Chapter 12: MuscleMuscle TerminologyMuscleSkeletal MuscleFlexion vs. ExtensionSlide 6PowerPoint PresentationThick FilamentsThin FilamentsActin-Myosin CrossbridgesSlide 11Muscle ContractionThe SarcomereRelaxed StateContractionEnergyFast-Twitch and Slow-Twitch Muscle FibersLength-TensionSlide 19Contraction ForceMechanics of Body MovementSmooth Muscle ClassificationPhasic vs. TonicSingle UnitMulti-UnitSmooth MuscleSlide 27Slide 28Slide 29Slide 30RelaxationSarcoplasmic Calcium ReleaseSlide 33Smooth Muscle RegulationCardiac MuscleSlide 36Chapter 12: Muscle•Skeletal muscle•Mechanics of body movement•Smooth muscle•Cardiac muscle© 2013 Pearson Education, Inc.Muscle TerminologyMuscleNucleusMuscle fiber(cell)StriationsSkeletal muscle fibers are large,multinucleate cells that appearstriped or striated under themicroscope.NucleusMuscle fiberIntercalateddiskStriationsCardiac muscle fibers are alsostriated but they are smaller,branched, and uninucleate. Cellsare joined in series by junctionscalled intercalated disks.NucleusMuscle fiberSmooth muscle fibers are smalland lack striations.Skeletal Muscle•Usually attached to bones by tendons•Flexor: brings bones together•Extensor: moves bones away© 2013 Pearson Education, Inc.Flexion vs. ExtensionTricepsmusclerelaxes.Biceps musclecontracts (flexor).Flexion moves bonescloser together.Bicepsmusclerelaxes.Triceps musclecontracts (extensor).Extension moves bonesaway from each other.Skeletal MuscleANATOMY SUMMARYMitochondriaThickfilamentThinfilamentMyofibrilSarcolemmaT-tubulesNucleusSarcoplasmicreticulumT-TUBULEST-tubules are extensions of the cell membrane (sarcolemma)that associate with the ends (terminal cisternae) of thesarcoplasmic reticulum.TriadThickfilamentSarcolemmaThinfilamentTerminalcisternaT-tubule brings actionpotentials into interiorof muscle fiber.Sarcoplasmicreticulum stores Ca2.Thick FilamentsANATOMY SUMMARYHingeregionM lineThick filamentsMyosin tailMyosin headsMyosin moleculeThin FilamentsANATOMY SUMMARYThin filamentsTitinTropomyosin G-actin moleculeNebulinTroponinActin chainNebulin aligns actinActin-Myosin CrossbridgesANATOMY SUMMARYZ diskZ diskM lineTitinMyosincrossbridgesTitin provides elasticity and stabilizes myosinOrganization of a SarcomereThe Z disk (notshown in part (c))has accessoryproteins that linkthe thin filamentstogether, similar tothe accessoryproteins shown forthe M line. Myosinheads are omittedfor simplicity.KEYActinMyosinI bandActin onlyH zoneMyosin onlyM lineMyosin linkedwith accessoryproteinsA band(outer edge)Actin and myosinoverlapI band H zoneA bandI bandSarcomereZ diskM lineZ diskMuscle Contraction•Muscle tension: force created by muscle•Load: weight or force opposing contraction•Contraction: creation of tension in muscle•Relaxation: release of tension© 2013 Pearson Education, Inc.The SarcomereMuscle RelaxedMuscle ContractedH zone and I band bothshorten, while A bandremains constantSarcomereshortens withcontraction.Half ofI bandHalf ofI bandH zoneI bandA bandMyosinActinZ lineIIHThe Sarcomere Shortens During Contraction. As contraction takesplace, actin and myosin do not change length but instead slide past one another.Relaxed StateTropomyosinPiADPMyosin headTNTroponin G-actinRelaxed state. Myosin head cocked. Tropomyosinpartially blocks binding site on actin. Myosin isweakly bound to actin.ContractionInitiation of contraction. A calcium signalinitiates contraction.PiADPCytosolic Ca2TNPower strokeActinmovesTropomyosin shifts,exposing bindingsite on actin.Actin filamentmoves.Myosin binds stronglyto actin and completespower stroke.Ca2 levels increasein cytosol.Ca2 binds totroponin (TN).Troponin-Ca2 complex pullstropomyosinaway from actin’smyosin-binding site.EnergyPhosphocreatineResting muscle stores energy from ATP in the high-energy bonds ofphosphocreatine. Working muscle then uses that stored energy.Muscle at restWorking muscleATP from metabolism  creatineADP  phosphocreatinecreatinekinasecreatinekinasePhosphocreatine  ADPCreatine  ATPneeded for• Myosin ATPase (contraction)• Ca2-ATPase (relaxation)• Na-K-ATPase (restores ions that cross cell membrane during action potential to their original compartments)Fast-Twitch and Slow-Twitch Muscle Fibers•Slow-twitch fibers–Rely primarily on oxidative phosphorylation•Fast-twitch fibers–Develop tension faster –Split ATP more rapidly–Pump Ca2+ into sarcoplasmic reticulum more rapidly–Fast-twitch glycolytic fibers–Rely primarily on anaerobic glycolysis–Fast-twitch oxidative-glycolytic fiber–Use oxidative and glycolytic metabolism© 2013 Pearson Education, Inc.Length-TensionLENGTH-TENSION RELATIONSHIPSToo much or too little overlap of thick and thin filaments in resting muscle results in decreased tension.Optimalresting lengthIncreasedlengthDecreasedlengthTension (percent of maximum)ABCDE1008060402001.3  m 2.0  m2.3  m3.7  mMOTOR UNITSKEYMotor unit 1Motor unit 2Motor unit 3SPINAL CORDOne muscle may havemany motor units ofdifferent fiber types.Neuron 1Neuron 2Neuron 3MotornerveMusclefibersA motor unit consists of one motor neuron and all the muscle fibers itinnervates. A muscle may have many motor units of different types.Contraction Force•Recruitment of additional motor units by the nervous system increases contraction force•Asynchronous recruitment of motor units helps avoid fatigue–Different motor units take turns maintaining tension© 2013 Pearson Education, Inc.Mechanics of Body Movement•Isotonic contractions create force and move a load–Concentric action is a shortening action–Eccentric action is a lengthening action•Isometric contractions create force without moving a load–Series elastic elements–Sarcomeres shorten while elastic elements stretch, resulting in little change in overall length© 2013 Pearson Education, Inc.Smooth Muscle Classification•By location–Vascular, gastrointestinal, urinary, respiratory, reproductive, ocular•By contraction pattern–Phasic smooth muscles–Tonic smooth muscles•By communication with neighboring cells–Single-unit smooth muscle, or visceral smooth muscle–Multi-unit smooth muscle© 2013 Pearson Education, Inc.Phasic vs. TonicSMOOTH MUSCLE CONTRACTIONSTimeContraction forceTimeContraction forceTimeContraction forceTimeContraction forceA phasic smooth muscle that is usually relaxed.Example: esophagusA phasic smooth muscle that cycles between contraction andrelaxation. Example: intestineA tonic smooth