Neuro Exam 4 (DTR & GTO) – Flashcards
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Deep Tendon Reflex (DTR)
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contraction of agonistic & synergistic mm following the stretching of agonistic mm.
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DTRs - clinically
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hitting the tendon stretches it and subsequently stretches the muscle which contracts
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What is the general function of DTRs?
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maintain muscle tone and upright posture. (gravity alone will cause muscle to stretch, so it contracts creating muscle tone)
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What is the afferent component of the DTR pathway?
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sensory receptor organ
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What is the efferent component of the DTR pathway?
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alpha motor neuron (LMN)
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What happens when the DTR is activated?
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signal travels to dorsal root to then synapse w/ LMN that returns to same mm that was stretched
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What is a muscle spindle?
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• neuromuscular bundle - mechanoreceptor • 3-4 mm long; spindle shaped • consists of a capsule encasing 2-12 intrafusal fibers
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What is an extrafusal fiber?
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normal skeletal m
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What is an intrafusal fiber?
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modified striated skeletal m cells (extrafusal fibers)
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What are the types of intrafusal fibers?
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dynamic nuclear bag (Ia) **(primary funciton) static nuclear bag (II) nuclear chain fiber (II)
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What are muscle spindles & their intrafusal fibers? (ie. function)
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mechanical stretch receptors
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What do the intrafusal fibers measure?
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differentiate between static & dynamic change in (rate of change in) length of the extrafusal fibers
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What type of fibers do DTRs activate?
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Type Ia
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What type of fibers do GTOs activate?
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Type Ib
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DTRs and GTOs are both classified as what type of reflex?
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proprioceptive
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What does the sensory receptor organ measure? (DTR)
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(rate of change in) length of extrafusal fibers
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What is the non-contractile portion of the sensory receptor organ? (DTR)
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annulospiral ending
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What is an Annulospiral Ending?
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receptor organ for type Ia fiber (ie. dynamic nuclear bag)
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What is the primary sensory ending for a sk. m.?
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Ia fibers w/ their annulospiral endings
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Where is the Annulospiral Ending located?
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wrapped around the non-contractile portion
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What does the Ia fiber do for the sensory receptor organ? (DTR)
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**proprioceptive 1st order sensory n (physiologically - Ia) in dorsal column pathway that synapses in medulla w/ 2nd order
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Where is the contractile portion located?
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either end of non-contractile portion
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What are flower spray endings?
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secondary endings (for sk. m.), wrapped around contractile portion.
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What intrafusal fibers are attached to flower spray endings?
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static nuclear bag & nuclear chain fiber
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Discuss the synapse for the Type 1a (Annulospiral Endings)...
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monosynaptically synapse in the SC w/ alpha motor nn (LMN) which innervate homonymous mm (same) or heteronymous m (synergistic)
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Define: Monosynaptically
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only synapse once; no interneuron involved
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What do the Type 1a afferent fibers and alpha motors neurons synapse with to inhibit the antagonist m.?
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Renshaw cells
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What is Reciprocal Inhibition?
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NS modifies itself. antagonist has to relax, otherwise get spasticity
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Discuss the synapse for the Type II fibers (flower spray endings)...
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only synapse (monosynaptically) with alpha motor neurons of only homonymous muscles (extrafusal).
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Where are the cell bodies for the alpha motor neurons located?
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ventral horns
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What do Alpha motor neurons innervate?
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extrafusal fibers of skeletal mm
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What do Alpha motor neurons do?
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activate skeletal mm to contract which produces movement & mm tone
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What are Renshaw cells?
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inhibitory neurons in the gray matter of the SC & are associated w/ alpha motor neuron; they choose to inhibit 1 m & excite 1 m
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What is the GTO (Golgi Tendon Organ) Reflex?
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encapsulated receptor at the junction btwn the m & tendon.
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How are GTOs arranged?
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• separately, in a series • muscle spindles are parallel
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What does the GTO (Golgi Tendon Organ) Reflex measure?
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(rate of change) tension in tendon
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What does the GTO (Golgi Tendon Organ) Reflex do?
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adjust m activity in concert w/ info from m spindle & descending controls (supraspinal input)
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Functionally, Why are GTOs important?
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prevent the tearing of m by inhibiting the contraction of a m being excessively stretched or contracted
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Reciprocal Inhibition is associated with which reflex?
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DTR
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Autogenic Inhibition is associated with which reflex?
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GTO
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Autogenic inhibition aka reverse myotactic reflex:
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type Ib synapse in SC w/ inhibitory interneurons so the muscle relaxes/ gives way - causes a loss of mm tone and sometimes functionally gives way
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What if GTO isn't fast enough?
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traumatic tear, like achilles or gastroc
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When might the GTO not be fast enough?
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when trying to maximize an activity (ie. jumping)
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Stretch Reflex is involved in...
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establishing m tone: gravity stretches mm causing them to contract which creates m tone.
