muscle structure 11

8/7/2019 Muscle Structure 11

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MUSCLEPHYSIOLOGY

PamelaRBosch,PhD,PT

PT531,AppliedPhysiologyArizonaSchoolofHealthSciences,A.T.SJllUniversity

ThecopyrightedmaterialsavailableinthisclassareforeducaJonaluseonly.

OnecopyperstudentispermiNedforeducaJonalpurposes.RedistribuJonof

copyrightedmaterialisnotpermiNed.


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References

Lieber,RL.2002.SkeletalMuscleStructure,FuncJon,andPlasJcity.2 nded.Lippinco'Williams&Wilkins,Philadelphia.

McComasA.1996.SkeletalMuscle:FormandFuncJon. HumanKine8cs,Champaign,IL

SherwoodL.2010.HumanPhysiology:FromCellstoSystems.7 thed.Thomson,Belmont,CA.


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ObjecJves

1. MakegeneraldisJncJonsbetweensmoothandskeletalmuscle2. DescribetheorganizaJonandstructureofskeletalmuscle,includingmyofilaments,the

sarcomere,t-tubules,thesarcoplasmicreJculum,andconnecJveJssuemembranes,andtheir

funcJons

3. DescribestructuralchangesthatoccurinmuscleanditssurroundingconnecJveJssueasaresultofimmobilizaJoninashortenedandinalengthenedposiJon

4. DifferenJateamongthetypesofmusclefiber5. UnderstandthatATPhasvariousfuncJonsinthebody6. Describethe3sourcesofATPproducJoninskeletalmuscle,anddifferenJateamongtheirroles.7. UnderstandtherelaJvedifferencesinquanJtyofATPproducJonamongthedifferentmethodsof

producingATPinskeletalmuscle

8. StatethedifferencebetweentheKrebsCycleandBetaOxidaJon9. UnderstandtheconceptsofskeletalmuscleexcitaJon-contracJoncoupling10. DescribetheorganizaJonandinnervaJonofmotorunitsandthevariousmotorunittypes11. DescribethedifferencesbetweentwitchandtetaniccontracJonsandtheeffectofasynchronous

acJvaJonofmotorunits

12. Describefeaturesofthelength-tensionandforce-velocityrelaJonofskeletalmuscle13. Describedifferencesbetweenisometric,concentricandeccentriccontracJons14. Describethechangesthatoccurinmuscleasaresultofenduranceandstrengthtraining15. IdenJfyanddifferenJateamongdiseasesaffecJngthemuscleorneuromuscularsystem16. IdenJfytheeffectsofagingonskeletalmuscle


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Fig. 8-1, p. 254


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SmoothMuscleConsJtutesthewallsofholloworgans

FibersaresmallerInbothdiameterandlength(donotextendthe

lengthofthemuscle)

FineconnecJveJssuebetweenfibersSinglenucleuspercell


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SmoothMuscle Organizedinsheets

LongitudinallayerparalleltoorganslongaxisCircumferenJallayeraroundtheorgan

WhatisthefuncJonalsignificanceofsuchorganizaJon?


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Peristalsis


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SmoothMuscleInnerva2on

Autonomicnervoussystem(involuntary) Neurotransmi'erreleasedfrom

swellingsatnerveendandalongaxon Acetylcholine,norepinephrine

Musclecanalsobes8mulatedbysomecircula8nghormonesor

drugs EX:circula8ngacetylcholinecauses

relaxa8onofarterialsmoothmuscle

EX:circula8ngadenosinecausesrelaxa8onofarterialsmoothmuscleinexercisingmuscle

SkeletalMuscleInnerva2on

SomaJc(voluntary)nervoussystem

HighlystructuredneuromuscularjuncJon


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GapjuncJonsallowtransmissionofacJon

potenJalsfromcelltocellinsmoothmuscle.

