 Changes in synaptic connections underlie memory and learningTwo processes dominate embryonic development of the nervous systemNeurons compete for growth-supporting factors in order to surviveOnly half the synapses that form during embryo development survive into adulthoodCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsNeural PlasticityNeural plasticity describes the ability of the nervous system to be modified after birthChanges can strengthen or weaken signaling at a synapse

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Fig. 49-19(a) Synapses are strengthened or weakened in response to activity.N2(b) If two synapses are often active at the same time, the strength of the postsynaptic response may increase at both synapses.N1N2N1Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings79Figure 49.19 Neural plasticity

Memory and LearningLearning can occur when neurons make new connections or when the strength of existing neural connections changesShort-term memory is accessed via the hippocampusThe hippocampus also plays a role in forming long-term memory, which is stored in the cerebral cortexCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsLong-Term PotentiationIn the vertebrate brain, a form of learning called long-term potentiation (LTP) involves an increase in the strength of synaptic transmissionLTP involves glutamate receptorsIf the presynaptic and postsynaptic neurons are stimulated at the same time, the set of receptors present on the postsynaptic membranes changesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-20(c) Synapse exhibiting LTPMg2+Na+(a) Synapse prior to long-term potentiation (LTP)(b) Establishing LTPNMDA receptor(open)GlutamateStoredAMPAreceptorNMDAreceptor(closed)Ca2+1332142Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings82Figure 49.20 Long-term potentiation in the brain

Concept 49.5: Nervous system disorders can be explained in molecular termsDisorders of the nervous system include schizophrenia, depression, Alzheimers disease, and Parkinsons diseaseGenetic and environmental factors contribute to diseases of the nervous systemCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsSchizophreniaAbout 1% of the worlds population suffers from schizophreniaSchizophrenia is characterized by hallucinations, delusions, blunted emotions, and other symptomsAvailable treatments focus on brain pathways that use dopamine as a neurotransmitterCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-21Genes shared with relatives ofperson with schizophrenia12.5% (3rd-degree relative)100%50% (1st-degree relative)25% (2nd-degree relative)5040302010Risk of developing schizophrenia (%)Relationship to person with schizophreniaFraternal twinIdentical twinChildGrandchildFull siblingParentHalf siblingNephew/nieceUncle/auntFirst cousinIndividual,general population0Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings85Figure 49.21 Genetic contribution to schizophrenia

DepressionTwo broad forms of depressive illness are known: major depressive disorder and bipolar disorderIn major depressive disorder, patients have a persistent lack of interest or pleasure in most activitiesBipolar disorder is characterized by manic (high-mood) and depressive (low-mood) phasesTreatments for these types of depression include drugs such as Prozac and lithiumCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsDrug Addiction and the Brain Reward SystemThe brains reward system rewards motivation with pleasureSome drugs are addictive because they increase activity of the brains reward system These drugs include cocaine, amphetamine, heroin, alcohol, and tobaccoDrug addiction is characterized by compulsive consumption and an inability to control intakeCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsAddictive drugs enhance the activity of the dopamine pathwayDrug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drugCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-22Nicotinestimulatesdopamine-releasingVTA neuron.Cerebralneuron ofreward pathwayOpium and heroindecrease activityof inhibitoryneuron.Cocaine andamphetaminesblock removalof dopamine.RewardsystemresponseCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings89Figure 49.22 Effects of addictive drugs on the reward pathway of the mammalian brain

Alzheimers DiseaseAlzheimers disease is a mental deterioration characterized by confusion, memory loss, and other symptomsAlzheimers disease is caused by the formation of neurofibrillary tangles and amyloid plaques in the brainA successful treatment in humans may hinge on early detection of amyloid plaquesThere is no cure for this disease though some drugs are effective at relieving symptomsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-23Amyloid plaque20 mNeurofibrillary tangleCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings91Figure 49.23 Microscopic signs of Alzheimers disease

Parkinsons DiseaseParkinsons disease is a motor disorder caused by death of dopamine-secreting neurons in the midbrainIt is characterized by difficulty in initiating movements, muscle tremors, slowness of movement, and rigidityThere is no cure, although drugs and various other approaches are used to manage symptomsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsStem CellBased TherapyUnlike the PNS, the CNS cannot fully repair itselfHowever, it was recently discovered that the adult human brain contains stem cells that can differentiate into mature neuronsInduction of stem cell differentiation and transplantation of cultured stem cells are potential methods for replacing neurons lost to trauma or diseaseCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 49-2410 mCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings94Figure 49.24 A newly born neuron in the hippocampus of a human adult

