50 Lecture Presentation

Fig. 50-1

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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 stimuli


Sensory 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

Fig. 50-2Slight bend: weak stimulusStretch receptorMembrane potential (mV)AxonDendritesStrong receptor potentialWeak receptor potentialMuscle5070Membrane potential (mV)5070Action potentialsAction potentialsMembrane potential (mV)Large bend: strong stimulusReceptionTransduction0700701 2 3 4 5 6 7Membrane potential (mV)Time (sec)1 2 3 4 5 6 7Time (sec)TransmissionPerceptionBrainBrain perceives large bend.Brain perceives slight bend.1234123400


Sensory Reception and TransductionSensations and perceptions begin with sensory reception, detection of stimuli by sensory receptorsSensory receptors can detect stimuli outside and inside the body


Sensory 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 light


TransmissionAfter 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 potentials


Integration of sensory information begins when information is receivedSome receptor potentials are integrated through summation


PerceptionPerceptions 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 arrive


Amplification and AdaptationAmplification is the strengthening of stimulus energy by cells in sensory pathwaysSensory adaptation is a decrease in responsiveness to continued stimulation


Types of Sensory ReceptorsBased on energy transduced, sensory receptors fall into five categories:MechanoreceptorsChemoreceptorsElectromagnetic receptorsThermoreceptorsPain receptors


MechanoreceptorsMechanoreceptors 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 neurons

Fig. 50-3Connective tissueHeatStrong pressureHair movementNerveDermisEpidermisHypodermisGentle touchPainColdHair


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 chemoreceptors

Fig. 50-40.1 mm


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 background

Fig. 50-5(a) Rattlesnake(b) Beluga whalesEyeInfrared receptor

Fig. 50-5a(a) RattlesnakeEyeInfrared receptor


Many mammals appear to use Earths magnetic field lines to orient themselves as they migrate

Fig. 50-5b(b) Beluga whales


ThermoreceptorsThermoreceptors, which respond to heat or cold, help regulate body temperature by signaling both surface and body core temperature


Pain 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 tissues


Concept 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


Sensing Gravity and Sound in InvertebratesMost invertebrates maintain equilibrium using sensory organs called statocystsStatocysts contain mechanoreceptors that detect the movement of granules called statoliths

Fig. 50-6Sensory axonsStatolithCiliaCiliated receptor cells


Many arthropods sense sounds with body hairs that vibrate or with localized ears consisting of a tympanic membrane and receptor cells

Fig. 50-71 mmTympanic membrane


Hearing and Equilibrium in MammalsIn most terrestrial vertebrates, sensory organs for hearing and equilibrium are closely associated in the ear

Fig. 50-8Hair cell bundle from a bullfrog; the longest cilia shown are about 8 m (SEM).Auditory canalEustachian tubePinnaTympanic membraneOval windowRound windowStapesCochleaTectorial membraneIncusMalleusSemicircular canalsAuditory nerve to brainSkull boneOuter earMiddle earInner earCochlear ductVestibular canalBoneTympanic canalAuditory nerveOrgan of CortiTo auditory nerveAxons of sensory neuronsBasilar membraneHair cells

Fig. 50-8aAuditory canalEustachian tubePinnaTympanic membraneOval windowRound windowStapesCochleaIncusMalleusSemicircular canalsAuditory nerve to brainSkull boneOuter earMiddle earInner ear

Fig. 50-8bCochlear ductVestibular canalBoneTympanic canalAuditory nerveOrgan of Corti

Fig. 50-8cTectorial membraneTo auditory nerveAxons of sensory neuronsBasilar membraneHair cells

Fig. 50-8dHair cell bundle from a bullfrog; the longest cilia shown are about 8 m (SEM).


HearingVibrating objects create percussion waves in the air that cause the tympanic membrane to vibrateHearing is the perception of sound in the brain from the vibration of air wavesThe three bones of the middle ear transmit the vibrations of moving air to the oval window on the cochlea


These vibrations create pressure waves in the fluid in the cochlea that travel through the vestibular canalPressure waves in the canal cause the basilar membrane to vibrate, bending its hair cellsThis bending of hair cells depolarizes the membranes of mechanoreceptors and sends action potentials to the brain via the auditory nerve

Fig. 50-9Hairs of hair cellNeuro- transmitter at synapseSensory neuronMore neuro- trans- mitter(a) No bending of hairs(b) Bending of hairs in one direction(c) Bending of hairs in other directionLess neuro- trans- mitterAction potentialsMembrane potential (mV)0700 1 2 3 4 5 6 7Time (sec)SignalSignal7050Receptor potentialMembrane potential (mV)0700 1 2 3 4 5 6 7Time (sec)7050Membrane potential (mV)0700 1 2 3 4 5 6 7Time (sec)7050Signal

