BIOL 460 1st Edition Lecture 14 Outline of Last Lecture I Priming Effect a Upregulation b Downregulation c Paracrine regulation i Prostaglandins ii NSAIDS iii Isoenzymes Outline of Current Lecture I Skeletal Muscle a Myofibers i A bands ii I bands b Mechanism of muscle contraction c Cross bridge cycling Current Lecture Skeletal Muscle 1 2 3 4 Innervated by somatic motor neurons Conscious control Important in movement and generation of body head Figure 12 1 a Lots of connective tissue involved These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute i Outer surface Epimysium dense layer of connective tissue ii Inside of muscle Perimysium divides into units called fasciculi iii Within one fasciculus there are multiple muscle cells 1 Each cell muscle fiber myofiber 2 Each surrounded by thin connective tissue called endomysium iv Tendon continuation of epimysium and perimysium after muscle stops connects to bone v One connects to origin stationary and the other to the insertion moves Myofibers 1 Very long can extend centimeters 2 Same diameter as other cells 3 Myoblasts arrange in horizontal rows and fuse together see notes a Multinucleate b Syncytium fused together c Sarco flesh i PM sarcolemma ii Cytoplasm sarcoplasm iii ER Sarcoplasmic Reticulum d Striated i Dark red bands A bands ii Lighter bands I bands e Each myofiber contains structures that look like spaghetti myofibrils i All in center ii Nucleus shoved to outside along w sarcoplasm and SR iii Myofibrils are composed of subunits called sarcomeres iv Sarcomeres are in register they all line up v See notes for picture of sarcomere 1 Composed of myofilaments 2 Thin myofilaments actin anchored to z disk 3 Thick myofilaments myosin in center attached by m line protein fibers 4 Cross bridges project out from thick myofilaments 5 Region that only contains thick H zone 6 Just thin I bands 7 Thick and thin A bands 8 Titin runs all the way through largest known protein acts like a string returning sarcomeres to resting length f Mechanism of Muscle Contraction i Sliding filament theory ii When a muscle contracts it gets shorter because fasciculi get shorter iii Fasciculi get shorter because myofibers get shorter iv Myofibers get shorter because myofibrils get shorter v Myofibrils get shorter because sacromeres get shorter vi Sarcomeres get shorter because myofilaments slide past each other vii Cross bridges work like oars attaching to thin myofilaments pulling toward center of sarcomere 1 Asynchronous so titin cannot push thin filament back out 2 Z discs get closer together 3 I band gets smaller until it disappears 4 H zone gets smaller until it disappears 5 A band stays the same viii Cross Bridge Cycling 1 Powered by ATP 2 Cross bridge has 2 conformations a Phosphorylated cocked b Dephosphorylated c PHOSPHORYLATION OF CROSS BRIDGE COCKS CROSS BRIDGE d POWER STROKE RESULT OF DEPHOSPHORYLATION e Thick myofilament composed of myosin filaments f 1 myosin has a cross bridge g cross bridge has an ATPase domain and an actin binding domain h ATP hydrolyzed to ADP and P P binds to cross bridge cocking it i Break bond power stroke 3 Thin filament composed of f actin a Polymerized from g actin b Looks like double strand of pearls c Has a myosin binding site 4 Cross bridge cycle FIGURE 12 12 a Phosphate covalently bonds cocks b Attaches to thin myofilament c Attachment triggers dephosphorylation of cross bridge d Causes power stroke which pulls thin myofilament to center of sarcomere and ejects ADP e ATP binds causing cross bridge to detach from thin myofilament 5 Rigor Mortis state of a corpse when muscles are all contracted no ATP is made and no detachment of cross bridges g What prevents cross bridge from attaching i Troponin Tropomyosin complex ii T TC part of thin myofilament iii Tropomyosin is rod shaped iv Troponin complex composed of 1 TNT troponin tropomyosin attaches to tropomyosin 2 TNC troponin ligand binding site to calcium presence contraction 3 TNI troponin interfering interferes with cross bridge attachment a Tropomyosin blocks myosin binding site b TNI move tropomyosin after Ca2 binds c Allows binding to occur