LE 49-20OutersegmentDisksRodInsideof diskCell bodySynapticterminalRhodopsinCytosolRetinalOpsintrans isomerLight Enzymescis isomerLE 49-21LightINSIDE OF DISKCYTOSOLPDETransducinInactiverhodopsinDiskmembraneActiverhodopsinPlasmamembranecGMPNa+GMPNa+Membranepotential (mV)EXTRACELLULARFLUIDLightHyper-polarizationTime–70Dark0–40LE 49-22Light ResponsesRhodopsin activeNa+ channels closedRod hyperpolarizedBipolar cell eitherhyperpolarized ordepolarized, depending on glutamate receptorsNo glutamatereleasedDark ResponsesRhodopsin inactiveNa+ channels openRod depolarizedBipolar cell eitherdepolarized orhyperpolarized, depending on glutamate receptorsGlutamatereleasedLE 49-23RetinaOptic nerveTobrainConePhotoreceptorsRetinaRodNeuronsPigmentedepitheliumBipolarcellAmacrinecellHorizontalcellOpticnervefibersGanglioncellInformation carried by the optic nerve is perceived as"sight," whereas information carried by the auditorynerve is perceived as "sound." Which of the followingstatements best explains this?– A. The information is carried to different areas of the brain.– B. The structure of neurons in the optic nerve differs from thatin the auditory nerve.– C. Light energy and sound waves are different from each other.– D. Different ions enter and leave the axons of the two differentnerves.– E. Action potentials that carry visual information are of adifferent amplitude and frequency than those carrying soundinformation.LE 49-24LeftvisualfieldRightvisualfieldLefteyeRighteyePrimaryvisual cortexLateralgeniculatenucleusOptic nerveOptic chiasmLE 49-27BicepscontractsHumanTricepsrelaxesForearmflexesBicepsrelaxesTricepscontractsForearmextendsExtensormusclerelaxesFlexormusclecontractsGrasshopperExtensormusclecontractsFlexormusclerelaxesTibiaextendsTibiaflexesLE 49-28Bundle ofmuscle fibersSingle muscle fiber(cell)Plasma membraneNucleiMuscleMyofibrilDark bandSarcomereZ lineLightbandI bandTEMA band I band0.5 µmM lineThick filaments(myosin)SarcomereH zoneZ lineThin filaments(actin)Z lineLE 49-29Sarcomere0.5 µmZHARelaxed muscle fiberIContracting muscle fiberFully contracted muscle fiberLE 49-30–4Thin filamentsThick filamentThin filamentThick filamentMyosin head (low-energyconfiguration)Cross-bridgebinding siteMyosin head (high-energy configuration)ActinCross-bridgeMyosin head (low-energy configuration)Thin filament movestoward center of sacomere.LE 49-31Myosin-binding sites blocked.Myosin-binding sites exposed.TropomyosinCa2+-binding sitesActin Troponin complexMyosin-binding siteCa2+• For a muscle fiber to contract, myosin-binding sites must be uncovered• This occurs when calcium ions (Ca2+)bind to a set of regulatory proteins, thetroponin complex• The stimulus leading to contraction of amuscle fiber is an action potential in a motorneuron that makes a synapse with the musclefiberLE 49-32Ca2+ releasedfrom sarcoplasmicreticulumMitochondrionMotorneuron axonSynapticterminalT tubuleSarcoplasmicreticulumMyofibrilPlasma membraneof muscle fiberSarcomere• The synaptic terminal of the motorneuron releases the neurotransmitteracetylcholine• Acetylcholine depolarizes the muscle,causing it to produce an action potential• Action potentials travel to the interior of the musclefiber along transverse (T) tubules• The action potential along T tubules causes thesarcoplasmic reticulum to release Ca2+• The Ca2+ binds to the troponin-tropomyosincomplex on the thin filaments• This binding exposes myosin-binding sites andallows the cross-bridge cycle to proceedLE 49-33Ca2+CYTOSOLCa2+SRPLASMAMEMBRANET TUBULESynaptic cleftSynaptic terminalof motor neuronAChNeural Control of MuscleTension• Contraction of a whole muscle is graded,which means that the extent and strength ofits contraction can be voluntarily altered• There are two basic mechanisms by whichthe nervous system produces gradedcontractions:– Varying the number of fibers that contract– Varying the rate at which fibers are stimulated• In a vertebrate skeletal muscle, eachbranched muscle fiber is innervated byone motor neuron• Each motor neuron may synapse withmultiple muscle fibersLE 49-34Motorunit 1Motorunit 2NerveSynaptic terminalsMotor neuroncell bodySpinal cordMotor neuronaxonMuscleTendonMuscle fibers• A motor unit consists of a single motorneuron and all the muscle fibers it controls• Recruitment of multiple motor neuronsresults in stronger contractions• A twitch results from a single actionpotential in a motor neuron• More rapidly delivered action potentialsproduce a graded contraction by summationLE 49-35TetanusSummation oftwo twitchesSingletwitchTensionActionpotentialPair ofactionpotentialsTimeSeries of actionpotentials athigh frequency• Tetanus is a state of smooth and sustainedcontraction produced when motor neuronsdeliver a volley of action potentialsTypes of Muscle Fibers• Skeletal muscle fibers are classified as slowoxidative, fast oxidative, and fast glycolytic• These categories are based on theircontraction speed and major pathway forproducing
View Full Document
Unlocking...