part 7b4

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part 7b4

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

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