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Skeletal Muscle

Skeletal Muscle. Skeletal Muscle and its Connective Tissue. Approximately 640 muscles in the body Make up about 45% of total body weight Composition 15% connective tissue (fascia) + fat Collagen, elastin, laminin Cytoskeletal proteins that aggregate under sarcolemma 85% muscle fibers.

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Skeletal Muscle

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  1. Skeletal Muscle

  2. Skeletal Muscle and its Connective Tissue Approximately 640 muscles in the body Make up about 45% of total body weight Composition 15% connective tissue (fascia) + fat Collagen, elastin, laminin Cytoskeletal proteins that aggregate under sarcolemma 85% muscle fibers

  3. Skeletal Muscle and its Connective Tissue Composition 15% connective tissue (fascia) + fat Cytoskeletal proteins that aggregate under sarcolemma Integrins, focal adhesion kinase, nitric oxide synthase,dystrophin, paxillin, vinculin, talin Form clumps called “costameres” - signals for growth?

  4. Myocytes – Muscle Cells • Sarcolemma – Membrane surrounding the muscle cells • Sarcoplasm – Cytoplasm of muscle cells Contains: • Multiple nuclei for each cell • Mitochondria • Myofibrils – Threadlike structures containing the contractile proteins Actin and Myosin. • Transverse (T) Tubules – invagination that allows propagation of electrical signal into the muscle cell interior • Sarcoplasmic reticulum- reservoir for Ca++ communicates with T-tubules

  5. Muscle Cells (continued) • Fascia – White, fibrous connective tissue surrounding entire muscles - makes up perimysium and epimysium. • Epimysium – Connective tissue sheath surrounding bundles of fascicles • The epimysium is continuous with the muscle tendons • Perimysium – Connective tissue sheath surrounding fascicles • Endomysium – Connective tissue surrounding the sarcolemma • Fascicles –bundles of muscle fibers

  6. Skeletal Muscle Composition Composition Skeletal muscle fibers 75% H2O 20% protein Contractile Actin Myosin Troponin - binds Ca++ Tropomyosin Metabolic - produce ATP 5% other

  7. Packaging of Skeletal Muscle Fibers and Fascia

  8. Skeletal Muscle Composition • Composition • Skeletal muscle fibers

  9. Packaging of Skeletal Muscle Fibers and Fascia

  10. Muscle - Gross Geometry Muscle section showing geometry of muscle fascia.

  11. Transfer of Forces - Skeletal Muscle Forces are transmitted down the muscle fibers to tendon by: 1. Muscle fibers “interdigitation” with bundles of collagen fibers in tendons Interlocking grip Serial transfer of forces (Series elastic element) High surface area reduces muscle and tendon injuries 2. The cytoskeleton to the extracellular matrix and vice versa Cytoskeletal proteins detect and communicate stress & strain Hoop stress/strength Reduces risk of injury Parallel (transverse or shear) transfer or “hoop strength” (Parallel elastic element)

  12. Muscle section showing the attachment of the tendon to the periosteum and interface between skeletal muscle and tendon. interdigitation

  13. Force Transmittance - Skeletal Muscle • Forces transmitted skeletal muscle --> tendon • (SERIES; longitudinal) • (PARALLEL; transverse) • Reduces risk of injury series parallel Huijing, ESSR, 2003

  14. Cytoskeleton: Path for Force Transmission 8

  15. 4 9 8 10 7 6 Cytoskeleton - transfer forces, cell communication & growth Extra Cellular Matrix (ECM) Out integrins calmodulin Focal adhesion kinase nNOS In

  16. Cytoskeleton: Path for Force Transmission Between Cell and ECM 8

  17. Skeletal Muscle Can Produce Tension • (1) passively - when stretched • due to material properties of the muscle (no activation) • Muscle fibers, cytoskeleton + ECM • (2) actively • Contraction: APs ---> excitation --> contraction

  18. Skeletal Muscle Can Produce Tension • (1) passive tension - causes • Material properties of muscle fibers + connective tissue • Increasing muscle length (stretch) • Speed of stretch • (2) active tension • Contraction: • APs ---> excitation-contraction coupling --> contraction

  19. Passive Tension - recoil • (1) passive tension • Material properties of muscle fibers + connective tissue (epimysium, perimysium, endomysium) • Titin - “spring protein” in muscle fibers • No AP activation - resistance, recoil • Increasing muscle length • Speed of stretch

  20. Passive Tension - recoil • (1) passive tension • Material properties • Titin - “spring protein”

  21. Passive Tension - Length Curve End of ROM Muscles generate maximum tension when stretched to about 120% of resting length

  22. Stress-Strain Curve

  23. Passive Tension - recoil • Speed of contraction - a stretched muscle is a “happy” muscle • (1) When a muscle is stretched rapidly it is able to store, then release effectively elastic force and energy (recoil or spring) • wind-up • (2) When a muscle is stretched slowly it dissipates elastic force and energy • Stretching to increase ROM • Stretching as a warm-up

  24. Passive Tension - recoil • Speed of contraction • Stretched muscles act: • viscoelastic rapidly slowly

  25. Total Tension – Length Curve End of ROM

  26. Length-Tension Relationship • Total muscle tension is a result of the addition of Active and Passive Tension • Muscles generate maximum tension when stretched to about 120% of resting length

  27. Change In Muscle Length Resting Length Stretched Passive Elastic Recoil Concentric Contraction (shortening)

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