Fig. 49-UN5CerebrumThalamusHypothalamusPituitary glandForebrainCerebralcortexMidbrainHindbrainPonsMedullaoblongataCerebellumSpinalcordCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings95Chapter 50Sensory and Motor MechanismsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsPowerPoint Lecture Presentations for Biology Eighth EditionNeil Campbell and Jane ReeceLectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings96Overview: Sensing and ActingBats use sonar to detect their preyMoths, a common prey for bats, can detect the bats sonar and attempt to fleeBoth organisms have complex sensory systems that facilitate survivalThese systems include diverse mechanisms that sense stimuli and generate appropriate movement

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Fig. 50-1Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings98Figure 50.1 Can a moth evade a bat in the dark?Concept 50.1: Sensory receptors transduce stimulus energy and transmit signals to the central nervous systemAll stimuli represent forms of energySensation involves converting energy into a change in the membrane potential of sensory receptorsSensations are action potentials that reach the brain via sensory neuronsThe brain interprets sensations, giving the perception of stimuliCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings99Sensory PathwaysFunctions of sensory pathways: sensory reception, transduction, transmission, and integrationFor example, stimulation of a stretch receptor in a crayfish is the first step in a sensory pathway

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Fig. 50-2Slight bend:weakstimulusStretchreceptorMembranepotential (mV)AxonDendritesStrong receptorpotentialWeakreceptorpotentialMuscle5070Membranepotential (mV)5070Action potentialsAction potentialsMembranepotential (mV)Large bend:strongstimulusReceptionTransduction0700701 2 3 4 5 6 7Membranepotential (mV)Time (sec)1 2 3 4 5 6 7Time (sec)TransmissionPerceptionBrainBrain perceiveslarge bend.Brain perceivesslight bend.1234123400Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings101Figure 50.2 A simple sensory pathway: Response of a crayfish stretch receptor to bendingSensory Reception and TransductionSensations and perceptions begin with sensory reception, detection of stimuli by sensory receptorsSensory receptors can detect stimuli outside and inside the bodyCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings102Sensory transduction is the conversion of stimulus energy into a change in the membrane potential of a sensory receptorThis change in membrane potential is called a receptor potentialMany sensory receptors are very sensitive: they are able to detect the smallest physical unit of stimulusFor example, most light receptors can detect a photon of lightCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings103TransmissionAfter energy has been transduced into a receptor potential, some sensory cells generate the transmission of action potentials to the CNSSensory cells without axons release neurotransmitters at synapses with sensory neuronsLarger receptor potentials generate more rapid action potentialsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings104Integration of sensory information begins when information is receivedSome receptor potentials are integrated through summationCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings105PerceptionPerceptions are the brains construction of stimuliStimuli from different sensory receptors travel as action potentials along different neural pathwaysThe brain distinguishes stimuli from different receptors by the area in the brain where the action potentials arriveCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings106Amplification and AdaptationAmplification is the strengthening of stimulus energy by cells in sensory pathwaysSensory adaptation is a decrease in responsiveness to continued stimulationCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings107Types of Sensory ReceptorsBased on energy transduced, sensory receptors fall into five categories:MechanoreceptorsChemoreceptorsElectromagnetic receptorsThermoreceptorsPain receptors (nociceptors)Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings108MechanoreceptorsMechanoreceptors sense physical deformation caused by stimuli such as pressure, stretch, motion, and soundThe sense of touch in mammals relies on mechanoreceptors that are dendrites of sensory neuronsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings109

Fig. 50-3ConnectivetissueHeatStrongpressureHairmovementNerveDermisEpidermisHypodermisGentletouchPainColdHairCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings110Figure 50.3 Sensory receptors in human skin

ChemoreceptorsGeneral chemoreceptors transmit information about the total solute concentration of a solutionSpecific chemoreceptors respond to individual kinds of moleculesWhen a stimulus molecule binds to a chemoreceptor, the chemoreceptor becomes more or less permeable to ions The antennae of the male silkworm moth have very sensitive specific chemoreceptorsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings111

Fig. 50-40.1 mmCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings112Figure 50.4 Chemoreceptors in an insect

Electromagnetic ReceptorsElectromagnetic receptors detect electromagnetic energy such as light, electricity, and magnetismPhotoreceptors are electromagnetic receptors that detect lightSome snakes have very sensitive infrared receptors that detect body heat of prey against a colder backgroundCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings113