Fig. 50-9aHairs of hair cellNeuro- transmitter at synapseSensory neuron(a) No bending of hairsAction potentialsMembrane potential (mV)070Time (sec)Signal7050

Fig. 50-9bMore neuro- trans- mitter(b) Bending of hairs in one directionReceptor potentialMembrane potential (mV)070Time (sec)Signal7050

Fig. 50-9cLess neuro- trans- mitter(c) Bending of hairs in other directionMembrane potential (mV)070Time (sec)Signal7050


The fluid waves dissipate when they strike the round window at the end of the tympanic canal

Fig. 50-10Axons of sensory neuronsVibrationBasilar membraneBasilar membraneApexApexOval windowFlexible end of basilar membraneVestibular canal500 Hz (low pitch)16 kHz (high pitch)StapesBaseRound windowTympanic canalFluid (perilymph)Base (stiff)8 kHz4 kHz2 kHz1 kHz{{

Fig. 50-10aAxons of sensory neuronsVibrationBasilar membraneApexOval windowVestibular canalStapesBaseRound windowTympanic canalFluid (perilymph)


The ear conveys information about:Volume, the amplitude of the sound wavePitch, the frequency of the sound waveThe cochlea can distinguish pitch because the basilar membrane is not uniform along its lengthEach region vibrates most vigorously at a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex

Fig. 50-10bBasilar membraneApexFlexible end of basilar membrane500 Hz (low pitch)16 kHz (high pitch)Base (stiff)8 kHz4 kHz2 kHz1 kHz


EquilibriumSeveral organs of the inner ear detect body position and balance: The utricle and saccule contain granules called otoliths that allow us to detect gravity and linear movementThree semicircular canals contain fluid and allow us to detect angular acceleration such as the turning of the head

Fig. 50-11Vestibular nerveSemicircular canalsSacculeUtricleBody movementHairsCupulaFlow of fluidAxonsHair cellsVestibule


Hearing and Equilibrium in Other VertebratesUnlike mammals, fishes have only a pair of inner ears near the brainMost fishes and aquatic amphibians also have a lateral line system along both sides of their bodyThe lateral line system contains mechanoreceptors with hair cells that detect and respond to water movement

Fig. 50-12Surrounding waterLateral lineLateral line canalEpidermisHair cellCupulaAxonSensory hairsScaleLateral nerveOpening of lateral line canalSegmental musclesFish body wallSupporting cell


Concept 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 parts


Taste 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 tongue

Fig. 50-13G proteinSugar moleculePhospholipase CTongueSodium channelPIP2Na+IP3 (second messenger)Sweet receptorERNucleusTaste poreSENSORY RECEPTOR CELLCa2+ (second messenger)IP3-gated calcium channelSensory receptor cellsTaste budSugar moleculeSensory neuron


When a taste receptor is stimulated, the signal is transduced to a sensory neuronEach taste cell has only one type of receptor

Fig. 50-14PBDG receptor expression in cells for sweet tasteRelative consumption (%)Concentration of PBDG (mM); log scaleNo PBDG receptor gene PBDG receptor expression in cells for bitter taste 0.1 1 1080 60 4020RESULTS


Smell 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

Fig. 50-15Olfactory bulbOdorantsBoneEpithelial cellPlasma membraneOdorant receptorsOdorantsNasal cavityBrainChemo- receptorCiliaMucusAction potentials


Concept 50.4: Similar mechanisms underlie vision throughout the animal kingdomMany types of light detectors have evolved in the animal kingdom


Vision 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 images

Fig. 50-16Nerve to brainOcellusScreening pigmentLightOcellusVisual pigmentPhotoreceptor


Two 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 movement

Fig. 50-17Rhabdom(a) Fly eyesCrystalline coneLens(b) OmmatidiaOmmatidiumPhotoreceptorAxonsCornea2 mm

Fig. 50-17a(a) Fly eyes2 mm

Fig. 50-17bRhabdomCrystalline coneLens(b) OmmatidiaOmmatidiumPhotoreceptorAxonsCornea


Single-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 enters


The Vertebrate Visual SystemIn vertebrates the eye detects color and light, but the brain assembles the information and perceives the image