Skeletalmusclecellsareelectrically

isolatedfromeach

other

GapjuncJonsalso:

1. AllowcommunicaJonbetweencells,and2. Providemechanicallinkagebetweencells.


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Afinalcomparisonbetweensmooth

andskeletalmuscle:

Hyperplasiav.Hypertrophy

Hyperplasia,anincreaseincellnumber,isnormalinsmoothmuscle.

Hypertrophy,anincreaseincellsize,isnormalinskeletalmuscle.

BenignProsta2cHypertrophy


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SmoothMuscleGrowth

Hyperplasia

Increaseincellnumber Occursduringperiodsof

humangrowthand

development

Hypertrophy

Increaseincellsize Isusuallypathological

EX:Inhypertension,arterialsmoothmusclehypertrophies

Bladdermusclehypertrophy,withprostateenlargement

Couldsmoothmusclehypertrophyeverbe

normal?


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SkeletalMuscle


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SkeletalMuscleFuncJons

Movement Posture ointstability HeatgeneraJon


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Eachskeletalmuscleisadiscreteorgan.

MuscleFascicleFiber

Hundredstothousandsoffibers(cells)compriseonemuscle.


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Fig. 8-2, p. 255

FIBER

MYOFIBRIL

(sarcomeres)

MYOFILAMET

(acJnandmyosin)


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actin! troponin!tropomyosin!

thick filament!

thin filament! cross bridge!myosin!

Z disk!

Sarcomere!


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OtherJssueinSkeletalMuscle

ervesBloodvesselsConnecJveTissue:

Epimysiumsurroundsmuscle

Perimysiumsurroundsfascicles;

providespathfornervesandvessels

throughmusclebelly

Endomysiumsurroundseachmuscle

fiber


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FuncJonsofMuscleConnecJveTissue

Scaffoldingindevelopment Conduitfornervesandvessels Resistanceofpassivestretching Maintenanceofshape TransmissionofcontracJleforcestotendon


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Proposedeffectsofbrief,passivestretching(Magnusson,1998)

Aimofstretchingisinhibi2onofreflexac2vityinmuscle,which Reducesresistancetostretch IncreasesjointrangeofmoJon

OtherpotenJalmechanismsforeffecJvenessofstretching:

Amplifiedstretchtolerance

AlteraJonsinmechanicalproperJesofmuscleScanJMedSciSports;:65-77.


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ConnecJveJssuecontributestomuscle-tendon

elasJcity(Magnusson,1998)

ParallelelasJccomponentperimysiumprovidesevendistribuJonofstressandpreventsoverstretching

SerieselasJccomponentendomysiumtransfersforcefromcontracJlecomponentstotendonandboneinseries

Passivestretchwithinaphysiologicrangeresultsin2%strainoftendon,8%strainofmuscle-tendonjuncJon


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Contractile

component(sarcomeres)

Series-elasticcomponent

(connective

tissue/tendon)

Load

Load Fig. 8-18, p. 269


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BandyWDandIrionM.1994.TheeffectofJmeonstaJcstretchon

theflexibilityofthehamstringmuscles.PhysicalTherapy;74:845-852.

Comparedtheeffectofa15,30,or60secondholdduring

stretching5d/wkovera6-weekperiod.

Both30and60sholdsweremoreeffecJvethan15s,but30s

wasaseffec2veas60sin

increasingflexibility


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BandyWD,IrionM,BrigglerM.1998.TheeffectofstaJcstretchand

dynamicrangeofmoJontrainingontheflexibilityofthehamstringmuscles.

JOSPT;27;295-300.

Asingle,30sstretchwasmoreeffec2vefor

increasingflexibilitythan

dynamicrangeofmoJon.


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MagnussonSP,AagaardP,ielson.2000.Passiveenergyreturnaer

repeatedstretchesofthehamstringmuscle-tendonunit.Medicineand

ScienceinSports&Exercise;32:1160-1164.

3repeated,45-sstretchesproducednoshorttermeffectonviscoelasJcproperJesinskeletalmuscle. Thatis,therewerenochangestophysicalproperJesof

muscle(sJffness)aer3stretches.

