Skeletal muscle phys

  1. Define motor unit and muscle twitch and describe the events occurring during the three phases of a muscle twitch.

    motor neuron and muscle cells it innervates

    twitch: max level of force bc calcium saturation

    form tetanus in muscle after increased frequency

    • single action potential gives twitch

      • refractory: delay from Electrochem coupling and beginning crossbridge formation

      • force development: crossbridge cycling

      • force relaxation: calcium pumped back into sr preventing cycling

  2. Explain how smooth, graded contractions of a skeletal muscle are produced.

  3. Differentiate between isometric and isotonic muscle actions and types of isotonic actions.

    • isometric: no change in length, max force

      • determined by stimulation freq, sarcomere length, cross sectional area

    • isotonic: constant change in length/speed via action

      • concentric: shortening

      • eccentric: lengthening

  4. Describe the force-velocity curve and its X and Y intercepts and the power curve.

    • y is force, x is shortening

    max velocity: cant generate much force

    power = force x speed

    isometric: max force

  5. Describe factors that influence the force, velocity, and duration of skeletal muscle action.

    • inc freq - max thin filament active - max crossbridge cycl

    • myosin type (isoform) determines max atpase rate - crossbridge cycl rate

    • high speed: fast myosin isoforms

    • slow speed: slow myosin isoform

  6. Define lever and explain how a lever operating at a force advantage differs from one operating at a speed advantage.

    most often: second class

    • fulcrum/pivot; joint

    • load/resist: item moved

    • effort/force: result of action

    • force advantage: short distance between load and fulcrum, long between effort and fulcrum

    • speed advantage: long distance between load and fulcrum short between effort and fulcrum

  7. Name the three types of lever systems and indicate the arrangement of effort, fulcrum, and load in each. Also note the advantages of each type of lever system.

    strap like: origin to insert

    pinate: angled fibers, cross section diameter

    • first class

      • fulcrum between load and effort

    • second class

      • fulcrum one end, effort at other, load between

    • third class: load at one end, fulcrum at other, effort between load and fulcrum

  8. Explain how the multicellular organization of muscle fibers in a muscle organ influences its musculoskeletal action (speed vs force).

    • low cross sec area = low force

    • more sarcomeres = high extent of shortening

    • high cross sec = high force

    • fewer sarcomeres = low extent of shortening

  9. Identify and name the function of select muscles of the head.