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IN THE NAME OF ALLAH MOTOR UNITS

IN THE NAME OF ALLAH MOTOR UNITS. Motor units. Definition: A motor unit is defined as a single motoneuron and the muscle fibers that it innervates. The number of muscle fibers innervated can vary from a few fibers to thousands of fibers, depending on the nature of the motor activity.

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IN THE NAME OF ALLAH MOTOR UNITS

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  1. IN THE NAME OF ALLAH MOTOR UNITS

  2. Motor units Definition: A motor unit is defined as a single motoneuron and the muscle fibers that it innervates. The number of muscle fibers innervated can vary from a few fibers to thousands of fibers, depending on the nature of the motor activity.

  3. For eye movements requiring fine control, motoneurons innervate only a few muscle fibers. • For postural muscles involved in large movements, motoneurons innervate thousands of muscle fibers. • A motoneuron pool is the set of motoneurons innervating fibers within the same muscle.

  4. The force of contraction of a muscle is graded by recruitment of motor units(size principle) . • For example, small motoneurons innervate a few muscle fibers, and, because they have the lowest thresholds, they fire first. Small motoneurons also generate the smallest amounts of force. • large motoneurons innervate many muscle fibers. They have the highest thresholds to fire action potentials; thus, they fire last. large motoneurons also generate the greatest amounts of force. • The size principle states that as more motor units are recruited, progressively larger motoneurons are involved and greater tension will be generated.

  5. Types of Motoneurons There are two types of motoneurons: • α motoneurons • γ motoneurons.

  6. α Motoneurons innervate extrafusal skeletal muscle fibers. • Action potentials in α motoneurons lead to action potentials in the extrafusal muscle fibers they innervate, which results in contraction .

  7. γ Motoneuronsinnervate specialized intrafusal muscle fibers, a component of the muscle spindles. • The overall function of the muscle spindle is to sense muscle length; the function of the γ motoneurons innervating them is to adjust the sensitivity of the muscle spindles (so they respond appropriately as the extrafusal fibers contract and shorten).

  8. α Motoneurons and γ motoneurons are coactivated (activated simultaneously) ,so that muscle spindles remain sensitive to changes in muscle length even as the muscle contracts and shortens.

  9. DONE BY: Abdullah Hussain AlMuhaya (430102848) The supervision of Dr: Abdulaziz AlShaiban

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