LECTURE 8
LEVER SYSTEM AND SKELETAL MUSCLE

Learning Goals

1. List four functional properties that distinguish muscle tissue from other tissues, and briefly relate the structural features of muscle to functional properties.

2. Compare and contrast skeletal, cardiac, and smooth muscle tissue. Devise a comparison chart for key characteristics such as location, cell shape, type of innervation, and function.

3. Name the layers of connective tissue that occur in and around a skeletal muscle, and briefly describe a muscle’s blood and nerve supply.

4. Define muscle fascicles.

5. Describe the various ways in which muscles attach to their origins and insertions. Explain attachments of muscles to bones through tendons, aponeuroses, and direct and indirect attachments.

6. Describe and explain the structural and organizational levels of skeletal muscle. Begin with the muscle as an organ followed by the fascicle, muscle fiber, myofibril, and sarcomere, then end with the myofilament; include comments on connective tissues as appropriate.

7. Explain the sliding filament theory of muscle contraction. What is the role of titin?

8. Describe the components of the neuromuscular junction and the innervation of skeletal muscles. Define motor unit.

9. Compare and contrast the three kinds of skeletal muscle fibers: slow oxidative fibers (fatigue-resistant and best for maintaining posture), fast glycolytic fibers (for short bursts of power), and fast oxidative fibers (for long-term production of strong contraction).

10. Explain some symptoms of myofascial pain syndrome and fibromyalgia.

11. Explain the elements of leverage and lever systems in the human body; distinguish between first-class lever, second-class lever, and third-class lever relationships.

12. Explain how muscles are classed into several functional types; give specific muscle examples and describe the functions of prime movers (agonists), antagonists, synergists, and fixators.


I. Our Lever System

a. Mechanics of skeleton as a lever system

  • Terms:

    -Force arm (DF) = distance of force (F) from fulcrum




    -Load arm (DL) = distance of load (L) from fulcrum




  • Relationship:

    (DF)(F) = (DL)(L)











    b. Implication

  • In most lever system in body, the force arm is short = poor mechanical advantage with regard to strength




  • A short force arm amplifies movement = greater range of movements and velocity of movement.





    II. Muscle Action

    a. Prime movers--agonists




    b. Synergists and fixators




    c. Antagonists




    III. Skeletal Muscle

    a. General characteristics

  • Muscle fibers are multinucleated




  • Cannot divide after birth




  • New muscles can form from undifferentiated satellite cells




  • Striated




  • Vascularized and innervated





    b. Gross anatomy--in descending order of organization

  • Muscle




  • Muscle fascicle--bundle of muscle cells




  • Muscle fiber=muscle cell




  • Myofibrils--protein bundles within a muscle cell





    c. Mechanics of contraction

  • Sliding filamant





    d. Energy source

  • ATP




  • Creatine phosphate




  • Glycogen



  • Aerobic to Anaerobic metabolism






    e. Types of skeletal muscle (classified by metabolic activity)

  • Slow oxidative twitch (red muscle)

    -slow




    -aerobic




    -fatigue slowly




  • Fast glycolytic twitch (white muscle)

    -fast




    -anaerobic




    -fatigue quickly




  • Fast oxidative twitch

    -intermediate speed




    -uses both aerobic and anaerobic metabolism




    -intermediate fatigue