Spinal reflexes

Question 1

which neurons are involved in reflexes?

Answer 1

alpha and gamma motor neurons

Question 2

what do alpha motor neurons innervate?

Answer 2

skeletal muscle fibers (extrafusal fibers)

Question 3

what do gamma motor neurons innervate?

Answer 3

contractile (polar) portion of intrafusal fibers of muscle spindles

Question 4

what forms the sensory (afferent) limb of a reflex arc?

Answer 4

1. pseudounipolar (sensory) neuron whose cell body is housed in a DRG 2. peripheral process is in skin / skeletal muscle / tendon / joint capsule; central process synapses in spinal cord gray matter

Question 5

what forms the motor (efferent) limb of a reflex arc?

Answer 5

1. motor neuron whose cell body is usually located in the ventral horn of the spinal cord 2. axon synapses in skeletal muscle

Question 6

what is the receptor in the muscle stretch reflex?

Answer 6

muscle spindle

Question 7

what is the receptor in reciprocal inhibition?

Answer 7

muscle spindle at peripheral end of 1a fiber

Question 8

what is the receptor in autogenic inhibition?

Answer 8

GTO

Question 9

what is the stimulus in autogenic inhibition?

Answer 9

muscle contraction triggers sensory endings innervating tendons to fire

Question 10

what does autogenic inhibition inhibit?

Answer 10

muscle over-contraction

Question 11

what does the autogenic inhibition reflex protect?

Answer 11

tendon

Question 12

where are the receptors in the flexor reflex (withdrawal reflex, nociceptive reflex)?

Answer 12

cutaneous

Question 13

what type of fibers make up the afferent limb of the flexor reflex (withdrawal reflex, nociceptive reflex)?

Answer 13

lightly myelinated Ad fibers, or unmyelinated C fibers of pseudounipolar neurons whose cell bodies are in a DRG

Question 14

where does the central process of a pseudounipolar neuron involved in the flexor reflex enter the spinal cord?

Answer 14

enters the dorsolateral tract of Lissauer and branches into short ascending and descending fibers

Question 15

what neurons are involved in the crossed extension reflex?

Answer 15

commissural interneurons whose axons cross the midline to synapse with excitatory and inhibitory interneurons located in the ventral horn of the spinal cord on the opposite side

Question 16

gamma motor neurons are under what type of control?

Answer 16

supraspinal (from the brain)

Question 17

what do gamma motor neurons stimulate in maintenance of muscle tone?

Answer 17

polar (contractile) portions of intrafusal fibers

Question 18

what triggers the slight contraction of gross muscle during muscle tone maintenance?

Answer 18

stretch reflex

Question 19

what does stimulation of gamma motor neurons do to muscle tone? inhibition of gamma motor neurons?

Answer 19

1. increase 2. decrease

Question 20

the gamma loop contains what five components?

Answer 20

1. gamma motor neurons 2. intrafusal fibers 3. 1a fibers 4. alpha motor neurons 5. extrafusal fibers

Question 21

what is the purpose of alpha gamma coactivation?

Answer 21

a way to maintaining sensitivity to stretch during gross muscle contraction