Structure of the EyeMain parts of the vertebrate eye:The sclera: white outer layer, including corneaThe choroid: pigmented layerThe iris: regulates the size of the pupilThe retina: contains photoreceptorsThe lens: focuses light on the retinaThe optic disk: a blind spot in the retina where the optic nerve attaches to the eye


The eye is divided into two cavities separated by the lens and ciliary body:The anterior cavity is filled with watery aqueous humorThe posterior cavity is filled with jellylike vitreous humorThe ciliary body produces the aqueous humor

Fig. 50-18Optic nerveFovea (center of visual field)LensVitreous humorOptic disk (blind spot)Central artery and vein of the retinaIrisRetinaChoroidScleraCiliary bodySuspensory ligamentCorneaPupilAqueous humor


Humans and other mammals focus light by changing the shape of the lensAnimation: Near and Distance Vision

Fig. 50-19Ciliary muscles relax.RetinaChoroid(b) Distance vision(a) Near vision (accommodation)Suspensory ligaments pull against lens.Lens becomes flatter.Lens becomes thicker and rounder.Ciliary muscles contract.Suspensory ligaments relax.


The human retina contains two types of photoreceptors: rods and conesRods are light-sensitive but dont distinguish colorsCones distinguish colors but are not as sensitive to lightIn humans, cones are concentrated in the fovea, the center of the visual field, and rods are more concentrated around the periphery of the retina


Sensory Transduction in the EyeEach rod or cone contains visual pigments consisting of a light-absorbing molecule called retinal bonded to a protein called an opsinRods contain the pigment rhodopsin (retinal combined with a specific opsin), which changes shape when absorbing light

Fig. 50-20RodOuter segmentRhodopsinDisksSynaptic terminalCell bodytrans isomerRetinalOpsinLightcis isomerEnzymesCYTOSOLINSIDE OF DISK


Once light activates rhodopsin, cyclic GMP breaks down, and Na+ channels closeThis hyperpolarizes the cell

Fig. 50-21LightSodium channelInactive rhodopsinActive rhodopsinPhosphodiesteraseDisk membraneINSIDE OF DISKPlasma membraneEXTRACELLULAR FLUIDLightTransducinCYTOSOLGMPcGMPNa+Na+DarkTimeHyper- polarization0Membrane potential (mV)4070


In humans, three pigments called photopsins detect light of different wave lengths: red, green, or blue


Processing of Visual InformationProcessing of visual information begins in the retinaAbsorption of light by retinal triggers a signal transduction pathway

Fig. 50-22Light ResponsesRod depolarizedRhodopsin inactiveRhodopsin activeDark ResponsesNa+ channels openNa+ channels closedGlutamate releasedBipolar cell either depolarized or hyperpolarizedRod hyperpolarizedNo glutamate releasedBipolar cell either hyperpolarized or depolarized


In the dark, rods and cones release the neurotransmitter glutamate into synapses with neurons called bipolar cellsBipolar cells are either hyperpolarized or depolarized in response to glutamateIn the light, rods and cones hyperpolarize, shutting off release of glutamateThe bipolar cells are then either depolarized or hyperpolarized


Three other types of neurons contribute to information processing in the retinaGanglion cells transmit signals from bipolar cells to the brain; these signals travel along the optic nerves, which are made of ganglion cell axonsHorizontal cells and amacrine cells help integrate visual information before it is sent to the brainInteraction among different cells results in lateral inhibition, a greater contrast in image

Fig. 50-23RetinaRetinaPhotoreceptorsLightOptic nerveLightTo brainChoroidNeuronsConeRodGanglion cellOptic nerve axonsAmacrine cellHorizontal cellBipolar cellPigmented epithelium


The optic nerves meet at the optic chiasm near the cerebral cortexHere, axons from the left visual field (from both the left and right eye) converge and travel to the right side of the brainLikewise, axons from the right visual field travel to the left side of the brain


Most ganglion cell axons lead to the lateral geniculate nucleiThe lateral geniculate nuclei relay information to the primary visual cortex in the cerebrumSeveral integrating centers in the cerebral cortex are active in creating visual perceptions

Fig. 50-24Right visual fieldRight eyeLeft visual fieldLeft eyeOptic chiasmPrimary visual cortexLateral geniculate nucleusOptic nerve


Evolution of Visual PerceptionPhotoreceptors in diverse animals likely originated in the earliest bilateral animalsMelanopsin, a pigment in ganglion cells, may play a role in circadian rhythms in humans


