Stretch/Spinal Reflexes

Question 1

3 Characteristics of Reflexes

Answer 1

Rapid
Involuntary
Stereotypic

Question 2

Nuclear Bag vs. Chain Fibers

Answer 2

Nuclei clumped together in middle vs. spread out along fiber

Question 3

Group IA vs. II Fibers

Answer 3

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

Question 4

Myotatic (Tendon Tap Reflex)

Answer 4

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

Question 5

Gamma Motor Neurons

Answer 5

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

Question 6

Normal Muscle Tone

Answer 6

Determined by resting output of gamma motor neurons

Question 7

Gamma Loop/Alpha-Gamma coactivation

Answer 7

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

Question 8

Golgi tendon organs

Answer 8

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

Question 9

Joint Receptors

Answer 9

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

Question 10

Withdrawal Reflex

Answer 10

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)

Question 11

Delay Loop

Answer 11

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