Spinal mechanisms of motor control

Question 1

where is the muscle spindle located?

Answer 1

parallel to extrafusal muscle fibers

Question 2

where is the golgi tendon organ located?

Answer 2

in series with muscle

Question 3

which type of neuron innervates intrafusal muscle fibers?

Answer 3

group Ia fiber

Question 4

which neuron is larger - alpha motor neuron or gamma motor neuron?

Answer 4

alpha

Question 5

what is the function of beta motor neurons?

Answer 5

innervation of both extrafusal and intrafusal fibers

Question 6

how does coactivation of alpha and gamma motoneurons work?

Answer 6

gamma motor neurons contract intrafusal fibers while extrafusal fibers are contracted - maintains sensitivity to intrafusal fiber stretch

Question 7

what kind of information is carried by group Ia fibers?

Answer 7

1. how fast the muscle length is changing 2. current length of muscle

Question 8

what kind of information is carried by group II fibers?

Answer 8

only muscle length

Question 9

how dos the gamma motoneuron control muscle spindle response?

Answer 9

senses sensitivity and provides fusimotor drive to muscle spindles

Question 10

how does the phasic (DTR) stretch reflex work?

Answer 10

Ia axon from stretch receptor synapses on alpha motor neuron of homonymous muscle as well as an inhibitory interneuron for antagonist muscle

Question 11

how are phasic stretch reflexes tested?

Answer 11

tendon tap

Question 12

how are tonic stretch reflexes tested?

Answer 12

passive flexion or extension of a muscle at various speeds

Question 13

how is reciprocal innervation in the spinal cord related to the stretch reflex?

Answer 13

1. group Ia fibers excite homonymous muscle and synergists 2. group Ia fiber collaterals end on Ia inhibitory interneurons, inhibiting alpha motor neurons of antagonist muscles

Question 14

definition: co-contraction

Answer 14

both the prime mover at a joint and its antagonists are contracted simultaneously - stiffens the joint

Question 15

when is co-contraction used?

Answer 15

precision movements and joint stabilization

Question 16

what is the normal group Ib reflex?

Answer 16

innervation of GTO

Question 17

when does the clasp knife response occur?

Answer 17

hyperactive stretch reflexes of the spastic patient causes increase in resistance to stretch, followed by a sudden decrease

Question 18

definition: reciprocal innervation

Answer 18

reciprocal innervation causes Ia fiber from muscle spindle of homonymous agonist muscle to inhibit the antagonist muscle via the Ia inhibitory interneuron - yields reciprocal inhibition

Question 19

what is the sensory organ for the phasic stretch reflex?

Answer 19

muscle spindle

Question 20

how does the tonic stretch reflex work? what does it measure?

Answer 20

1. Ia fibers fires more during lengthening - depends on both primary and secondary endings 2. Ia fibers go to both homonymous muscles and synergist muscles 3. measures muscle tone

Question 21

what is the GTO (group Ib) reflex arc?

Answer 21

1. increased tension on muscle increases Ib firing rate 2. Ib fiber synapses on Ib inhibitory interneuron - inhibits alpha motor neuron of homonymous muscle 3. can be modified by higher brain centers

Question 22

what are the roles of the Renshaw cell?

Answer 22

1. can produce recurrent inhibition in alpha motor neurons of agonist muscle 2. can inhibit Ia inhibitory interneurons to antagonist muscles 3. allows co-contraction at a joint