Concept 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


Vertebrate Skeletal MuscleVertebrate skeletal muscle is characterized by a hierarchy of smaller and smaller unitsA skeletal muscle consists of a bundle of long fibers, each a single cell, running parallel to the length of the muscleEach muscle fiber is itself a bundle of smaller myofibrils arranged longitudinally


The myofibrils are composed to two kinds of myofilaments:Thin filaments consist of two strands of actin and one strand of regulatory proteinThick filaments are staggered arrays of myosin molecules


Skeletal muscle is also called striated muscle because the regular arrangement of myofilaments creates a pattern of light and dark bandsThe functional unit of a muscle is called a sarcomere, and is bordered by Z lines

Fig. 50-25Bundle of muscle fibersTEMMuscleThick filaments (myosin)M lineSingle muscle fiber (cell)NucleiZ linesPlasma membraneMyofibrilSarcomereZ lineZ lineThin filaments (actin)Sarcomere0.5 m

Fig. 50-25aBundle of muscle fibersMuscleSingle muscle fiber (cell)NucleiZ linesPlasma membraneMyofibrilSarcomere

Fig. 50-25bTEMThick filaments (myosin)M lineZ lineZ lineThin filaments (actin)Sarcomere0.5 m


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 filaments

Fig. 50-26ZRelaxed muscleM Z Fully contracted muscleContracting muscleSarcomere0.5 mContracted Sarcomere


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 contraction

Fig. 50-27-1Thin filamentsATP Myosin head (low- energy configurationThick filamentThin filamentThick filament

Fig. 50-27-2Thin filamentsATP Myosin head (low- energy configurationThick filamentThin filamentThick filamentActinMyosin head (high- energy configurationMyosin binding sitesADPP i

Fig. 50-27-3Thin filamentsATP Myosin head (low- energy configurationThick filamentThin filamentThick filamentActinMyosin head (high- energy configurationMyosin binding sitesADPP iCross-bridgeADPP i

Fig. 50-27-4Thin filamentsATP Myosin head (low- energy configurationThick filamentThin filamentThick filamentActinMyosin head (high- energy configurationMyosin binding sitesADPP iCross-bridgeADPP iMyosin head (low- energy configurationThin filament moves toward center of sarcomere.ATP ADPP i+


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 tropomyosin

Fig. 50-28Myosin- binding siteTropomyosin(a) Myosin-binding sites blocked(b) Myosin-binding sites exposedCa2+Ca2+-binding sitesTroponin complexActin


For 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 low


The stimulus leading to contraction of a muscle fiber is an action potential in a motor neuron that makes a synapse with the muscle fiber

Fig. 50-29SarcomereCa2+ ATPase pump Ca2+ released from SRSynaptic terminalT tubuleMotor neuron axonPlasma membrane of muscle fiberSarcoplasmic reticulum (SR)MyofibrilSynaptic terminal of motor neuronMitochondrionSynaptic cleftT TubulePlasma membraneCa2+Ca2+CYTOSOLSRATPADPP iACh

Fig. 50-29aSarcomereCa2+ released from SRSynaptic terminalT tubuleMotor neuron axonPlasma membrane of muscle fiberSarcoplasmic reticulum (SR)MyofibrilMitochondrion


The synaptic terminal of the motor neuron releases the neurotransmitter acetylcholineAcetylcholine depolarizes the muscle, causing it to produce an action potential

Fig. 50-29bCa2+ ATPase pump Synaptic terminal of motor neuronSynaptic cleftT TubulePlasma membraneCa2+Ca2+CYTOSOLSRATPADPP iACh


Action 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 proceed


Amyotrophic lateral sclerosis (ALS), formerly called Lou Gehrigs disease, interferes with the excitation of skeletal muscle fibers; this disease is usually fatalMyasthenia gravis is an autoimmune disease that attacks acetylcholine receptors on muscle fibers; treatments exist for this disease


Nervous Control of Muscle TensionContraction of a whole muscle is graded, which means that the extent and strength of its contraction can be voluntarily alteredThere are two basic mechanisms by which the nervous system produces graded contractions:Varying the number of fibers that contractVarying the rate at which fibers are stimulated


In a vertebrate skeletal muscle, each branched muscle fiber is innervated by one motor neuronEach motor neuron may synapse with multiple muscle fibersA motor unit consists of a single motor neuron and all the muscle fibers it controls

Fig. 50-30Spinal cordMotor neuron cell bodyMotor neuron axonNerveMuscleMuscle fibersSynaptic terminalsTendonMotor unit 1Motor unit 2


