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HumanAnatomy Unit2 MICROSCOPICSKELETALMUSCLEANATOMY InAnatomyToday SkeletalMuscleTissue • Characteristics – Striated – Multinucleate – Voluntary(somatic) • Anatomy – Muscle • Myofiber • Myofibril • Myofilament MuscleMicroanatomy • Multinucleate – Developfromthefusionof multiplemyoblasts – Eachmyoblasthasitsown nuclues • Myofiber – Musclefiber – Musclecell • Myofibril – Tubesofcontractileproteins • Myofilament – Contractileproteins MuscleFiber • Sarcolemma – Membraneofmusclefiber – Electricallyexcitable – T-tubules • Sarcoplasm – Musclecytoplasm • Sarcoplasmicreticulum – ModifiedsmoothER – Lateralsacs – Storescalcium(Ca2+) • Functionalunitofskeletal muscleisthesarcomere SarcomereStructure • Zline – Definesthesarcomere • Aband – Lengthofthickfilament • Hband – Spacebetweenthinfilaments withinasarcomere • Iband – Spacebetweenthickfilaments betweensarcomeres • Thickfilament • Thinfilament • Elasticfilament ThinFilament • 2strandsofactin molecules – Hasbindingsitesfor myosin • Tropomyosin – Coversbindingsiteson actinformyosin – Restingfiber • Troponin – Holdstropomyosininplace – Bindstocalcium(Ca2+) ThickandElasticFilament • ThickFilament – Myosin – Tail – Myosinhead • MyosinHead – 2bindingsites • ADP+pi • Actin • Elasticfilament – Titin – Achorsmyosininplace withinsarcomere MuscleContraction • Slidingfilamenttheory • Myosinheadsbindtoactin – 6thinfilaments:1thick filament • Headschangeconformation andpulltheactinfilaments acrossmyosinmolecule – Discontinuouspulling • Sarcomereshortens – Thickandthinfilamentsdo notshorten! • Allornoneresponse NeuromuscularJunction • Somaticmotorneuron innervatesmusclefiber – Synapticbulb – Vesicles – Acetylcholine(ACh) • Motorendplate – Invaginationof sarcolemma – ReceptorsforACh • 1:1ratio MotorUnit • Asinglemotorneuronand allofthemusclefibersit innervates • Asomaticmotorneuronhas collateralbranchesthat innervatemultiplemuscle fibers • Whenamotorneuron sendsasignaltocontract – Allfibersinthemotorunit willcontract • Amusclewillbecomprised ofmultiplemotorunits – Ratioofmotorunits:muscle SkeletalMuscle NeuromuscularJunction CardiacMuscle SmoothMuscle
