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NEUROPHYSIOLOGY

Proprioception and Reflex Palhways: III

Ib fi bers

Extrafusul musde fiber

Intrafusal muscle tiber

Alpha motor ne urons

Gamma motor neurons

Golgi

tendon

A. Passbe stretch. Both intrafusal and extrafu$al muscle fibers stretched; spindles actbaled. Kufle* via la flbers and alpba motor neurons causes secondary contraction (hasis of stretch reftexes, soch as knee ierkj. Stretch is too weak to acthrate Golgi tendon organs

Ib fibers + -t- • *    . ,

_._ • •>.    i A nh.i .ifHvAtion

la fibers

Extratusal muscle fiber Intrafusal musde tiber

Inhibitory inlerneuron ■

Alpha motor neurons

Gamma motor neurons

Golgi

B. Actbe contraction. C entral excitation of alpha motor neurons only causes contraction of extrafusal musde fibers vsith c<msequent relaxation of intrafusal flbers; spindles not actbated Tension is Iow; <loes oot adjust to incrcased resistance Tendon organ actbated, causing relaxation

" Alpha and i gamma actbation

Ib fibers

Extrafusal musde fiber

J Intrafusal musde fiber

Gamma motor neurons

Golgi

tendon

C. Actbe contraction with gamma coactKation. Intrafusal as well a« extrafusal fibers contract; spindles actbated, reinforcing contraction stimulus via la tihers in arrord with resistance Tendon organ actbated. causing relaxation ir load is too great

Figurę 2.27 Proprioceptive Refiex Control of Muscle Tension_

Interaction of the muscle Splndle and Golgi tendon organ dunng passive stretch of a muscle (panel A) and during a contraction ipanels B and

C}.

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