Week 4 KIN 4430 PDF - Muscle Physiology

Majorsteps controlpoints in Pathway ofVoluntary movement UMN in motorcortexwill fire andsendAPs along descending pathways fromthebrain to thespinalCor Thesesteps can becontrolpoints modifythe outco...

Majorsteps controlpoints in Pathway ofVoluntary movement UMN in motorcortexwill fire andsendAPs along descending pathways fromthebrain to thespinalCor Thesesteps can becontrolpoints modifythe outcom atdifferentstepsalongtheway MNS are part ofcentralsystem butaxons arelongand are alsopart oftheperipheral system takesabout 30 35ms to getfromthought action proximalmusclesshouldreactfastersinceits afaster transmissiondowntheaxon Spinal LMNs sendAPstothemuscle CanrecordtheelectricalpotentialoveryourmusclesbyE 4givesideasofelectricaldrivethatcomestothemuscle Canalsorecordforceoutputofthemuscle Finalcommonpathway 4tellswhatthemuscle iscapableofdoing RecordingforceEMGcanbeusedtogethertofigureout what a motorneuron isdoing during a specifictask En fh finalcommonpathway The Motor Unit Thinks offhand a'think n'eafahfoft.it ralfEn i.e controlledby theCNS vs sarcomere main controllable element in the pathway which determines theforceoutput ofthe muscles muscleshave 100s of MUs sarcomeres are the anatomical units of contraction not controlled by the CNS 1 motoneuroncan innervate abunch ofmusclefibres but III To been the ifeng.IS nofYmtacem f8eYhtendon if eachmotoneuron onlyinnervatedonefibre thefinalcommonpathway to create an outputmuscle contraction is from the LMN spinalMNI to the muscle anddepends on drivefromhighercentres UMN plus sensory feedback allmusclefibresfromone unit are ofthesame type MVtypes 4 fast slow intermediatetypes motoneurondeterminemusclefibretype sinceall thefibres in the4999918941Yaumtery have to change innervation if you want to change filIntagethe nervesupply to a muscles can change alltffbrefbff.tt muareactivatedusually simultaneously  size of MV innervation ratio kind of controlneeded finecontrolmuscleshavemoreMUSand lessfibres unit eyemovements biggercontrol muscles havemore fibres unit sincetheyneedmoreforce muscletensionisproportionaltothesize oftheMV finecontrol is inversely proportional tosize MVterritorydispersed over a relatively concentratedarea ofthemush 141444 49 Men'd bethnakhrated on theperiphery ofthemuse SOslowmotortypestendtobemorecentrallydeeplylocated in themuse theywant 0 frombloodsupply sothey'redeeper in musclenear fffafff ficationwithin a muscle Stfibrestendto bemore VariabilityAmongPeopleinMVtypes muscle type I slowtwitch humans are majoritymadeupof Stfibres designed forendurance canmakeslowerfibresfasterandfasterfibresslower butcan'treallyswitchtheactualtypesunlessyou ILL faithg'eh based Properties of MuscleRelatedto Movement Lengthtensionrelationship atthesarcomere level II It's c m trial Infecting'eneratemuch forcesincethere's nowhereelsefor themyo filamentsto 1 cute gocan'tshortenanymore ifthe sarcomere is reallylong can'tgeneratemuch tensiondueto nooverlap thingsaretoostretched andnocrossbridgescanbeformed optimalsarcomerelength decentoverlapopportunity togeneratetensionbyshortening cangenerateforce sarcomeres are a contractileelement oftheHillmodel  WholeMuscle Length Tension Load velocity Relationship longermusclesmoretension 4th asyoustartstretchingthemuscle longertherearenon contractile elements elasticCT athsion yougeneratemore moretension asyoustretchthemuscledueto passivetension passiveproperties thepassive activetensioncurves areaddedtogetherforthetotal muscletensioncurve do'slarge thecurvestopsatmax eventhoughthesarcomere one orthemusclewould getpulledapartandcan't Nothing doesnt fifty isometric contractioncan'tshorte earandtheforcewouldgo generatemuchtensionasthe orlengthen nomovement musclestretchesmore the different differentmuscles if theresistance