Recruitment of multiple motor neurons results in stronger contractionsA twitch results from a single action potential in a motor neuronMore rapidly delivered action potentials produce a graded contraction by summation

Fig. 50-31Summation of two twitchesTetanusSingle twitchTimeTensionPair of action potentialsAction potentialSeries of action potentials at high frequency


Tetanus is a state of smooth and sustained contraction produced when motor neurons deliver a volley of action potentials


Types of Skeletal Muscle FibersSkeletal muscle fibers can be classifiedAs oxidative or glycolytic fibers, by the source of ATPAs fast-twitch or slow-twitch fibers, by the speed of muscle contraction


Oxidative and Glycolytic FibersOxidative fibers rely on aerobic respiration to generate ATPThese fibers have many mitochondria, a rich blood supply, and much myoglobinMyoglobin is a protein that binds oxygen more tightly than hemoglobin does


Glycolytic fibers use glycolysis as their primary source of ATPGlycolytic fibers have less myoglobin than oxidative fibers, and tire more easilyIn poultry and fish, light meat is composed of glycolytic fibers, while dark meat is composed of oxidative fibers


Fast-Twitch and Slow-Twitch FibersSlow-twitch fibers contract more slowly, but sustain longer contractionsAll slow twitch fibers are oxidativeFast-twitch fibers contract more rapidly, but sustain shorter contractionsFast-twitch fibers can be either glycolytic or oxidative


Most skeletal muscles contain both slow-twitch and fast-twitch muscles in varying ratios


Other 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 input


In 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 system


Concept 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 movement

Fig. 50-32GrasshopperHumanBiceps contractsTriceps contractsForearm extendsBiceps relaxesTriceps relaxesForearm flexesTibia flexesTibia extendsFlexor muscle relaxesFlexor muscle contractsExtensor muscle contractsExtensor muscle relaxes


Types of Skeletal SystemsThe three main types of skeletons are: Hydrostatic skeletons (lack hard parts)Exoskeletons (external hard parts)Endoskeletons (internal hard parts)


Hydrostatic 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 contractions

Fig. 50-33Circular muscle contractedCircular muscle relaxedLongitudinal muscle relaxed (extended)Longitudinal muscle contractedBristlesHead endHead endHead end


ExoskeletonsAn 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 cuticle


EndoskeletonsAn 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 movement

Fig. 50-34Examples of jointsHumerusBall-and-socket jointRadiusScapulaHead of humerusUlnaHinge jointUlnaPivot jointSkullShoulder girdleRibSternumClavicleScapulaVertebraHumerusPhalangesRadiusPelvic girdleUlnaCarpalsMetacarpalsFemurPatellaTibiaFibulaTarsals Metatarsals Phalanges112332

Fig. 50-34aExamples of jointsSkullShoulder girdleRibSternumClavicleScapulaVertebraHumerusPhalangesRadiusPelvic girdleUlnaCarpalsMetacarpalsFemurPatellaTibiaFibulaTarsals Metatarsals Phalanges123

Fig. 50-34bBall-and-socket jointScapulaHead of humerus1

Fig. 50-34cHinge jointUlnaHumerus2

Fig. 50-34dPivot jointUlnaRadius3


Size 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 scaling


The 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


Types of LocomotionMost animals are capable of locomotion, or active travel from place to placeIn locomotion, energy is expended to overcome friction and gravity


SwimmingIn water, friction is a bigger problem than gravityFast swimmers usually have a streamlined shape to minimize frictionAnimals swim in diverse waysPaddling with their legs as oarsJet propulsionUndulating their body and tail from side to side, or up and down


Locomotion on LandWalking, running, hopping, or crawling on land requires an animal to support itself and move against gravityDiverse adaptations for locomotion on land have evolved in vertebrates

Fig. 50-35


FlyingFlight requires that wings develop enough lift to overcome the downward force of gravityMany flying animals have adaptations that reduce body massFor example, birds lack teeth and a urinary bladder


Energy Costs of LocomotionThe energy cost of locomotion Depends on the mode of locomotion and the environmentCan be estimated by the rate of oxygen consumption or carbon dioxide production

Fig. 50-36


Animals specialized for swimming expend less energy per meter traveled than equivalently sized animals specialized for flying or running

Fig. 50-37Body mass (g)RunningSwimmingFlyingEnergy cost (cal/kgm)1021031011011031061RESULTS

Fig. 50-UN1StimulusSensory receptorStimulusAfferent neuronSensory receptor cellAfferent neuronTo CNSTo CNSNeuro- transmitterReceptor protein for neurotransmitter(a) Receptor is afferent neuron.(b) Receptor regulates afferent neuron.Stimulus leads to neurotransmitter release