Fig. 50-5(a) Rattlesnake(b) Beluga whalesEyeInfraredreceptorCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings114Figure 50.5 Specialized electromagnetic receptorsThermoreceptorsThermoreceptors, which respond to heat or cold, help regulate body temperature by signaling both surface and body core temperatureCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings115Pain ReceptorsIn humans, pain receptors, or nociceptors, are a class of naked dendrites in the epidermisThey respond to excess heat, pressure, or chemicals released from damaged or inflamed tissuesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings116Concept 50.2: The mechanoreceptors responsible for hearing and equilibrium detect moving fluid or settling particlesHearing and perception of body equilibrium are related in most animalsSettling particles or moving fluid are detected by mechanoreceptors Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings117

Fig. 50-6Sensory axonsStatolithCiliaCiliatedreceptor cellsSensing Gravity and Sound in InvertebratesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings118Figure 50.6 The statocyst of an invertebrate

Fig. 50-71 mmTympanicmembraneCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings119Figure 50.7 An insect earon its leg

Fig. 50-8Hair cell bundle froma bullfrog; the longestcilia shown areabout 8 m (SEM).AuditorycanalEustachiantubePinnaTympanicmembraneOvalwindowRoundwindowStapesCochleaTectorialmembraneIncusMalleusSemicircularcanalsAuditory nerveto brainSkullboneOuter earMiddleearInner earCochlearductVestibularcanalBoneTympaniccanalAuditorynerveOrgan of CortiTo auditorynerveAxons ofsensory neuronsBasilarmembraneHair cellsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings120Figure 50.8 The structure of the human ear

Fig. 50-10Axons ofsensory neuronsVibrationBasilar membraneBasilar membraneApexApexOvalwindowFlexible end ofbasilar membraneVestibularcanal500 Hz(low pitch)16 kHz(high pitch)StapesBaseRoundwindowTympaniccanalFluid(perilymph)Base(stiff)8 kHz4 kHz2 kHz1 kHz{{HearingCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings121Figure 50.10 Transduction in the cochlea

Fig. 50-11Vestibular nerveSemicircular canalsSacculeUtricleBody movementHairsCupulaFlow of fluidAxonsHaircellsVestibuleEquilibriumCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings122Figure 50.11 Organs of equilibrium in the inner ear

Fig. 50-12Surrounding waterLateral lineLateral line canalEpidermisHair cellCupulaAxonSensoryhairsScaleLateral nerveOpening oflateral line canalSegmental musclesFish body wallSupportingcellHearing and Equilibrium in Other VertebratesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings123Figure 50.12 The lateral line system in a fishConcept 50.3: The senses of taste and smell rely on similar sets of sensory receptorsIn terrestrial animals:Gustation (taste) is dependent on the detection of chemicals called tastantsOlfaction (smell) is dependent on the detection of odorant moleculesIn aquatic animals there is no distinction between taste and smellTaste receptors of insects are in sensory hairs called sensilla, located on feet and in mouth partsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings124Taste in MammalsIn humans, receptor cells for taste are modified epithelial cells organized into taste budsThere are five taste perceptions: sweet, sour, salty, bitter, and umami (elicited by glutamate)Each type of taste can be detected in any region of the tongueCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings125

Fig. 50-13G proteinSugar moleculePhospholipase CTongueSodiumchannelPIP2Na+IP3(secondmessenger)SweetreceptorERNucleusTaste poreSENSORYRECEPTORCELLCa2+(secondmessenger)IP3-gatedcalciumchannelSensoryreceptorcellsTastebudSugarmoleculeSensoryneuronCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings126Figure 50.13 Sensory transduction by a sweet receptorSmell in HumansOlfactory receptor cells are neurons that line the upper portion of the nasal cavityBinding of odorant molecules to receptors triggers a signal transduction pathway, sending action potentials to the brain

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Fig. 50-15OlfactorybulbOdorantsBoneEpithelialcellPlasmamembraneOdorantreceptorsOdorantsNasal cavityBrainChemo-receptorCiliaMucusAction potentialsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings128Figure 50.15 Smell in humansConcept 50.4: Similar mechanisms underlie vision throughout the animal kingdomMany types of light detectors have evolved in the animal kingdomCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings129Vision in InvertebratesMost invertebrates have a light-detecting organOne of the simplest is the eye cup of planarians, which provides information about light intensity and direction but does not form imagesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings130

