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16 Somatosensory Receptors

P group ii afferents wrapped around other fibers wo

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Unformatted text preview: = a.p. - Group II afferents wrapped around other fibers w/o spindle shape: known as nuclear Somatosensory Receptors chain fibers, not nuclear bag fibers (don't need to know this) October 20, October 20, 20 Gamma-motoneuron Intrafusal fibers are innervated by -motor motor axons motoneuron discharge increases tension within spindle increased sensitivity to stretch of muscle Gamma ()-motoneuron - Gamma motor efferent axons: innervate intrafusal fibers - Cause them to tighten up and sensitize - Motoneuron discharge: spindle tension = sensitivity to muscle stretch 6 - Group II afferents can arise from same fibers as Ia afferents - Found to side, not in spindle-shaped region - Apply stretch: activate Ia endings = sustained response - But if muscle contracted: remove tension from intrafusal fiber - Contraction caused by large motoneurons ( motor efferents: go to extrafusal fibers outside spindle = cause muscle contraction) - If apply stretch: initially no response in muscle spindle - To keep intrafusal fiber sensitive at all diff lengths: use gamma efferents to keep spindle always tight = always sensitive = just on the verge of discharge 3 of 5 Somatosensory Receptors October 20, 2010 PSL302Y: Lecture 15, by Prof. MacKay# Wed., Oct.20, 2010...
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