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Structure and Function of Skeletal Muscle

Structure and Function of Skeletal Muscle. HND Functional Anatomy Zac Laraman MSMA. Skeletal Muscle. Human body contains over 400 skeletal muscles 40-50% of total body weight Functions of skeletal muscle Force production for locomotion and breathing Force production for postural support

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Structure and Function of Skeletal Muscle

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  1. Structure and Function of Skeletal Muscle HND Functional Anatomy Zac Laraman MSMA

  2. Skeletal Muscle • Human body contains over 400 skeletal muscles • 40-50% of total body weight • Functions of skeletal muscle • Force production for locomotion and breathing • Force production for postural support • Heat production during cold stress

  3. Structure of Skeletal Muscle:Connective Tissue Covering • Epimysium (upon, outside) • Surrounds entire muscle • Perimysium (around) • Surrounds bundles of muscle fibres • Fascicles (bundle) • Endomysium (within) • Surrounds individual muscle fibres

  4. Structure of Skeletal Muscle:Microstructure • Sarcolemma (flesh – husk) • Muscle cell membrane • Myofibrils (muscle – fibres) • Threadlike strands within muscle fibres • Actin (thin filament) • Troponin • Tropomyosin • Myosin (thick filament)

  5. Structure of Skeletal Muscle:The Sarcomere • Further divisions of myofibrils • Z-line • A-band • I-band • Within the sarcoplasm • Sarcoplasmic reticulum • Storage sites for calcium • Transverse tubules • Terminal cisternae

  6. The Neuromuscular Junction • Site where motor neuron meets the muscle fibre • Separated by gap called the neuromuscular cleft • Motor end plate • Pocket formed around motor neuron by sarcolemma • Acetylcholine is released from the motor neuron • Causes an end-plate potential (EPP) • Depolarisation of muscle fibre

  7. Illustration of the Neuromuscular Junction

  8. Motor Unit • Single motor neuron & muscle fibres it innervates • Eye muscles – 1:1 muscle/nerve ratio • Hamstrings – 300:1 muscle/nerve ratio

  9. Muscular Contraction • The sliding filament model • Muscle shortening occurs due to the movement of the actin filament over the myosin filament • Formation of cross-bridges between actin and myosin filaments • Reduction in the distance between Z-lines of the sarcomere

  10. Cross-Bridge Formation in Muscle Contraction

  11. Muscle Function • All or none law – fibre contracts completely or not at all • Muscle strength gradation • Multiple motor unit summation – more motor units per unit of time • Wave summation – vary frequency of contraction of individual motor units

  12. Fiber Types and Performance • Power athletes • Sprinters • Possess high percentage of fast fibers • Endurance athletes • Distance runners • Have high percentage of slow fibers • Others • Weight lifters and nonathletes • Have about 50% slow and 50% fast fibers

  13. Types of Muscle Contraction • Isometric • Muscle exerts force without changing length • Pulling against immovable object • Postural muscles • Isotonic (dynamic) • Concentric • Muscle shortens during force production • Eccentric • Muscle produces force but length increases

  14. Isotonic and Isometric Contractions

  15. Relationship Between Stimulus Frequency and Force Generation

  16. Receptors in Muscle • Muscle spindle • Detect dynamic and static changes in muscle length • Stretch reflex • Stretch on muscle causes reflex contraction • Golgi tendon organ (GTO) • Monitor tension developed in muscle • Prevents damage during excessive force generation • Stimulation results in reflex relaxation of muscle

  17. Muscle Spindle

  18. Golgi Tendon Organ

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