Vertebrate Skeletal Muscle Structure

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1 VertebrateSkeletalMuscleStructure HumanAnatomy&PhysiologyLab#1 Todaywewillexaminethemuscularsystemoftherat,withparticularemphasison themusclesofthehindlimb.thegoalofthislabistoconsidertherelationship betweenfineandgrossmusclestructureandfunction.byfocusingonrathindlimb muscletoday,youwilllearngeneralprinciplesofmusclestructureandfunction.in addition,therearemanysimilaritiesbutalsoafewinterestingdifferencesbetween theanatomyofthelegintheratandinhumans. Musclecellsdevelopembryonicallyfrommesenchymecells,whichformmyoblasts thatbecomemyocytes,ormusclefibers.basedonfiberstructure,thereare3 generaltypesofmuscle:1)skeletal,2)cardiac,and3)smooth. Cardiacmuscleisfoundinthewallsoftheheart.Smoothmuscleisfoundinthe wallsofbloodvessels,andinsomevisceralorgans.skeletalmusclefibershavea complexorganizationintodistinctunitsormuscles.skeletalmusclesattachdirectly totheskeletonorindirectlyattachviatendons(whichareextensionsofconnective tissueinthemuscle).theoriginofalimbmuscleisitsproximalend;theinsertionis itsdistalend.usuallyskeletalmusclesarearrangedingroupsof agonists/antagonists:onemuscle(theagonist)pullsonastructureinonedirection andthesecondmuscle(theantagonist)pullsonitintheotherdirection(e.g.,the tricepsbrachiiisanantagonistofthebicepsbrachii). Eventhoughwearefocusingonthemuscularsystemoftheratitisimportantto notethattherearesignificantdifferencesbetweensomeofthemusclesoftherat(a quaruped)andahuman(abiped),thesedifferencesarefoundinboththehindlimb andinthemusclesofthebackandshoulders.inthehindlimbthemajordifferences betweentheratandthehumanaretherelativemassesofsomeoftheproximalhip musculature.thehamstringmusclesmakeupthelargestmusclegroupintherat andincludethebicepsfemoris,thesemitendinosusandthesemimembranosus.in theratthehamstringmusclesaretwiceasmassiveastheantagonisticgroupof musclesthequadriceps(vastuslateralis,vastusmedialis,rectusfemoris,vastus intermedius).inhumansthistrendisreversedandthequadricepmusclegroup weighsapproximatelytwiceasmuchasthehamstrings. Similarlythegluteusmaximusinquadrupedsisarelativelysmallmuscleandit accountsforonly6%ofthemassofthemusclesactingatthehip.inhumansthe gluteusmaximusisthelargestmusclethatactsonthehipjointanditaccountsfor 18.3%ofthemusclemassthatiscapableofactingatthehipandisthoughttoplay animportantroleinhumanrunning(liebermanetal.,2006).inadditionhumans aremissingthecaudifemoralis.anatomicalvariationbetweentheratandthe humancanalsobefoundinthemusclesofthebackandshoulders.intheratthere arethreetrapeziusmusclesthespinotrapezius,theacromiotrapeziusandthe

2 clavotrapezius.inthehumanthereisonlyonelargetrapeziusmusclecalledthe spinotrapezius.intheratthereisalsothreedifferentdeltoidmusclesthe spinodeltoid,theacromiodeltoidandtheclavodeltoid.inthehumanthereisonlyone deltoidmuscle. OBJECTIVES 1)Removetheskinfromtherattorsoandlimbs. 2)DissecttherattoexposethemuscleslistedinTable1.Dissectthemuscles. 3)FindthemusclesinTable1ontherat,andonhumandiagrams. Understandtheirbasicanatomy(e.g.,originandinsertion),function(e.g., flexor/extensor),andhowtheydifferinratsandhumans. 4)Demonstrateyourmasteryofthematerialbytakingaquizattheendof lab. DissectionTips RelyprimarilyonyourfingersandthebluntprobeandNOTthescalpel. Youcanbeprettyroughaslongasyouteartissuealongitsnatural boundaries. Ifyoumustmakeacut,holdthescalpellikeapencil.Useyourotherfingers tocontrolyourcut.don tcutanythingunlessyoucanseebelowitandknow whatyouarecuttinginto!agoodtechniqueistoinsertthebluntprobedeep towhateveryou recuttinganduseitasaguide.youcancutalongorbeside itandknowthatyouaren tcuttinganythingdeeperthanyouthink. Separatethemusclesalongtheirnaturalboundariesbyusingthesheets ofconnectivetissueencasingthemuscles(fascia),andmusclefiber orientation.minimizethenumberofcutsyoumakethroughmuscles,and onlycutafteryouhavedeterminedtheidentity,originandinsertionofthe muscle. Whenitisnecessarytoremoveamuscle,alwayscutmusclesbygoing straightthroughthebelly,asperpendicularaspossibletotheorientationof thefibers,andequidistantfromtheoriginandinsertion.withthistechnique, thelocationoftheoriginandinsertionispreservedandthemusclecanbe replaced byfloppingthehalvesofthemusclebackintoplace.

