Review of reflex arc.. Muscle Stretch Reflex These first two slides have provided a brief outline of...
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Transcript of Review of reflex arc.. Muscle Stretch Reflex These first two slides have provided a brief outline of...
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.
The 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.
• This has been a brief description of the muscle stretch reflex arc and how it operates.
• The next series of slides will demonstrate how the muscle stretch reflex arc, the intrafusal muscle fibers, and the gamma efferent neurons are used in local control of muscle fibers.
Review: what happens when the stretch receptor is stretched? Notice the change
in frequency of action potentials.
What events will stretch the stretch receptor?
• Stretch of the entire muscle (tap the patellar tendon, watch the foot jerk!)
What events will stretch the stretch receptor?
• Stretch of the entire muscle (tap the patellar tendon, watch the foot jerk!)
OR
What events will stretch the stretch receptor?
• 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 receptor?
• 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?
What events will stretch the stretch receptor?
• 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.
• This seems like a stupid thing to do because it would be easier just to stimulate the extrafusal muscle fiber with the alpha efferent neuron.
• But look what actually happens:
Both the intrafusal fibers AND the extrafusal fibers contract to the same extent. The stretch receptor doesn’t feel a thing!
It becomes stretched (the muscle doesn’t shorten, remember?) and increases the frequency of action potentials along the stretch receptor afferent…..
…which stimulates only the alpha efferent, causing the extrafusal muscle fiber to generate greater amounts of tension.