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Muscle System B

Muscle System B. Ch 9. Sarcolemma. Cell membrane of the muscle fiber Responds to motor neurons Conducts contraction signals. Sarcoplasm. Muscle cytoplasm Contains organelles Mitochondria High concentration Nuclei Multiple Peripheral Transverse tubules Sarcoplasmic reticulum

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Muscle System B

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  1. Muscle System B Ch 9

  2. Sarcolemma • Cell membrane of the muscle fiber • Responds to motor neurons • Conducts contraction signals

  3. Sarcoplasm • Muscle cytoplasm • Contains organelles • Mitochondria • High concentration • Nuclei • Multiple • Peripheral • Transverse tubules • Sarcoplasmic reticulum • Myofibrils

  4. Peripheral Nuclei

  5. Transverse Tubule • Invagination of sarcolemma into the cell • Communicate with all myofibrils • Conducts action potential to cell interior • Distributes contraction signals throughout cell • Communication efficiency • Coordination of muscle contraction • Fluid filled • Specialized interaction with endoplasmic reticulum • Sarcoplasmic reticulum

  6. Invagination of Sarcolemma

  7. Communicates with Sarcoplasmic Reticulum

  8. Sarcoplasmic Reticulum • Specialized Endoplasmic Reticulum • Stores & releases calcium • Terminal Cisternae • Enlarged region of SR • Stores & releases the majority of Ca+ • Connects with T-tubule to form Triad • Arrangement of SR & T-tubule

  9. Sarcoplasmic Reticulum

  10. Terminal Cisternae

  11. Triad

  12. Myofibril Structure • Protein filaments & motor proteins used in muscle contraction • Myofilament • bundles of protein filaments • Highly organized microfilaments • Work in conjunction with motor proteins • 100-1000+ of myofilaments per myofibril • Change orientation to produce muscle contraction • Active unit • Use ATP

  13. Myofilament • 2 types fibers • Actin- thin filaments • Primarily actin protein • Contain active site • Myosin- thick filaments • Primarily myosin protein • Contain myosin heads • Motor proteins- active site • Tropomyosin • Troponin

  14. Actin Strands with Motor Proteins

  15. Myosin Strands

  16. Mysosin Heads

  17. Myofilament Organization • Parallel overlapping arrangement • Organization produces striation pattern • Arranged in sarcomeres

  18. Parallel

  19. Overlapping

  20. 3 Dimensional

  21. Sarcomere • Unit of myofilaments • Comprised of thick & thin fibers • Functional contractile unit • Sarcomere changes length • Protein fibers that make up sarcomere do not change length • 1000s+ make up myofibril • Each contract in coordination with other sarcomeres to create muscle contraction • Distinct organization patterns

  22. Sarcomere

  23. Sarcomere Structure • Overlapping fibers with thick filaments in the center & thin filaments on either side • Z line • Protein ends mark boundary of sacromere • Thin filaments attach here • M line • Connect thick filaments • A band • Thick & thin filaments • I band • Thin filaments only • H band • Gap between thin filaments

  24. I band • Isotropic • Thick light outer band • Comprised of only thin filaments • Gets smaller during contraction

  25. A Band • Anisotropic • An= not • Thick dark central band • Comprised of both thick & thin filaments • Remains the same during contraction

  26. Z Line • Aka Z Disc, Zwischen Scheibe • Zwischen= disc Scheibe= inside • Dark, outer boundary of sarcomere • Region of interlocking thin filaments • Move closer together during contraction

  27. H Band • Aka H Zone • Thin, light, middle band • “middle of sarcomere” • Comprised of thick filaments only • Gets smaller during contraction

  28. M Line • Thin, dark, middle line • Region of interlocking thick filaments • Does not change during contraction

  29. Zone of Overlap • Area where thick and thin filaments overlap • Increases during muscle contraction

  30. Striation


  32. Muscle Contractions • Cumulative shortening of each sarcomere • Actions of myofilaments & motor proteins cause filaments to move against each other in a sliding fashion • Sliding Filament Theory • Coordinated movements • Occur in unique sequence of events triggered by electrical signal

  33. Response Conduction Contraction

  34. Response • Responds to motor neurons • Neuromuscular junction • Site of communication with motor nerves • motor end plates • Motor end plates • High density of receptors • Respond to nerve signal • Neurotransmitters • Ex Ach: Acetylcholine


  36. Conducts • Conducts contraction signals to myofibrils in sarcoplasm • Signal is an electrical current • Action potential • Region of specialization to maximize communication efficiency • Transverse tubule (T Tubule) • Communicates signal to myofibrils

  37. Contraction • Sliding Filament Theory • Contraction a result of coordinated sarcomere shortening • Sarcomere, not filaments change in length • Thin filaments slide inward across thick filaments • Slide over thick filaments • Increase zone of overlap • Produce shortening of sarcomere

  38. Contraction of Sarcomere

  39. “Sliding” • Interaction between thin & thick filaments • Active site • Found on thin fibers • Tropomyosin & Troponin • Will interact with myosin heads to create contraction • Connection with myosin forms cross bridge

  40. Active Site

  41. Cross Bridge Formation

  42. Muscle Contraction Produces Force

  43. Myotonia Congenita • Lack of muscle relaxation after contraction •

  44. Muscle Contraction • Uses both chemical & electrical signal • Signal received at sarcolemma and travels to the interior of the cell via T tubules • T Tubules interact with sarcoplasmic reticulum at the cisternae • Trigger release of stored calcium from triad region • Calcium binds with troponin & causes exposure of active site • Myosin cross bridge formed when myosin heads attach to exposed active site • Movement (contraction) • ATP molecule attaches to release cross bridge

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