3 Instructions Beginbyremovingtheskinfromtheratthenusingyourlabmanualtoidentifythe superficialmuscleintable1.selectwhichforelimbandhindlimbyouaregoingto dissectandremoveanyadditional,superficialfatand/orconnectivetissuefromthe surfaceofthepelvis,thighandshank.removefatpadslateraltothetailbaseandin thedepressionbehindtheknee. FindthemuscleslistedinTable1.Youcanmakenotesonandaddfurtherdetail tothefollowingdiagrams.refertothehumanskeletonsformuscleattachments andfunctions,andbesuretoreviewtheactionofeachmuscleasyoudelineateit. Youhaveatyourdisposalthedrawingsinthelabmanual,aswellasyourTF.Use thesetofindthemusclesintherat.youmayalsowanttoreadthetexttohelpyouif yougetlost.whenyouarefindingthemuscleslistedintable1onthehuman,or justforamoredetailedunderstanding,youcanalsorefertothecopiesofnetter s guidetohumananatomy.fortheexamyouareresponsibleforallthemuscles onboththeratandhuman,themusclesoriginandpointofinsertion. Muscle group Muscle Key to finding Gluteals Gluteus medius Locate the gluteus superficialisand look below it. Also move the femur Gluteus superficialis (gluteus maximus in humans) Quadriceps Rectus femoris Reflect the fascia latae. It is theonly quad that DOESN T insert on the femur. Vastus lateralis Vastus medialis Reflect the fascia latae and palpate the femur, this muscle will be anterior to the femur. Reflect the sartorius and palpate the femur, this muscle will be anterior to the femur Superficial leg flexors Hamstrings Gracilis Semitendonosus Semimembranosus Caudalmost muscle of the thigh Biceps femoris Palpate the femur from the lateral side, the fibers inserting posteriorly will be the Biceps femoris Hip Adductors Adductor magnus Palpate the femur from medial side, these fibers will insert below the Vastus medialis

4 Foot Extensors Gastrocnemius Muscle with two heads (medial and lateral) Soleus This is the only monoarticular muscle of the Triceps surae Foot Flexor Tibialis anterior Located on the anterior surface of the tibia. Brachium Upper Arm Triceps brachii Be sure to find all three heads of this muscle Biceps brachii Located deep to the pectoralis Lower Arm Pronator teres Muscle responsible for pronating the lower forelinb Palmaris longus Central muscle on the anterior forelimb Dorsal Thorax & Abdomen Spinodeltoid Spinodeltoid fibers travel at right angles to the fibers of the other two deltoid muscles. Latissimus dorsi Large, sheet-like muscle that covers most of the dorsal surface of the thorax. Rhomboids These muscles connect the skull and vertebral column to the scapula. Supraspinatus Reflect the muscles covering the scapula and locate the spine of the scapula; the muscle located on the scapula anterior to the spine is the Supraspinatus Infraspinatus Reflect the muscles covering the scapula and locate the spine of the scapula; the muscle located on the scapula posterior to the spine is the Infraspinatus Teres major Connects the posterior border of the scapula to the humerus Thoracic trapezius This muscle inserts on the scapula and lays over top of the latissimus dorsi. Ventral Thorax Pectoralis superficialis Pectoralis profundus This muscle has two portions an anterior and posterior portion. Part of this muscle is located deep to the pectoantebrachialis Located posterior to the pectoralis major. Serratus ventralis Muscle has a serrated appearance and is located along the lateral side of the ribs. Head & Neck Muscles Masseter Sternomastoid Large chewing muscle located in the cheek Superficial neck muscle which forms a V shape

5 Abdominal Muscles Rectus abdominus External oblique Internal oblique Transversus abdominus These muscles travel parallel to each other on either side of the linea alba. First layer of lateral abdominal muscles. 2nd layer, should be perpendicular to external obliques May be difficult to find, will be just inside parietal peritoneum. Commontermstodescribetheactionofamuscle Extensor:straightenjoints Flexor:bendjoints Adductor:moveappendagestowardthemediansagittalplane Abductor:moveappendagesawayfromthemediansagittalplane Pronator:turnthedorsalsurfaceofalimbanteriorly Supinator:turntheventralsurfaceofalimbanteriorly Levator:raisestructures(Pleasenotethespelling levator,not elevator.) Depressor:lowerstructures References: Homberger,D.G.andW.F.Walker,Jr.2004.AnatomyandDissectionoftheRat.W.F. Freeman.122pages. Lieberman,D.E.,Raichlen,D.A.,Pontzer,H.,Bramble,D.M.andCutright Smith,E. (2006).Thehumangluteusmaximusanditsroleinrunning.JExpBiol209,