Fig. 50-UN2Sensory receptorsMore receptors activatedLow frequency of action potentials(b) Multiple receptors activatedFewer receptors activated(a) Single sensory receptor activatedHigh frequency of action potentialsGentle pressureMore pressureMore pressureGentle pressureSensory receptor

Fig. 50-UN3FoveaPosition along retina (in degrees away from fovea)Optic diskNumber of photoreceptors904504590

Fig. 50-UN4


You should now be able to:Distinguish between the following pairs of terms: sensation and perception; sensory transduction and receptor potential; tastants and odorants; rod and cone cells; oxidative and glycolytic muscle fibers; slow-twitch and fast-twitch muscle fibers; endoskeleton and exoskeletonList the five categories of sensory receptors and explain the energy transduced by each type


Explain the role of mechanoreceptors in hearing and balanceGive the function of each structure using a diagram of the human earExplain the basis of the sensory discrimination of human smellIdentify and give the function of each structure using a diagram of the vertebrate eye


Identify the components of a skeletal muscle cell using a diagramExplain the sliding-filament model of muscle contractionExplain how a skeleton combines with an antagonistic muscle arrangement to provide a mechanism for movement

Figure 50.1 Can a moth evade a bat in the dark?Figure 50.2 A simple sensory pathway: Response of a crayfish stretch receptor to bendingFigure 50.3 Sensory receptors in human skin

Figure 50.4 Chemoreceptors in an insect

Figure 50.5 Specialized electromagnetic receptorsFigure 50.5a Specialized electromagnetic receptorsFigure 50.5b Specialized electromagnetic receptors

Figure 50.6 The statocyst of an invertebrateFigure 50.7 An insect earon its legFigure 50.8 The structure of the human earFigure 50.8 The structure of the human earFigure 50.8 The structure of the human earFigure 50.8 The structure of the human earFigure 50.8 The structure of the human earFigure 50.9 Sensory reception by hair cellsFigure 50.9 Sensory reception by hair cellsFigure 50.9 Sensory reception by hair cellsFigure 50.9 Sensory reception by hair cellsFigure 50.10 Transduction in the cochleaFigure 50.10a Transduction in the cochleaFigure 50.10b Transduction in the cochleaFigure 50.11 Organs of equilibrium in the inner earFigure 50.12 The lateral line system in a fishFigure 50.13 Sensory transduction by a sweet receptorFigure 50.14 How do mammals detect different tastes?

Figure 50.15 Smell in humansFigure 50.16 Ocelli and orientation behavior of a planarianFigure 50.17 Compound eyesFigure 50.17 Compound eyesFigure 50.17 Compound eyesFigure 50.18 Structure of the vertebrate eyeFigure 50.19 Focusing in the mammalian eyeFigure 50.20 Activation of rhodopsin by lightFigure 50.21 Receptor potential production in a rod cellFigure 50.22 Synaptic activity of rod cells in light and darkFigure 50.23 Cellular organization of the vertebrate retinaFigure 50.24 Neural pathways for visionFigure 50.25 The structure of skeletal muscle

Figure 50.25 The structure of skeletal muscle

Figure 50.25 The structure of skeletal muscle

Figure 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.

Figure 50.27 Myosin-actin interactions underlying muscle fiber contractionFor the Cell Biology Video Myosin-Actin Interaction, go to Animation and Video Files.

Figure 50.27 Myosin-actin interactions underlying muscle fiber contraction



Figure 50.28 The role of regulatory proteins and calcium in muscle fiber contractionFigure 50.29 The regulation of skeletal muscle contractionFigure 50.29a The regulation of skeletal muscle contractionFigure 50.29b The regulation of skeletal muscle contractionFigure 50.30 Motor units in a vertebrate skeletal muscleFigure 50.31 Summation of twitchesFigure 50.32 The interaction of muscles and skeletons in movementFor the Discovery Video Muscles and Bones, go to Animation and Video Files.

Figure 50.33 Crawling by peristalsisFigure 50.34 Bones and joints of the human skeletonFigure 50.34 Bones and joints of the human skeletonFigure 50.34 Bones and joints of the human skeletonFigure 50.34 Bones and joints of the human skeletonFigure 50.34 Bones and joints of the human skeletonFigure 50.35 Energy-efficient locomotion on landFigure 50.36 Measuring energy usage during flightFigure 50.37 What are the energy costs of locomotion?

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