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Muscular System

Muscular System. Chp. 6. The Muscular System is very complex:. Figure 6.2. Muscle Function : Produce Movement or Generate Tension. Principle function - produce movement or generate tension Contraction : shorten distances between bones Skeletal muscles function to move bones

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Muscular System

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  1. Muscular System Chp. 6

  2. The Muscular System is very complex: Figure 6.2

  3. Muscle Function: Produce Movement or Generate Tension • Principle function - produce movement or generate tension • Contraction: shorten distances between bones • Skeletal muscles function to move bones • Two major types muscle groups: Synergistic muscles: groups work together Antagonistic muscles: groups oppose each other

  4. Muscle Structure: • Fascicles = bundles of muscle cells surrounded by sheath (connective tissue) • Muscle fibers= few doz.- 1,000’s muscle cells Connective tissue surrounding entire muscle, collectively, these connective tissues form tendons. Figure 6.3

  5. Skeletal Muscle Contractile Unit: • Single muscle cell contains many myofibrils: • ea myofibril is composed of sacromeres • actin filaments • myosin filaments • z-lines

  6. Skeletal Muscle Contractile Unit: • Sarcomere - segment of single myofibril from one Z-line to the next Z-line • Actin - protein w/tropomyosin binding sites • Myosin - thick filament w/ myosin heads • Z Lines - attachment points for sarcomeres • Actin filaments linked with z-line • Myosin filaments located w/in scaromeres

  7. Skeletal Muscle Contractile Unit (cont.) Figure 6.5

  8. Nerve Activation of Individual Muscle Cells: • Acetylcholine released from motor neuron at neuromuscular junction • Electrical impulse transmitted along T tubules • Calcium released from sarcoplasmic reticulum

  9. Nerve Activation of Individual Muscle Cells (cont.) Figure 6.6

  10. Calcium Initiates the Sliding Filament Mechanism • Thick filaments: myosin • Thin filaments: strands of actin molecules • Contraction = formation of cross bridges between thin & thick filaments

  11. Calcium Initiates the Sliding Filament Mechanism (cont.) Figure 6.7

  12. Mechanism of Muscle Contraction: • Calcium released from sarcoplasmic reticulum • Calcium binds to troponin • Troponin-tropomysin complex shifts position • Myosin binding site exposed • Myosin heads form cross-bridges with actin • Actin filaments pulled toward center of sarcomere

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

  14. 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

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

  16. Activity of Muscles Can Vary • Isotonic contractions: muscle shortens, movement occurs • Isometric contractions: muscle doesn’t shorten, no movement • Degree of nerve activation influences force • Terms to know: • Motor unit • Muscle tension • All-or-none principle • Muscle tone

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

  18. Muscle Activity: Slow Twitch vs. Fast Twitch Fibers • Slow twitch muscles: endurance, long duration contraction, contains myoglobin • E.g. Jogging, swimming, biking • Fast twitch: strength, white muscle, short duration contraction • E.g. 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 & Smooth Muscles: • Activation of cardiac and smooth muscles • Involuntary • Specialized adaptations in each • Speed and sustainability of contractions 3. Arrangement of myosin and actin filaments

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

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