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Flashcards in Stretch/Spinal Reflexes Deck (11)
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3 Characteristics of Reflexes



Nuclear Bag vs. Chain Fibers

Nuclei clumped together in middle vs. spread out along fiber


Group IA vs. II Fibers

Wrap around middle (usually bag) vs. around whole thing (usually chain)
Phasic, report change of length vs. tonic, report length


Myotatic (Tendon Tap Reflex)

Stretch in muscle, IA fibers from MSO depol, send through DRG to synapse in spinal cord to alpha neuron to stimulate contraction of that muscle. Primary afferent fibers attached to MSO also form weaker synapses w/ synergistic muscles and excite inhibitory interneurons to antagonist muscles


Gamma Motor Neurons

Located next to alphas in spinal cord, cause muscle spindle to contract w/ muscle to keep sensory part at same length


Normal Muscle Tone

Determined by resting output of gamma motor neurons


Gamma Loop/Alpha-Gamma coactivation

Descending inputs control gamma motor firing to bring to intended length, meaning MSO fires until muscle reaches that length. Afferents keep activating alpha motor neurons until there


Golgi tendon organs

In series w/ fibers in tendons, only responds to muscle contraction. 1b fibers send info back and inhibit homonymous/synergist muscles and activate antagonist muscle to prevent overcontraction and damaging. Not stretched from passive stretch, that's absorbed by muscle fibers


Joint Receptors

Actually in ligaments and capsules and provide proprioceptive information, and cobine w/ signals from MSO, Golgi tendon organs, and skin Rs


Withdrawal Reflex

Painful stimulus travels up nociceptor afferent (III, C, or Adelta), and synapses in spinal cord to activate flexor, inhibit extensor, and do opposite on contralateral side to shift weight (if applicable)


Delay Loop

For walking. Descending signals come down to both sides, one excitatory innervated first and starts walking and synapses w/ inhibitory interneuron that inhibits opposite excitatory interneuron, but also has a self-inhibiting loop that causes it to inhibit itself a little later so that opposite e.i. can do the same thing just afterwards