part 7b4
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part 7b4

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part 7b4 part 7b4 Presentation Transcript

  • Whole-Muscle Contraction
    • whole muscles are made up of many muscle fibers organized into motor units.
    • All the muscle fibers in a single motor unit are of the same fiber type.
    • fiber type designation to the motor unit and refer to
    • slow-oxidative motor units
    • fast-oxidative motor unit
    • fast glycolytic motor units.
    • Depending on the proportions of the fiber types present, muscles can differ considerably in their maximal contraction speed, strength, and fatigability
    • Eg. the muscles of the back and legs, muscles in the arms
  • Control of Muscle Tension
    • The total tension a muscle can develop depends upon two factors:
    • the amount of tension developed by each fiber.
    • the number of fibers contracting at any time.
  •  
    • By controlling these two factors, the nervous system controls whole-muscle tension, as well as the shortening velocity.
    • The number of fibers contracting at any time depends
    • the number of fibers in each motor unit (motor unit size),
    • the number of active motor units.
    • Motor unit size varies considerably from one muscle to another.
    • The force produced by a single fiber, as we have seen earlier, depends in part on the fiber diameter— the greater the diameter, the greater the force.
    • The process of increasing the number of motor units that are active in a muscle at any given time is called recruitment.
    • achieved by increasing the excitatory synaptic input to the motor neurons
    • The greater the number of active motor neurons, the more motor units recruited, and the greater the muscle tension.
    • Motor neuron size plays an important role in the recruitment of motor units.
  • Control of Shortening Velocity
    • the velocity at which a single muscle fiber shortens is determined by:
    • the load on the fiber
    • whether the fiber is a fast fiber or a slow fiber.
    • Translated to a whole muscle, these characteristics become:
    • the load on the whole muscle
    • the types of motor units in the muscle