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part 7b4

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