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The Muscular System

The Muscular System. Produce movement or tension via shortening (contraction) Generate heat - body temp 3 types: Skeletal - moves bone, voluntary Smooth Cardiac. Skeletal Muscle Characteristics. Voluntary Most are attached by tendons to bones Synergistic: groups work together

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The Muscular System

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  1. The Muscular System • Produce movement or tension via shortening (contraction) • Generate heat - body temp • 3 types: • Skeletal - moves bone, voluntary • Smooth • Cardiac

  2. Skeletal Muscle Characteristics • Voluntary • Most are attached by tendons to bones • Synergistic: groups work together • Antagonistic: groups oppose each other • Origin, insertion points on opposite sides of joints • Cells are multinucleate, striated

  3. Muscle Structure • Whole muscle • Fascicles: bundles of cells, CT covering on each one • Muscle cells = fibers Figure 6.3

  4. Microscopic Anatomy of Skeletal Muscle • Muscle cells • multinucleate, striated –visible banding • Myofibril - bundles of filaments Figure 6.3a

  5. Skeletal Muscle Contractile Unit • Sarcomere • Actin and myosin • Z Lines: attachment points for sarcomeres Figure 6.5

  6. Nerve Stimulus to Muscles • Skeletal muscles must be stimulated by a nerve to contract • Motor unit • One neuron • Muscle cells stimulated by that neuron Figure 6.4a

  7. Nerve Stimulus to Muscles • Neuromuscular junctions – association site of nerve and muscle Figure 6.5b

  8. Nerve Activation of Muscle Cells • Acetylcholine released from motor neuron • Electrical impulse transmitted along T tubules • Calcium released from sarcoplasmic reticulum Figure 6.6

  9. Calcium Initiates the Sliding Filament Mechanism Figure 6.7

  10. Mechanism of Muscle Contraction (cont.) Figure 6.8

  11. Muscle Relaxation • Nerve activation ends, contraction ends • Calcium pumped back into sarcoplasmic reticulum • Calcium removed from troponin • Myosin-binding site covered • No calcium = no cross-bridges

  12. Energy Required for Muscle Activity • Principle source of energy: ATP • ATP replenished by: • Creatine phosphate • Stored glycogen • Aerobic metabolism of glucose, fatty acids, and other high-energy molecules • Anaerobic use of glucose

  13. Aerobic metabolism • 3 stages to convert energy of glucose to ATP High-energy electrons carried by NADH High-energy electrons carried by NADH GLYCOLYSIS ELECTRONTRANSPORT CHAINAND CHEMIOSMOSIS GLYCOLYSIS KREBSCYCLE ELECTRONTRANSPORT CHAINAND CHEMIOSMOSIS Glucose Pyruvicacid KREBSCYCLE Glucose Pyruvicacid Cytoplasmicfluid Cytoplasmicfluid Mitochondrion Mitochondrion

  14. Muscle Fatigue and Oxygen Debt • A fatigued muscle is unable to contract • anaerobic metabolism produces lactic acid • Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less • Oxygen is required to get rid of lactic acid GLYCOLYSIS 2 Pyruvicacid 2 Lactic acid Glucose

  15. Contraction of a Skeletal Muscle • Muscle fiber contraction is “all or none” • Within a skeletal muscle, not all fibers may be stimulated during the same interval • Graded responses due to: - number of muscle cells in each motor unit - number of muscle cells stimulated - frequency of muscle stimulation

  16. Muscle Contraction: Myogram • Latent period • Contraction • Relaxation • Summation vs. tetanus Figure 6.10

  17. Types of Muscle Contractions • Isotonic contractions • Myofilaments slide past each other • muscle shortens • Isometric contractions • Tension in muscles • muscle is unable to shorten

  18. Muscle Activity • Slow twitch vs. fast twitch fibers • Slow twitch: endurance, long duration contraction, contain myoglobin • Jogging, swimming, biking • Fast twitch: strength, white muscle, short duration contraction • Sprinting, weight lifting, tennis

  19. Exercise Training • Strength training • Resistance training • Short, intense • Builds more fast-twitch myofibrils • Aerobic training • Builds endurance • Increases blood supply to muscle cells • Target heart rate at least 20 minutes, three times a week

  20. Features of Cardiac and Smooth Muscles • Activation of cardiac and smooth muscles • Involuntary • Specialized adaptations • Speed and sustainability of contractions • Arrangement of myosin and actin filaments

  21. Smooth Muscle Characteristics • Has no striations • Spindle-shaped cells • Single nucleus • Involuntary – no conscious control • Found mainly in the walls of hollow organs Figure 6.2a

  22. Cardiac Muscle Characteristics • Has striations • Branched cell with a single nucleus • Joined to another muscle cell at an intercalated disc • Involuntary • Muscle bundles wrapped around heart Figure 6.2b

  23. Diseases and Disorders of the Muscular System • Muscular dystrophy • Tetanus • Muscle cramps • Pulled muscles • Fasciitis

  24. Superficial Muscles: Anterior Figure 6.21

  25. Superficial Muscles: Posterior Figure 6.22

  26. Body Movements • Flexion • Extension • Rotation Figure 6.13a–c

  27. Body Movements • Abduction • Adduction • Circumduction Figure 6.13d

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