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27 Cards in this Set
- Front
- Back
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stretch reflex is aka |
myotatic reflex |
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myotatic |
key for posture monosynaptic *Max convergence and divergence of thispathway *Changes in stretch reflex are involved inactions commanded by the brain * Each 1a fiber will contact virtually all alpha motor neurons, and each alpha get input from EVERY spindle in that muscle |
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•Phasic stretch reflex occurs in response torapid, transient stretch of the muscle (reflex hammer) *1a* |
•or by an unexpected impediment to an ongoing movement |
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•Tonic stretch reflex occurs in response to a sloweror steady stretch applied to a muscle |
True |
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Phasic(or 1a) Stretch Reflex |
•Elicited by the primary(1a) endings of muscle spindles |
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Phasic Stretch Reflex |
•excitatory (+) synapses directly (mono-synaptically) on virtually all a motor neurons that supply the same (homonymus) muscle and with many of its synergistic muscles
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**1a: donot contact the gamma motor neurons: to avoid a positive-feed back loop ! ** |
In all other cases, excitation causes contraction |
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1a fibers can end on a variety of interneurons |
reciprocal 1a inhibitory neuron innervates antagonist muscles |
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Monosynaptic nature |
little opportunity for direct control ofactivity through this reflex arc BUT * CNS overcomes this problem by controllingmuscle spindle sensitivity via the g motor neuron system* |
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knee reflex- stretch muscle spindle |
AP enters spinal cord and joins at dorsal column pathway. Other branch synapses with motor neurons in ventral horn inhibiting flexors and activating extensors |
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Tonic Stretch Reflex |
elicited by passivelybending a joint |
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Tonic Stretch Reflex |
circuit includes both group 1a and II afferent fibers frommuscle spindles group II= monosynaptic connections with alpha motor neurons and excite through di/polysynaptic pathways |
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Howis muscle tone innervated? ** Test question |
Normally there is ongoing activity in the 1a and IIafferents and help maintain a baseline firing rate of alpha motor neurons. Therefore tonic stretch reflexes contributes to muscle tone. Activity also contributes to posture maintenance |
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soldier standing |
tonic stretch elicited to maintain posture. •If the muscle length is ↑, then there is an ↑ group 1a and II firing to cause contraction to reverse stretch |
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•Passive shortening of the muscle will unload the spindle which .... |
↓ excitatory drive to the motor neurons and thus relaxation of the muscle |
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stretch reflex is essentially a |
feedback system to regulate muscle length |
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Hyperactive stretch reflex can lead totremors and clonus EXAM Question. What is clonus |
•Clonus is a series of involuntary,rhythmic, muscular contractions and relaxations |
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Inverse Myotatic or 1b Reflex |
•Feedback system to help maintainforce levels in a muscle •Afferent 1b fibers branch as they enter the spinal cord and end on 2 interneurons Receptor organ are GTO •There are no mono-synaptic connections to a motor neurons |
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2 interneurons afferent 1b end on |
•Interneurons that inhibit a motor neurons that supply the homonymus muscle •excitatory interneurons that activate a motor neurons to the antagonistic muscle |
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2 synapses in series |
disynaptic reflex arc |
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1b activity should have the opposite action of the 1a stretch reflex |
EXAM- what is the difference in mono and disynaptic |
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Arm lifting bicep and weight is too much, bicep drops |
GTOs detect excessive force and discharge action potentials --> spinal cord inhibitory neurons --> turn off motor neurons to the biceps and to other flexors synergistic to thebiceps and turn on motor neurons to the extensors that are antagonistic to the biceps to extend the arm and thebarbell drops |
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1a and 1b synergy |
maintain posture muscles fatiguing- coordinated action of both musclespindles and GTO |
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Afferent volleys |
•excitatory inter-neurons to activate the a motor neurons that supply the flexor muscles in the ipsilateral limb •inhibitory interneurons to inhibit thea motor neurons that supply the antagonistic extensor muscles |
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•Collaterals of interneurons (Commissural) cross the midline to excite contralateral extensor motor neurons and inhibit flexors |
Results in extension of the opposite limb (Crossed extension Reflex) |
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•Collectively the spinal reflexes provide for stability and postural support (the myotatic and inverse myotatic) and mobility (flexor withdrawal) |
true |
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•Central Pattern Generator (CPG) |
a set of neurons and circuits capable of generating the rhythmic activity that underlies motor acts, locomotion. (cat with brainstem cut) |
