Babinski reflex and corticospinal tract lesion

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Muscle SpindlesOrganizationGamma motor neurons innervate the intrafusal muscle fibers.Activation ofgamma neuronsShortening of the polar regionsof the intrafusal fibersStretches the noncontractilecenter regionsIncrease firing of thesensory endingsTherefore, the gamma motor neurons provide amechanism for adjusting the sensitivity of the musclespindles.2 types of motor fibers•Static gamma motor neuron – innervate both staticbag and chain fibers•Dynamic gamma motor neuron – innervate onlydynamic bag fibers5Gamma motor neurons: Static and Dynamic ResponsesIa sensory fiber responseStretch alone: small dynamic response to musclestretch, a moderate increase in steady-state firing.Static gamma motor neuron stimulated: steady-stateresponse increase, dynamic response decrease.Dynamic gamma motor neuron stimulated: dynamicresponse markedly enhanced, steady-state responsegradually returns to original level.Increase in activity of dynamic gamma motor neuronsincrease the dynamic sensitivity of the type Ia endingsbut have no influence on the type II endings.Increase in activity of static gamma motor neuronsincrease the tonic level of activity in both the type Ia andII endings, decrease the dynamic sensitivity of type Iaendings.6
Activation of gamma MN during active muscle contraction enablesthe muscle spindles to continue sensing changes in muscle length•Activation of the gamma motorneurons leads to contraction of theends of the fibers, which stretch ofthe central regions.•This allows the spindle to respond tochanges in muscle length over a widevariety of lengths. I.e. adjusts thespindle sensitivity•The activation of alpha and gammamotor neurons together enable themuscle spindle to respond duringlong contractions.•Alpha and gamma MN are activatedtogether during voluntarymovements.(alpha-gammacoactivation)7The Alpha-Gamma Co-activationDescendingPathwaysIncrease in gammaMN firingIncrease in IafiringIncrease in alphaMN firingIncreased MuscleContraction8
Page 1 and 2: Babinski reflex and corticospinal t
Page 3: Muscle SpindlesIntrafusal musclefib
Page 7 and 8: Summary of Sensory FibersIa•Goes
Page 9: Functions of the Ia inhibitory inte

Babinski reflex and corticospinal tract lesion

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