13 Phys Muscle Physiology...Muscle Physiology •2 distinct events happen which lead to muscle...
Transcript of 13 Phys Muscle Physiology...Muscle Physiology •2 distinct events happen which lead to muscle...
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MusclePhysiology
PhysiologyUnit2
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InPhysiologyToday
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SkeletalMuscle
• Characteristics– Striated–Multinucleated–Voluntary
• Organization–Myofiber• Myofibril–Myofilament
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Sarcomere
• Functionalunitofskeletalmuscle
• Composedof3filaments– Thickfilament
• Myosin
– Thinfilament• Actin• Troponin• Tropomyosin
– Elasticfilament• Titin
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ThickandThinFilaments
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SlidingFilamentTheoryofContraction
• Crossbridgesformbetweenthethickandthinfilaments
• Thinfilamentsslideacrossthethickfilaments– Thinfilamentswillmove
closertogether– DistancebetweenZlines
decreases– IbandandHbandsshorten
duringcontraction– Abandstaysthesame
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MusclePhysiology
• 2distincteventshappenwhichleadtomusclecontraction
1.Electricalevents– ActionPotential– Receptoractivation– EPP– AP– Electricaleventstriggerthemechanicalevents
2.Mechanicalevents– Developingtensioninthemuscle– IncreaseCa2+ levels– contractileproteinsmoving– musclefibershortens
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StimulustoContraction• Stimulus
– Receptoractivation– Skeletalmuscle:AChbindingtoN-Achr– ResultsinanEPP
• Latentperiod– Excitation-Contractioncoupling
• Contractionperiod– Cross-BridgeCycling– Generatestensioninthemuscle
• Relaxationperiod– Stimulusendsorcellfatigues– Musclereturnstoitsrestingstate
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MuscleTwitch
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Stimulus
• Somaticmotorneuronsinnervateskeletalmuscle• Largestdiameterneurons• Myelinated• HighvelocityAP
• Uponreachingmuscle,axondividesintomanybranches
• Eachbranchformingasinglejunctionwithamusclefiber=motorunit
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EPPtoAP
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ActionPotentialtoContraction• APlasts1-2ms• Completedbeforeany
mechanicalactivitybegins• Mechanicalactivity
(contraction)maylast>100ms
• Electricalactivity(actionpotential)doesnotactoncontractileproteins
• Producesastateofincreasedcytolsolic[Ca2+]– Resting[Ca2+]=0.1mMol/L– AfterAP[Ca2+]=1mMol/L
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LatentPeriod
• Excitation-ContractionCoupling• SequenceofeventsfromthegenerationofanAPacrossthesarcolemmatoCa2+ releaseinsideofthemyofiber
• Sarcolemmaisanexcitablemembrane– GeneratinganAP(fromEPP)– PropagatinganAP– Similarmechanismsasneurons
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ContractionPeriod
• IncreaseinintracellularCa2+ levelstriggerthemechanicalevents
• Ca2+ activatesCross-BridgeCycling
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SarcoplasmicReticulum• LateralsacsstoreCa2+
• T-tubulehasDHPreceptors– DHPreceptorsarenormally
voltagegatedCa2+channels– Inskeletalmusclet-tubules,
actsasavoltagesensor
• SRhasryanodinereceptors– IntracellularCa2+channels
– WhenCa2+channelsopen,Ca2+ movesintocytoplasm
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CalciumRelease
• DHPreceptorstriggercalciumrelease
• Ryanodinecalciumchannelsopen
• InfluxofcalciumfromSRintocytoplasm
• Calciuminfluxtriggerscrossbridgecycling
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ActivationbyCa2+• Tropomyosincoversthe
myosinbindingsitesonactin• Troponinholdstropomyosin
inplace- has3sub-units1. TroponinI
• inhibitory2. TroponinT
• Tropomyosinbinding3. TroponinC
• Calciumbinding
• IncreaseinintracellularCa2+levelscauseTroponinCtobindtoCa2+ whichexposesbindingsitesonactin
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Troponin
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CrossBridgeCycling
1. Attachmentofthemyosincross-bridgetoactinofathinfilament
2. Movementofthecross-bridge,pullingonthethinfilament– Eachcross-bridgemovesindependentlyofallothercross-
bridges– Asynchronouspullingaction
3. Detachmentofcross-bridgefromthethinfilament4. Energizingthecross-bridgesoitcanagainattachto
athinfilamentandrepeatthecycle
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Cross-BridgeCycling
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ATPinMuscleMetabolismUsesofATPinMuscle
Contraction
• Activationofmyosin– High-energymyosin
• Releaseofmyosinheadfromactinmolecule
• ActivetransportofCa2+intoSRfromthesarcoplasm
MuscleContractionRequiresALotofATP!
• NoATP“storage”• 3pathwaysforregeneration– Phosphagensystem– Glycolysis– Aerobicrespiration
EnergyATP+H20 à ADP+pi +H+ +
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SourcesofATP
1.Phosphagen System2.Glycolysis3.Oxidativephosphorylation
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PhosphagenSystem• Creatine
– Naturalproducednythebody– Madefromaminoacids
• CreatinePhosphate– Astoreofhighenergy
phosphate
• CreatineKinase– Transfersphosphategroup
fromCPtoADP– Presentat3xhigher
concentrationinskeletalmuscle CrP+ADP+H+---->Cr+ATP
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PhosphagenSystem
• AdenylateKinase– AwaytoquicklymakeATP– ADP+ADP---- >ATP+AMP
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AerobicRespiration
• PrimarysourceofATPproductionformuscleduringrestorlightexercise
• Fuelutilizationbyskeletalmuscle– fattyacids– muscleglycogen– bloodborneglucose
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AnaerobicMechanisms• Oxygenconsumption– ExercisingmusclecanconsumemoreATPthancanbeproducedbyaerobicrespiration
– Musclecellswillutilizeavailableglucoseandglycogenreserves
– Glycolysis willthenproduceATPtokeepupwiththedemandoftheactivemuscle• Lacticacidaccumulates
– OxygenDebt• Theamountofoxygenconsumedtogetthemusclecellsandplasmabacktonormalconditions– Glucoselevels– Glycogenreserves– Convertinglacticacidbacktopyruvic acid
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SmoothMuscle• singlecells,nostriations• circularlayer
arrangement• nosarcomeresor
troponin• actin:myosinratio=13:1• utilizesCa2+/calmodulin
mechanism• gradeddepolarizations• singleunitvsmulti-unit• autonomicinnervation
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SmoothMuscle