TransverseTubulesNucleusIbandAband-ZdiscMitochondriaOpeningsintotransverseSarcoplasmictubulesreticulumTriadTerminalcisternaeTransversetubuleSarcolemma-SarcoplasmMyofibrilsTransverse Tubules.Thesearetubulesformedby invaginations ofthesarcolemma and flankedbythe sarcoplasmicreticulum.Theycarryactionpotentialsdeepintothemusclefiber.TheTtubulesand sarcoplasmic reticulumprovidetightlylinked signalsformuscle contraction.ThereareTtubulesateachAband/Iband junctionandtheyarecontinuouswiththesarcolemma..They conduct electrical impulsestothethroughout cell (every sarcomere);the electrical impulse signalsforthereleaseofCa2+fromadjacentterminalcisternae
Transverse Tubules
MyosinandActinFilamentsActin-binding siteMyosinATPasesiteBinding site foattachmentwith.myosircrossbridgeActinmoleculesHeads100nm(a) Myosin.moleculeActinheloCrossbridgesXMyosin molecules8Troponinropomvosin(b)Thick filamentThinfilament1.Thickfilaments(16nm)calledmyosinDuringmusclecontraction,themyosinheads linkthethick andthinfilamentstogether,formingcrossbridgesEachmyosinmolecule(twointerwovenpolypeptidechains)hasarodliketailandtwoglobularheads2.Thinfilaments(8nm)calledactinActinprovidesactivesiteswheremyosinheadsattachduringcontraction.TropomyosinandTroponinareregulatorysubunitsboundtoactin
Myosin and Actin Filaments