Therewasadeclineinresistancetostretchwithina45-sbout Butnodifferenceinresistancefrom1 stto3rdstretch

Thesubjectstolerancetostretchingdidimprove.


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Whataretheeffectsofprolonged

staJcstretchingonmuscleandconnecJveJssue?


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WilliamsPE,andGoldspinkG.1978.Changesinsarcomere

lengthandphysiologicalproperJesinimmobilizedmuscle.J

Anat;127:459-468

ResearchQuesJons:TowhatextentarealteraJonsinsarcomere

numberduringimmobilizaJonaccompaniedby

changesinsarcomerelength?

Ismaximumtensionabletobedevelopedbyanimmobilizedmuscle?


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Anat;127:459-468

Methods:

Hindlimb(soleus)immobilizaJonofonelimbin1wkoldand8wkoldmice

Muscleimmobilizedfor3weeksineither: Shortened LengthenedposiJon

Musclescountedforsarcomerelength/number,orlength/tensionmeasurementstaken


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Anat;127:459-468

Resultsregardingsarcomerelength/number:

MuscleimmobilizedinashortenedposiJonhadareduc2oninsarcomerenumber,butanINCREASEin

sarcomerelength(andshortlength/tensioncurves)

MuscleimmobilizedinalengthenedposiJonexperiencedanINCREASEinnumberofsarcomere,butareduc2oninsarcomerelength


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Anat;127:459-468

Resultsregardinglength/tensionrelaJonship:

Shortenedmusclesweighedtheweightofcontrolmuscles,andhadsignificantlyreducedtension

generaJoncapacity

Length-tensioncurveswereveryshortMuscleimmobilizedinalengthenedposiJonvaried,butwerealwayshigherthancontrolsintheability

togeneratetension


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Anat;127:459-468

Resultsregardingyoung(1wkold)vadult(8wkold)mice: Shortenedmusclesweresimilarbetweenyoungandadult

ReducJoninsarcomerenumber,increaseinlengthofsarcomeres MuscleimmobilizedinalengthenedposiJonhadareducJonin

sarcomerenumber(thisisdifferentfromadults),butsarcomerelengthwasalsoreducedcomparedtocontrols Youngmayexperienceincreasedtendonlength,orincreasedstaggeringof

musclefibers

Youngexperiencedreducedmusclelengthcomparedtocontrols,regardlessofimmobilizaJoninshortenedorlengthenedposiJons. ?IncreasedtendonlengthorreduceddistancefromorigintoinserJonasaresult

ofbonegrowth Length/tensioncurvesrespondedsimilarlytoadultsforeachcondiJon


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Anat;127:459-468

Discussion:MuscleJssueisveryadaptable!Sarcomerenumberisnotfixed.Sarcomeresadjusttodevelopmaximaltension

whenmuscleisimmobilized.


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WilliamsPEandGoldspinkG.1984.ConnecJveJssue

changesinimmobilizedmuscle.JAnat;138:343-350.

LossofsarcomeresandreducJoninmusclefiberlengthasaresultofimmobilizaJoninashortenedposiJonareassociatedwithincreasedresistancetopassivestretch.

ForcespassivelyimposedonthemusclebystretcharedistributedviaconnecJveJssueframework. Theamount/arrangementofconnecJveJssueinthe

perimysiumandendomysiumwouldbeexpectedtoaffectmuscleelasJcity.

ResearchQuesJon:IsincreasedsJffnessofimmobilizedmuscleaccountedforbyincreasedcollagencontent,andifso,wheredoesitoccur?WhatistheJmecourseforchange?


