PHGY 209 Lecture Notes - Lecture 28: Golgi Tendon Organ, Nuclear Bag Fiber, Intrafusal Muscle Fiber

• School: McGill University
• Department: Physiology
• Course: PHGY 209
• Professor: Ann Wechsler

Document Summary

External load (lyfting), muscles lengthened, increase in muscle spindle afferent activity: muscle spindles like to be stretched out to work properly. Voluntary flexion: in lyfted position (flexed), muscles shortened,, muscle spindle collapses --> sensitivity reduced. Alpha-gamma coactivation: intrafusal fibers contract, to make sure muscle spindle is stretched, ensures muscle spindle works properly, spindle sensitivity is maintained. Alpha motor neuron activity shortens the muscle, so intrafusal fibers have to be activated, contract and maintain muscle spindle elasticity (rubber band) When you activate alpha you are also activating gamma. As alpha activates the extrafusal fibers, causing muscle to contract, gamma activates intrafusal fibers, stretching the muscle fiber so that it doesn"t collapse. Alpha motor neurons lengthen/shorten muscle spindle; muscle spindle works well when stretched. Stretch reflex: mediated by muscle spindle: positive feedback loop. Resists change in muscle length -- this sets muscle tone. Inverse stretch reflex: mediated by golgi tendon organ. Recall: golgi tendon organ is in series with the muscle.