motor reflex

Question 1

what is the purpose of the myotatic reflex

Answer 1

protect muscle from excessive stretch

Question 2

what structure initiates the myotatic reflex

Answer 2

muscle spindle/intrafusal fibers

Question 3

are intrafusal fibers motor or sensory

Answer 3

both

Question 4

what are the two sensory fibers of the intrafusal fibers/muscle spindle

Answer 4

nuclear bag fiber

nuclear chain fiber

Question 5

what is the structure of the primary afferent fiber of the muscle spindle

Answer 5

large, myelinated Ia fiber

Question 6

does the primary afferent fiber of the muscle spindle innervate the nuclear bag or the nuclear chain fiber

Answer 6

both

Question 7

what does the primary afferent fiber of the muscle spindle detect

Answer 7

length of muscle

rate of change of muscle length

Question 8

what is the structure of the secondary afferent fiber of the muscle spindle

Answer 8

smaller myelinated group II fiber

Question 9

does the secondary afferent fiber of the muscle spindle innervate the nuclear bag or the nuclear chain fiber

Answer 9

only nuclear chain

Question 10

what does the secondary afferent fiber of the muscle spindle detect

Answer 10

length of muscle

Question 11

what innervated the motor portion of the intrafusal fiber

Answer 11

gamma motor neuron!

Question 12

what does the motor portion of the intrafusal fiber/muscle spindle do

Answer 12

control the length of the sensory portion of the muscle spindle

Question 13

when intrafusal muscle contracts, what happens to the sensory intrafusal fibers

Answer 13

they stretch and become more sensitive to further stretch

Question 14

how do the sensory intrafusal fibers initiate motor reflexes

Answer 14

the IA (primary) afferent fiber synapses on the alpha motor neuron of the stretched muscle

Question 15

what action does the primary afferent fiber have on the antagonist muscle

Answer 15

it inhibits the motor neuron of the antagonist muscle => relaxation

Question 16

what is the purpose of the golgi tendon reflex

Answer 16

protect muscle from damage caused by excessive force

Question 17

where is the structure that initiates the golgi tendon reflex found

Answer 17

golgi tendon organ is found extending from SC => muscle tendon

Question 18

what is the golgi tendon organ

Answer 18

Ib bare nerve ending with lots of branches

Question 19

how does the golgi tendon organ protect muscle

Answer 19

it produces APs which increase in intensity with increased tension and activate an inhibitory interneuron

Question 20

what causes the AP intensity to of the GTO to go back to baseline

Answer 20

relaxation of the muscle

Question 21

what are the two mechanisms underlying the return of reflexes in spinal shock

Answer 21

• axonal sprouting below transection

- expression of self-activating receptors

Question 22

what is the cause of rigidity

Answer 22

continual activation of alpha motor neurons by the brainstem => maintained muscle contraction

Question 23

what is the cause of spasticity

Answer 23

continual activation of gamma motor neurons => hyperactive myotatic reflex

Question 24

what structure activates gamma motor neurons

Answer 24

brainstem facilitatory region

Question 25

what does the brainstem inhibitory region do

Answer 25

inhibit gamma motor neurons => muscle spindle is less sensitive to stretch

Question 26

which of the brainstem regions ((+)/(-) requires activation by the cortex

Answer 26

brainstem inhibitory region

Question 27

if a pt comes in with their left limb extended and the arm and wrist flexed, what has probably happened to cause them

Answer 27

stroke in the vicinity of the internal capsule => decorticate posturing