Muscle Energetics and MechanicsCyclic ContractionsCyclic ContractionsExperimentalsetupWork Loops - positive net work exampleWork Loops - positive net work exampleCyclic ContractionsWork Loop ExamplesLecture 14, 14 Oct 2003Chapter 10, MusclesChapter 11, Movement and BehaviorVertebrate PhysiologyECOL 437University of ArizonaFall 2003instr: Kevin Boninet.a.: Bret PaschVertebrate Physiology 4371. Muscles (Ch10)2. Announcements old exam, review sheet exam next Tuesday papers due today mid-semester evaluations seminars etc.3. Behavior and Movement (CH11)UA UndergradConservationBiology InternshipsRandi B. Weinstein, Ph.D.Department of PhysiologyUniversity of [email protected] Energetics and MechanicsCyclic ContractionsIn cyclic motions muscle contractions are not purely isometric or isotonic.Instead, muscles shorten and lengthenduring each cycle.How much work does a muscle do duringone cycle?Cyclic ContractionsExample: repeatedly lifting load-biceps develops more tension as it shortens than when it lengthens-biceps does net positive workFlex-biceps shortensExtend -biceps lengthensFlexor vs ExtensorExperimentalsetupMuscle lever controlsmuscle length andmeasures forceElectrical stimulationpattern synchronizedwith muscle length(rate ~EMG data)Muscle is movedalong its linear axisservomotorWork Loops - positive net work exampleLengthForceStimulationTime0.2 mm20 mNlengthenshortenshortening (contraction)Josephson, 1985 (insect flight muscle)25 cycles/sSee textFig. 10-38Work Loops - positive net work exampleForceLengthForce0.2 mm20 mNWork outputduring shorteningLength20 mN0.2 mmWork Loops - positive net work exampleLengthForceStimulationTime0.2 mm20 mNlengthenshortenlengthening (relaxation)25/sWork Loops - positive net work exampleForceWork outputduring shorteningLength20 mNLengthForce0.2 mm20 mNLengthWork inputto lengthen0.2 mmWork Loops - positive net work exampleForceWork outputduring shorteningLength20 mNLengthForce0.2 mm20 mNLengthWork inputto lengthen0.2 mmNet workper cycleLengthWork Loops - positive net work exampleForce20 mNLengthForce0.2 mm20 mN0.2 mmNet workper cycleLengthStimulation25 cycles/s(0.04 s/cycle)= 4.5 µNm 4.5 µNm0.04 sNet power =Net work/cycleCycle duration== 113 µNm/sMuscle generates power!Cyclic ContractionsFlexExtendExample: repeatedly lowering load-biceps develops more tension as it lengthens than when it shortens-biceps does net negative workWork Loop - negative net work exampleForceLengthForce0.2 mm20 mNStimulationWork outputduring shorteningLengthLengthWork inputto lengthenNet workper cycleLength25/s-4.5 µNmphaseshiftMuscle absorbs energy!Work Loop ExamplesDickinson et al., 2000Cardiac Muscle (the other striated muscle)-Small muscle fiber cells with only one nucleus-Individual fibers are connected to neighborselectronically via gap junctions-Two types of fibers:1. Contractile (similar to skeletal muscle)2. Conducting (including pacemaker cells)Do not contract, but transmit electrical signal-Cardiac contraction myogenic (arises within heart)Can be influenced by autonomic nervous system(alpha, beta adrenoreceptors increase [Ca2+])-Long-lasting AP with long plateau phase, and long refractory period - why?Skeletal muscleCardiac muscleFig. 10-49Randall et al. 2002Fig. 10-18Randall et al. 2002Cardiac Muscle (the other striated muscle)-Intracellular calcium from SR and across plasmamembrane (unlike in skeletal)-Dihydropyridine receptors in T-tubules arevoltage-activated calcium channels-Ryanodine receptors then release more calcium from SRinto the cytoplasm (calcium-induced calcium release)-During relaxation, Calcium pumped actively backinto SR and out across plasma membraneSmooth Muscle-Lacks sarcomeres, isn’t striated-Walls of hollow organs – visceral functions(GI tract, urinary bladder, uterus, blood vessels)-Heterogenous-Innervated by autonomic NS-Each fiber is individual cell with one nucleus-No T-tubules-Organized into bundles of actin and myosin anchored todense bodies or to the plasma membrane-Can be single-unit or multi-unit-Myogenic and electronically linked via gap junctions(peristaltic waves in GI tract)Neurogenic (walls ofblood vessels, iris)Smooth Muscle-Autonomic NT released from varicosities alongaxon, not at motor endplate, affecting many cells-Poorly developed SR, calcium mostly across plasmamembrane-Some smooth muscle responds to stretch (vessels, GI)-Several ways to regulate calcium concentration (no troponin)-One is via calcium-calmodulincomplex that then binds tocaldesmon, removing caldesmon fromblocking actin binding sites-Processes all very slow and require little energy-Latch stateprolonged contraction, low energy use (0.3% striated)Smooth MuscleLow rate ofcross-bridgecyclingMechanismnot well-understoodFig. 10-53Randall et al. 2002--Uta stansburianaSceloporus magisterSceloporus undulatusSceloporus virgatusUma notataCallisaurus draconoidesCophosaurus texanusHolbrookia maculataPhrynosoma cornutumPhrynosoma modestumPhrynosoma mcalliiSceloporusGroupSandHorned11 Species of PhrynosomatidaeHigh-Speed TreadmillTwitch Speed (SPRINTING) SO = Slow OxidativeFOG = Fast-Oxidative GlycolyticMuscle Fiber-Type CompositionFG = Fast GlycolyticFOG = Fast-Oxidative GlycolyticOxidative Capacity (ENDURANCE)Iliofibularis muscleIliofibularis Muscle (IF)cross-section with darker oxidative core that appears red in fresh tissueDorsal view oflizard hindlimb IFHistochemistryFemurCross Sectionof Hindlimb atMid-ThighHistochemistry IFIliofibularis Muscle (IF)SuccinicDehydrogenase(SDH)HistochemistryMyosin ATPasemATPase(fast-twitch)SDH(oxidative)SO(slow-oxidative;light mATPase,dark SDH)FG(fast-twitchglycolytic; darkmATPase, light SDH)FOG(fast-twitchoxidativeglycolytic; darkmATPase anddark SDH)HistochemistrySerial sections stained for:Proportional area of all three fibertypes sums to 1.FG + FOG + SO = 1--Uta stansburianaSceloporus magisterSceloporus undulatusSceloporus virgatusUma notataCallisaurus draconoidesCophosaurus texanusHolbrookia maculataPhrynosoma cornutumPhrynosoma modestumPhrynosoma mcalliiSceloporusGroupSandHorned11 Species of PhrynosomatidaeWhat are the Potential Sourcesof Muscle Variation?1. Whole-leg muscle area2. Proportion of a muscle in the thigh3. Change in size of individual fibers4. Variation in fiber-type composition1. Whole-leg muscle area2. Proportion of a muscle in the thigh3. Change in size of individual fibers4. Variation in fiber-type compositionFocus on the Iliofibularis muscleWhich Muscle
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