Fig. 50-16Nerve tobrainOcellusScreeningpigmentLightOcellusVisual pigmentPhotoreceptorCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings131Figure 50.16 Ocelli and orientation behavior of a planarianTwo major types of image-forming eyes have evolved in invertebrates: the compound eye and the single-lens eyeCompound eyes are found in insects and crustaceans and consist of up to several thousand light detectors called ommatidiaCompound eyes are very effective at detecting movementCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings132

Fig. 50-17Rhabdom(a) Fly eyesCrystallineconeLens(b) OmmatidiaOmmatidiumPhotoreceptorAxonsCornea2 mmCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings133Figure 50.17 Compound eyesSingle-lens eyes are found in some jellies, polychaetes, spiders, and many molluscsThey work on a camera-like principle: the iris changes the diameter of the pupil to control how much light entersCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings134

Fig. 50-18OpticnerveFovea (centerof visual field)LensVitreous humorOptic disk(blind spot)Central artery andvein of the retinaIrisRetinaChoroidScleraCiliary bodySuspensoryligamentCorneaPupilAqueoushumorStructure of the EyeCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings135Figure 50.18 Structure of the vertebrate eye

Fig. 50-20RodOutersegmentRhodopsinDisksSynapticterminalCell bodytrans isomerRetinalOpsinLightcis isomerEnzymesCYTOSOLINSIDEOF DISKSensory Transduction in the EyeCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings136Figure 50.20 Activation of rhodopsin by light

Fig. 50-21LightSodiumchannelInactive rhodopsinActive rhodopsinPhosphodiesteraseDiskmembraneINSIDE OF DISKPlasmamembraneEXTRACELLULARFLUIDLightTransducinCYTOSOLGMPcGMPNa+Na+DarkTimeHyper-polarization0Membranepotential (mV)4070Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings137Figure 50.21 Receptor potential production in a rod cellIn humans, three pigments called photopsins detect light of different wave lengths: red, green, or blue

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings138Concept 50.5: The physical interaction of protein filaments is required for muscle functionMuscle activity is a response to input from the nervous systemThe action of a muscle is always to contract

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Fig. 50-25Bundle ofmuscle fibersTEMMuscleThickfilaments(myosin)M lineSingle muscle fiber(cell)NucleiZ linesPlasma membraneMyofibrilSarcomereZ lineZ lineThinfilaments(actin)Sarcomere0.5 mVertebrate Skeletal MuscleCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings140Figure 50.25 The structure of skeletal muscle

The Sliding-Filament Model of Muscle ContractionAccording to the sliding-filament model, filaments slide past each other longitudinally, producing more overlap between thin and thick filamentsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings141

Fig. 50-26ZRelaxedmuscleM Z Fully contractedmuscleContractingmuscleSarcomere0.5 mContractedSarcomereCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings142Figure 50.26 The sliding-filament model of muscle contractionFor the Cell Biology Video Conformational Changes in Calmodulin, go to Animation and Video Files.For the Cell Biology Video Cardiac Muscle Contraction, go to Animation and Video Files.

The sliding of filaments is based on interaction between actin of the thin filaments and myosin of the thick filamentsThe head of a myosin molecule binds to an actin filament, forming a cross-bridge and pulling the thin filament toward the center of the sarcomereGlycolysis and aerobic respiration generate the ATP needed to sustain muscle contractionCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings143

Fig. 50-27-4ThinfilamentsATP Myosin head (low-energy configurationThick filamentThin filamentThickfilamentActinMyosin head (high-energy configurationMyosin binding sitesADPP iCross-bridgeADPP iMyosin head (low-energy configurationThin filament movestoward center of sarcomere.ATP ADPP i+Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings144Figure 50.27 Myosin-actin interactions underlying muscle fiber contraction

The Role of Calcium and Regulatory ProteinsA skeletal muscle fiber contracts only when stimulated by a motor neuronWhen a muscle is at rest, myosin-binding sites on the thin filament are blocked by the regulatory protein tropomyosinCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings145

Fig. 50-28Myosin-binding siteTropomyosin(a) Myosin-binding sites blocked(b) Myosin-binding sites exposedCa2+Ca2+-binding sitesTroponin complexActinCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings146Figure 50.28 The role of regulatory proteins and calcium in muscle fiber contractionFor a muscle fiber to contract, myosin-binding sites must be uncoveredThis occurs when calcium ions (Ca2+) bind to a set of regulatory proteins, the troponin complexMuscle fiber contracts when the concentration of Ca2+ is high; muscle fiber contraction stops when the concentration of Ca2+ is lowCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings147The stimulus leading to contraction of a muscle fiber is an action potential in a motor neuron that makes a synapse with the muscle fiberCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings148

