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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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Muscular system l.jpg

Muscular System

Chp. 6


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The Muscular System is very complex:

Figure 6.2


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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


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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


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Skeletal Muscle Contractile Unit:

  • Single muscle cell contains many myofibrils:

    • ea myofibril is composed of sacromeres

    • actin filaments

    • myosin filaments

    • z-lines


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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


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Skeletal Muscle Contractile Unit (cont.)

Figure 6.5


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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


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Nerve Activation of Individual Muscle Cells (cont.)

Figure 6.6


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Calcium Initiates the Sliding Filament Mechanism

  • Thick filaments: myosin

  • Thin filaments: strands of actin molecules

  • Contraction = formation of cross bridges between thin & thick filaments


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Calcium Initiates the Sliding Filament Mechanism (cont.)

Figure 6.7


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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


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Mechanism of Muscle Contraction (cont.)

Figure 6.8


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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


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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


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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


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Muscle Contraction: Myogram

  • Latent period

  • Contraction

  • Relaxation

  • Summation vs. tetanus

Figure 6.10


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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


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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


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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


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Diseases and Disorders of the Muscular System

  • Muscular dystrophy

  • Tetanus

  • Muscle cramps

  • Pulled muscles

  • Fasciitis


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