isless morevelocity0 in passiveparts takeoverand generatetheforce shortening neh flat a ffect if there isnoload Vmax maxvelocit utput ofshortening Force velocity Relationship 1001 maxtensionwithnothinghappening isometriccontracti max velocitytheres noloadtension o at lengthening contraction eccentric generatemoretension but plateaus soyoudon'ttearthe Yehitatemoreforce takesadvantage of passiveproperties ofthemuscle fat a move you eccenin speed of shortening is dictated by theresistance Power EYE FYI of'd tgwkki.EEYasftaiEei mmeaasuredinwatts is at about half ofVmax andLoad peakpower max power is a functional measureformovementthat combines speed velocity withforcetorque MUscontrolthespeed strengthandthepowerofcontractions Electromyography SurfaceEMG recordduringmusclecontractiontosee all the astheforce theelectricalactivity in parallelprettymuch 4 moreforceoutput moreMVactivated more MNS moreelectricity can'tdistinguish individualMUcontributionwe doesn't muscle summation of electricalactivity ofmany  synchronously activatedMUS linearrelationship btwnforceandEMG intramuscularEMG Sticks aneedleintothemuscle directlyrecords theAPs selectiverecording ofindividualactivated MUs trains ofAPs rate offiring yy go.fr bigMNShave ahigherinnervationratioformusclefibre a tendto befasttwitchfibres morefor ÉfÉÉ In Ya his ftp.feshpinfhgrates Intermediatefibres innervationratio issmaller smaller Slowtwitchfibres evensmallerinnervationratio 4shocktomusclecauses asmallerandslowertwitch intrinsicshorteningcapacityisslower propertiesreflecttheweighted su 6 1 18 4fi Yfhf MuscleForce Gradation Two mechanismsused bytheCNS I Teach heh off fruittern In'ashgingfaith native 2 M I y rate or frequency of MVAPtrains temporalsummation CNSuses a combo ofthese a train ofAPs Into gffhkhutshcfeffbtefhtisaffethdnate.freaglehe force anotherMV is recruited and so on someMugetactivated at lowforces some at higherforces recruitment adding more MV derecruitment theMusdropout in reverseorder order will always bethe same for recruitment flowforcethresno Each u e differentforcethresholds Activation History muwillberecruited at a certainforcebutdon'tstopbe force activateduntilalower itshardtoactivateMUSfromrestand itdoesn'twant soyouhavetogoto a lowerfor 9m It fixated MUhaveApfiring rateonceactivated Activationhistoryaffectshowthesystemresponds Derecruitmentthreshold is usually lower than recruitmentthreshold differentstrategyisuseddependingonactivation history Force MVRecruitment force recruitment ofMV's until1001force relationshipisn'tlinear smallMu recruitedfirst andtheydon'thaveasmanymusclefibr so notmuchforceproduction untilbiggerMUSare recruited of MUswould all have to be thesamesizefor a linearrelationsh SmallerMV 1strecruited lastderecruited orderlyrecruitment allowsthesystemto bepredictable localspinalcontrol determ theorderlyrecruitment vs highercentres onedoesn'thavetothin whichMUs to recruitfirst ffhffffffhh.int relatedto size ofMNsIsmailMushavesmalleraliveandcell bodies Henneman Sizeprinciple ofthecurrent Proportionalcontrol eachMVrecruitedequals a fixed EYE a9YmaYerr Yitedlateraddrelatively In LargeMU bigcellbodies longaxon lotsofmusclefibres morefor neaPcEfdensity Ye's 489 Hidetrate 914fYIIFanff.rs SmallMU membrane becomes more excitableeasier biggerSAthanvolume smallercellshavehighersynapticdensities andexcitato current is concentrated along a smallermembranewhich reachesthreshold ofexcitementsoonerthanlargecells CNSsends afixedamountofinputbutthatmayonlybe enough toactivatesmallercells havetoincreaseinput 9Yn tothinkaboutbasicmput Cycling Vastus Lateralis glycogendepletion in m fibres exceptbiggestMUs Its hard to recruitlarg MUsandtherestoftheM poolmightbeexhausted before BiggerMu arehardto activateand All MVtypes areused b don'tstayforlong IIB areusedmuch type