Fig. 50-29SarcomereCa2+ATPasepump

Ca2+ released from SRSynapticterminalT tubuleMotorneuron axonPlasma membraneof muscle fiberSarcoplasmicreticulum (SR)MyofibrilSynaptic terminalof motor neuronMitochondrionSynaptic cleftT TubulePlasma membraneCa2+Ca2+CYTOSOLSRATPADPP iAChCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings149Figure 50.29 The regulation of skeletal muscle contractionThe synaptic terminal of the motor neuron releases the neurotransmitter acetylcholineAcetylcholine depolarizes the muscle, causing it to produce an action potential

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings150Action potentials travel to the interior of the muscle fiber along transverse (T) tubulesThe action potential along T tubules causes the sarcoplasmic reticulum (SR) to release Ca2+The Ca2+ binds to the troponin complex on the thin filamentsThis binding exposes myosin-binding sites and allows the cross-bridge cycle to proceedCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings151Other Types of MuscleIn addition to skeletal muscle, vertebrates have cardiac muscle and smooth muscleCardiac muscle, found only in the heart, consists of striated cells electrically connected by intercalated disksCardiac muscle can generate action potentials without neural inputCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings152In smooth muscle, found mainly in walls of hollow organs, contractions are relatively slow and may be initiated by the muscles themselvesContractions may also be caused by stimulation from neurons in the autonomic nervous systemCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings153Concept 50.6: Skeletal systems transform muscle contraction into locomotionSkeletal muscles are attached in antagonistic pairs, with each member of the pair working against the other The skeleton provides a rigid structure to which muscles attachSkeletons function in support, protection, and movementCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings154

Fig. 50-32GrasshopperHumanBicepscontractsTricepscontractsForearmextendsBicepsrelaxesTricepsrelaxesForearmflexesTibiaflexesTibiaextendsFlexormusclerelaxesFlexormusclecontractsExtensormusclecontractsExtensormusclerelaxesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings155Figure 50.32 The interaction of muscles and skeletons in movementFor the Discovery Video Muscles and Bones, go to Animation and Video Files.

Types of Skeletal SystemsThe three main types of skeletons are: Hydrostatic skeletons (lack hard parts)Exoskeletons (external hard parts)Endoskeletons (internal hard parts)Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings156Hydrostatic SkeletonsA hydrostatic skeleton consists of fluid held under pressure in a closed body compartmentThis is the main type of skeleton in most cnidarians, flatworms, nematodes, and annelidsAnnelids use their hydrostatic skeleton for peristalsis, a type of movement on land produced by rhythmic waves of muscle contractionsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings157

Fig. 50-33CircularmusclecontractedCircularmusclerelaxedLongitudinalmuscle relaxed(extended)LongitudinalmusclecontractedBristlesHead endHead endHead endCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings158Figure 50.33 Crawling by peristalsisExoskeletonsAn exoskeleton is a hard encasement deposited on the surface of an animalExoskeletons are found in most molluscs and arthropodsArthropod exoskeletons are made of cuticle and can be both strong and flexibleThe polysaccharide chitin is often found in arthropod cuticleCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings159EndoskeletonsAn endoskeleton consists of hard supporting elements, such as bones, buried in soft tissue Endoskeletons are found in sponges, echinoderms, and chordatesA mammalian skeleton has more than 200 bonesSome bones are fused; others are connected at joints by ligaments that allow freedom of movementCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings160

Fig. 50-34Examplesof jointsHumerusBall-and-socket jointRadiusScapulaHead ofhumerusUlnaHinge jointUlnaPivot jointSkullShouldergirdleRibSternumClavicleScapulaVertebraHumerusPhalangesRadiusPelvicgirdleUlnaCarpalsMetacarpalsFemurPatellaTibiaFibulaTarsalsMetatarsalsPhalanges112332Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings161Figure 50.34 Bones and joints of the human skeletonSize and Scale of SkeletonsAn animals body structure must support its sizeThe size of an animals body scales with volume (a function of n3), while the support for that body scales with cross-sectional area of the legs (a function of n2)As objects get larger, size (n3) increases faster than cross-sectional area (n2); this is the principle of scalingCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings162The skeletons of small and large animals have different proportions because of the principle of scalingIn mammals and birds, the position of legs relative to the body is very important in determining how much weight the legs can bear

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