functional neuroanatomy of reflexes W4

Question 1

what is a stretch reflex?

Answer 1

the contraction of a muscle in response to its passive stretching

Question 2

what can cause a stretch reflex?

Answer 2

tapping a tendon

Question 3

stretch reflex - neural pathway?

Answer 3

afferent fibre carries signal from stretch receptors in muscle spindles
efferent (a motor neuron) carries signal back to muscle to contract
inhibitory interneuron carries inhibitory signal to antagonist muscle

Question 4

clinical relevance of stretch reflex

Answer 4

relevant in evaluation of patients with weakness
weakness due to upper or lower motor neurons - reflexes help us distinguish these

Question 5

muscle bulk in UMN/LMN pathology?

Answer 5

UMN - normal (atrophy if chronic)
LMN - prominent atrophy early on (may also see fasciculations)

Question 6

tone in UMN/LMN pathology?

Answer 6

UMN - increased (spasticity) +/- ankle clonus
LMN - decreased (flaccid)

Question 7

pattern of weakness in UMN/LMN pathology?

Answer 7

UMN - pyramidal
LMN - selective to affected regions

Question 8

reflexes in UMN/LMN pathology?

Answer 8

UMN - brisk (hyperreflexia)
LMN - reduced/absent

Question 9

plantar response in UMN/LMN pathology?

Answer 9

UMN - upgoing (Babinski sign)
LMN - downgoing/absent

Question 10

UMN lesion - stretch reflex pathology?

Answer 10

normally descending pathways inhibit resting tone and reflexes. in UMN pathology this inhibition is lost, hence spasticity and hyperreflexia

Question 11

hyperreflexia?

Answer 11

pathological brisk reflexes

Question 12

LMN lesion - stretch reflex pathology?

Answer 12

reflexes lost due to damage to motor neuron carrying signal back to muscle
damage to sensory afferent component of reflex will also diminish reflexes

Question 13

which spinal level does reflexes tested in the upper limbs represent?

Answer 13

biceps - C5
triceps - C7
supinator - C6

Question 14

what spinal level does reflexes tested in the lower limb represent?

Answer 14

knee or patellar tendon - L3-L4
ankle - S1

Question 15

flexor reflex neural pathway

Answer 15

cutaneous afferent neuron (nociceptive) carries pain signal to spine.
signal carried to both legs via interneuron
ipsilateral flexors activated (withdraws leg)
contralateral extensors activated (supports weight)

Question 16

Babinski response?

Answer 16

minor stimulus to sole causes abnormal flexion response (due to loss of descending influences which normally limit this reflex)

Question 17

plantar response?

Answer 17

blunt object run along lateral sole of foot
normal responses: great toe moves downward, other toes may curl, nothing happens, whole foot withdraws

abnormal responses: great toe upgoing (sign of UMN pathology)

Question 18

true Babinski sign?

Answer 18

upgoing toe plus flexion of leg muscles