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Review of reflex arc. Muscle Stretch Reflex. These first two slides have provided a brief outline of the muscle stretch reflex. You can now go back to the lab exercise. The remainder of this presentation will be used to illustrate Lecture Objective 66.

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These first two slides have provided a brief outline of the muscle stretch reflex. You can now go back to the lab exercise.

The remainder of this presentation will be used to illustrate Lecture Objective 66.



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The example of intrafusal muscle fibers are tiny muscle fibers attached to either end of the stretch receptor. They are innervated by gamma efferent neurons and are not part of the stretch reflex arc.


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D extrafusal muscle fiber e stretch receptor f intrafusal muscle fiber l.jpg
D—extrafusal muscle fiber reflex arc and how it operates.E—stretch receptorF—intrafusal muscle fiber


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A— reflex arc and how it operates.stretch receptor afferent neuron


B alpha efferent neuron this completes the stretch reflex arc l.jpg
B— reflex arc and how it operates.alpha efferent neuronThis completes the stretch reflex arc.


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Review: what happens when the stretch receptor is reflex arc and how it operates.stretched? Notice the change in frequency of action potentials.


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What events will stretch the stretch receptor? reflex arc and how it operates.

  • Stretch of the entire muscle (tap the patellar tendon, watch the foot jerk!)


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What events will stretch the stretch receptor? reflex arc and how it operates.

  • Stretch of the entire muscle (tap the patellar tendon, watch the foot jerk!)

    OR


What events will stretch the stretch receptor13 l.jpg
What events will stretch the stretch receptor? reflex arc and how it operates.

  • Stretch of the entire muscle (tap the patellar tendon, watch the foot jerk!)

    OR

  • Contraction of the intrafusal muscle fiber!


What events will stretch the stretch receptor14 l.jpg
What events will stretch the stretch receptor? reflex arc and how it operates.

  • Stretch of the entire muscle (tap the patellar tendon, watch the foot jerk!)

    OR

  • Contraction of the intrafusal muscle fiber!

    • What would make this happen?


Reminder the intrafusal muscle fibers are innervated by gamma efferent neurons l.jpg
Reminder: reflex arc and how it operates.The intrafusal muscle fibers are innervated by gamma efferent neurons.


What events will stretch the stretch receptor16 l.jpg
What events will stretch the stretch receptor? reflex arc and how it operates.

  • Stretch of the entire muscle (tap the patellar tendon, watch the foot jerk!)

    OR

  • Contraction of the intrafusal muscle fiber!

    • This will occur any time the gamma efferent fiber stimulates the intrafusal muscle fiber.


C gamma efferent neuron to intrafusal muscle fiber l.jpg
C— reflex arc and how it operates.gamma efferent neuron to intrafusal muscle fiber




What if we could stimulate c work through the sequence c f e l.jpg
What if we could stimulate C? Work through the sequence: C reflex arc and how it operates.→ F →E


What if we could stimulate c work through the sequence c f e a l.jpg
What if we could stimulate C? Work through the sequence: C reflex arc and how it operates.→ F →E →A


What if we could stimulate c work through the sequence c f e a b l.jpg
What if we could stimulate C? Work through the sequence: C reflex arc and how it operates.→ F →E →A →B


What if we could stimulate c work through the sequence c f e a b d l.jpg
What if we could stimulate C? Work through the sequence: C reflex arc and how it operates.→ F →E →A →B →D


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Both the intrafusal fibers AND the extrafusal fibers contract to the same extent. The stretch receptor doesn’t feel a thing!



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It becomes stretched (the muscle doesn’t shorten, remember?) and increases the frequency of action potentials along the stretch receptor afferent…..


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…which stimulates only the alpha efferent, causing the extrafusal muscle fiber to generate greater amounts of tension.


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