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8weekoldmicehadahindlimbimmobilizedashortenedposiJon. Musclesmeasuredat1day-to4-weekintervals SomelimbswereimmobilizedinalengthenedposiJonfor2weeks

Early(aer2days)increaseincollagenaerimmobilizaJoninashortenedposiJon

ChangesaNributedtoincreasedperimysium AeroneweekofimmobilizaJon,endomysiumincreased OrientaJonofcollagenfibersmuchmoreacutethaninnormal

muscleasaresultofshortening ImmobilizaJon(shortened)hasadirectimpactonconnecJve

Jssue!! However,muscleimmobilizedinalengthenedposi8onwasnot

affected!


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Discussion: ChangesinpassivetensionproperJesofimmobilizedmuscle

areaccompaniedbychangesinconnecJveJssuecomponents

ofthemuscle ImmobilizaJonhasadirecteffectonconnecJveJssue

Ie,connecJveJssueisntsimplyredistributedaershortening ThesamechangesareOTseeninmuscle

immobilizedinalengthenedposiJon,therefore

reducedacJvityitselfisnotthesJmulusforchange. Rather,thelimbposiJonduringimmobilizaJonaffectsthe

connecJveJssue. QuanJtaJveandqualitaJvechangesassociatedwithshortened

immobilizaJonmayreduceelasJcityofconnecJveJssue


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TransverseTubularSystem

Channelsaroundmyofibrils

Penetratecellsashollowtubules

ConductacJonpotenJalsfromcellsurfacetocellinterior Signalsarcoplasmic

reJculumtoreleasecalcium


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SarcoplasmicReJculum

SmoothendoplasmicreJculum

Paralleltolongaxisofmusclefibers

Storesandreleasescalciumintothecytosol

formusclecontracJon

Fig. 8-10, p. 261


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CalciumReleaseChannelsareCalled

RyanodineReceptors

1. Musclecellmembranedepolarized

2. APdownT-tubules3. Ca2+releasedfromSR4. Ca2+bindswithtroponin

duringcontracJon

Fig. 8-11, p. 261


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RyanodineReceptorthecalciumreleasechannelinthesarcoplasmicre8culum

WhenmusclecontracJonsend,calciumisresequesteredintheSR. Thistakesenergy,ie,usesATP

ViaATPasepumpinSRmembrane Calciumbindstoaprotein,

calsequestrine,intheSR.


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ucleiandMitochondria

Musclefiberscontainnumerousnuclei ucleiaredispersedalongtheinnersurfaceof

thesarcolemma ucleiaremoreconcentratedaroundthe

motorendplate

Mitochondriaareabundantinthecytoplasm


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DuchennesMuscularDystrophy

Arecessive,XchromosomegeneJcdefectAffects1in3000malesDiagnosedin4thor5thyearoflifeResultsinprogressiveweakness,withproximal

musclesaffectedfirst

Deathoccursbyearly20s


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DMD

Tearsarefoundinthesarcolemmaofthemusclefibers

CalciumenterscellsthroughtearsEnzymeprocessesofcellsdisruptedecrosisensues,withscarringofmuscle


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Whatcausesthetearsinthemembrane?

DeleJonsintheXchromosome

Xchromosomecodesfordystrophin


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DMD

DystrophinisaproteincodedforontheXchromosome

DystrophinaNachestoplasmamembraneviaglycoproteins

Itisastructuralproteinthatprovidesamechanicallinkagebetweenthecytoskeletonandtheextracellularmatrix

Dystrophinreinforcesthesarcolemma(plasmamembrane)

preventstearsinsarcolemma


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DMD

Dystrophinalsofoundinthebrain20to30%ofchildrenwithDMDfallintomild-

retardaJoncategory


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PredicJveFactorsofCessaJonofAmbulaJon

inPaJentswithDuchenneMuscular

Dystrophy

BakkerP,deGrootIM,BeelenA,LankhorstG; AmJPhysMedRehabil.2002:81:906-912.

Childrenwithimpairedhipextensionare11.5JmesmorelikelytostopambulaJng

within2years

Impairedankledorsiflexionstrengthmakeschildren3.7Jmesmorelikelytostop

ambulaJngwithin2years

muscle structure 11

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