Ch 3: Clinical Correlates pg 66-73

Question 1

LMNs in the spinal cord that innervate axial muscles are ___ to motor neurons that innervate muscles in the limbs.

Answer 1

medial

Question 2

LMNs in the spinal cord that innervate flexor muscles ____ to motor neurons that innervate extensor muscles.

Answer 2

dorsal

Question 3

generally, LMNs are on the ___ side of the muscles they innervate versus UMNs cell bodies are on the ___ side of the midline than the LMNs they innervate.

Answer 3

ipsilateral

contralateral

Question 4

contractions of skeletal muscles generated by reflexes do not require input from ____ motor neurons

Answer 4

upper

Question 5

what afferent fibers are most important in muscle stretch reflex?

Answer 5

class Ia and II

• both innervate muscle spindle/intrafusal fibers
• class Ia respond to length and rate of stretch
• class II respond only when muscle being stretched
• ->cause stretched muscle to contract
• ->collaterals inhibit antagonist muscle

Question 6

biceps brachii muscle stretch reflex uses what spinal cord segments?

Answer 6

C5 and C6

Question 7

triceps brachii muscle stretch reflex uses what spinal cord segments?

Answer 7

C7 and C8

Question 8

quadriceps femoris (patellar or knee jerk) reflex uses what spinal cord segments?

Answer 8

L3 and L4

Question 9

gastrocnemius/soleus (achilles tendon/ankle jerk) reflex uses what spinal cord segments?

Answer 9

S1 and S2

Question 10

muscle stretch reflexes are graded from 0 which is __ to 4 which is __. A grade of what is normal, moderately brisk reflexes?

Answer 10

0= absence
4= hyperactive with clonus
2+= normal, moderately brisk reflexes

Question 11

muscle strength grading ranges from 0 which is __ to 5 which is __.

Answer 11

0=unable to generate contractions that produce movement

5=normal; generates movement against full resistance

Question 12

what afferent fibers are most important in the Golgi tendon reflex?

Answer 12

class Ib

• innervate GTOs and respond to changes in muscle force/tension
• ->synapse with interneurons to inhibit alpha neurons to muscle generating excessive force (activated muscle relaxed)
• ->collaterals synapse with interneurons to activate alpha neurons of antagonist muscle

Question 13

what is the mechanism of the clasp knife reflex?

Answer 13

activated when muscle is stretched during isometric contraction causing rapid buildup of force–>large discharge by GTOs and Ib afferents–>sudden inhibition/lack of resistance of affected muscle

*enough force that eventually there is a rapid decrease in resistance like a clasp knife closing

Question 14

when can clasp knife reflex be seen?

Answer 14

weight lifters when attempting to lift very heavy load

hyperactive clasp knife reflex in UMN lesions

Question 15

what motor neurons provide efferent innervation to muscle spindles, but not to GTOs?

Answer 15

gamma motor neurons

Question 16

what is the importance of the alpha-gamma coactivation?

Answer 16

when muscles contract, muscle spindles are kept active by gamma motor neurons that contract their polar regions to stretch central region, activate Ia fibers and increase firing of alpha motor neurons

Question 17

Renshaw cells?

Answer 17

inhibitory interneurons that provide recurrent inhibition to alpha motor neurons

Question 18

how does tetanus toxin work in regards to Renshaw cells?

Answer 18

prevents release of glycine from Renshaw cells–>patients have sustained contractions and spasms ex. lockjaw

Question 19

what afferent fibers are important in flexor withdrawal/crossed extensor reflex?

Answer 19

A-delta and C dorsal root fibers

• enter in lateral division of dorsal root
• will cause contraction of flexor muscle on side of stimulus and extensors of opposite limb for postural support