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Lecture 7: Chapter 10 Muscle Tissue Pages: 283-325

Lecture 7: Chapter 10 Muscle Tissue Pages: 283-325. Lecturer: Dr. Barjis Room: P313 /P307 Phone: (718)2605285 E-Mail: ibarjis@citytech.cuny.edu. Learning Objectives. Describe the organization of muscle and the unique characteristics of skeletal muscle cells.

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Lecture 7: Chapter 10 Muscle Tissue Pages: 283-325

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  1. Lecture 7: Chapter 10 Muscle TissuePages: 283-325 Lecturer: Dr. Barjis Room: P313 /P307 Phone: (718)2605285 E-Mail: ibarjis@citytech.cuny.edu

  2. Learning Objectives • Describe the organization of muscle and the unique characteristics of skeletal muscle cells. • Identify the structural components of the sarcomere. • Summarize the events at the neuromuscular junction. • Explain the key concepts involved in skeletal muscle contraction and tension production.

  3. Learning Objectives • Describe how muscle fibers obtain energy for contraction. • Distinguish between aerobic and anaerobic contraction, muscle fiber types, and muscle performance. • Identify the differences between skeletal, cardiac and smooth muscle.

  4. Skeletal muscle tissue and the Muscular System Three types of muscle • Skeletal – attached to bone • Cardiac – found in the heart • Smooth – lines hollow organs

  5. Skeletal muscle functions • Produce skeletal movement • Maintain posture and body position • Support soft tissues • Guard entrances and exits • Maintain body temperature

  6. Anatomy of Skeletal Muscle Organization of connective tissues • Epimysium surrounds muscle • Perimysium sheathes bundles of muscle fibers • Epimysium and perimysium contain blood vessels and nerves • Endomysium covers individual muscle fibers • Tendons or aponeuroses attach muscle to bone or muscle Animation: See tutorial

  7. The Organization of Skeletal Muscles

  8. Skeletal muscle fibers • Sarcolemma (cell membrane) • Sarcoplasm (muscle cell cytoplasm) • Sarcoplasmic reticulum (modified ER) • T-tubules and myofibrils aid in contraction • Sarcomeres – regular arrangement of myofibrils

  9. The Structure of a Skeletal Muscle Fiber

  10. Sarcomere Structure, Part I

  11. Myofibrils • Thick and thin filaments • Organized regularly

  12. Sarcomere Structure, Part II

  13. Levels of Functional Organization in Skeletal Muscle Fiber

  14. Thin filaments • F-actin • Nebulin • Tropomyosin • Covers active sites on G-actin • Troponin • Binds to G-actin and holds tropomyosin in place

  15. Thick filaments • Bundles of myosin fibers around titan core • Myosin molecules have elongate tail, globular head • Heads form cross-bridges during contraction • Interactions between G-actin and myosin prevented by tropomyosin during rest

  16. Thick and Thin Filaments

  17. Sliding filament theory • Explains the relationship between thick and thin filaments as contraction proceeds • Cyclic process beginning with calcium release from SR • Calcium binds to troponin • Trponin moves, moving tropomyosin and exposing actin active site • Myosin head forms cross bridge and bends toward H zone • ATP allows release of cross bridge

  18. Changes in the appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber

  19. The Contraction of Skeletal Muscle Tension • Created when muscles contract • Series of steps that begin with excitation at the neuromuscular junction • Calcium release • Thick/thin filament interaction • Muscle fiber contraction • Tension

  20. An Overview of the Process of Skeletal Muscle

  21. Control of skeletal muscle activity occurs at the neuromuscular junction • Action potential arrives at synaptic terminal • ACh released into synaptic cleft • ACh binds to receptors on post-synaptic neuron • Action potential in sarcolemma

  22. Skeletal Muscle Innervation

  23. Skeletal Muscle Innervation Animation: See tutorial

  24. Excitation/contraction coupling • Action potential along T-tubule causes release of calcium from cisternae of SR • Initiates contraction cycle • Attachment • Pivot • Detachment • Return

  25. The Contraction Cycle

  26. The Contraction Cycle

  27. The Contraction Cycle

  28. The Contraction Cycle

  29. Relaxation • Acetylcholinesterase breaks down ACh • Limits the duration of contraction Animation: See tutorial

  30. Tension Production Tension production by muscle fibers • All or none principle • Amount of tension depends on number of cross bridges formed • Skeletal muscle contracts most forcefully over a narrow ranges of resting lengths

  31. The Effect of Sarcomere Length on Tension

  32. Twitch • Cycle of contraction, relaxation produced by a single stimulus • Treppe • Repeated stimulation after relaxation phase has been completed

  33. Summation • Repeated stimulation before relaxation phase has been completed • Wave summation = one twitch is added to another • Incomplete tetanus = muscle never relaxes completely • Complete tetanus = relaxation phase is eleminated

  34. The Twitch and the Development of Tension

  35. Effects of Repeated Stimulations

  36. Tension production by skeletal muscles • Internal tension generated inside contracting muscle fibers • External tension generated in extracellular fibers

  37. Internal and External Tension

  38. Motor units • All the muscle fibers innervated by one neuron • Precise control of movement determined by number and size of motor unit • Muscle tone • Stabilizes bones and joints

  39. The Arrangement of Motor Units in a Skeletal Muscle

  40. Tension production by skeletal muscles • Internal tension generated inside contracting muscle fibers • External tension generated in extracellular fibers

  41. Internal and External Tension

  42. Motor units • All the muscle fibers innervated by one neuron • Precise control of movement determined by number and size of motor unit • Muscle tone • Stabilizes bones and joints

  43. The Arrangement of Motor Units in a Skeletal Muscle

  44. Contractions • Isometric • Tension rises, length of muscle remains constant • Isotonic • Tension rises, length of muscle changes • Resistance and speed of contraction inversely related • Return to resting lengths due to elastic components, contraction of opposing muscle groups, gravity Animation: See tutorial

  45. Isotonic and Isometric Contractions Figure 10.18

  46. Resistance and Speed of Contraction Animation: See tutorial

  47. Energy Use and Muscle Contraction Muscle Contraction requires large amounts of energy • Creatine phosphate releases stored energy to convert ADP to ATP • Aerobic metabolism provides most ATP needed for contraction • At peak activity, anaerobic glycolysis needed to generate ATP

  48. Muscle Metabolism

  49. Muscle Metabolism

  50. Energy use and level of muscular activity • Energy production and use patterns mirror muscle activity • Fatigued muscle no longer contracts • Build up of lactic acid • Exhaustion of energy resources

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