Blink Reflex

Question 1

Draw and explain the anatomical pathway and define the R1 and R2 locations on the picture.

Answer 1

The afferent loop of the blink reflex is mediated by the 1st division of the trigeminal nerve (V1), which synapses with both the main sensory nucleus of cranial nerve V (Vm) in the midpons and nucleus of the spinal tract of CN V (Vs) in the medulla. The earlier R1 potential is mediated by a disynaptic connection between the main sensory nucleus and the ipsilateral facial motor nucleus (VII). The later R2 responses are mediated by a mulisynaptic pathway between the nucleus of the spinal tract of CNV and both ipsilateral and contralateral facial nuclei (VII). The efferent pathway for both R1 and R2 is mediated via the facial nerve to the orbicularis oculi mms.

Question 2

Explain each set of waveforms working back in the drawing of the anatomical pathway of the blink reflex and identify the location of the lesion.

Answer 2

A- normal

B- Incomplete R trigeminal nerve lesion

C- Complete R trigeminal lesion

D- Incomplete R facial nerve lesion

E- Complete R facial nerve lesion

F- R midpons lesion (main sensory nucleus)

G- R medullary lesion (spinal tract CN V)

H- Demyelinating peripheral polyneuropathy (all potentials may be markedly delayed or absent)

Question 3

This blink reflex depicts what?

Answer 3

demyelinating polyneuropathy

Pt with Guillain Barre syndrome and moderately severe bifacial weakness (L>R).

R1 prolonged at 21ms and ipsilateral R2 at 43ms.

Contralateral R2 barely present/prolonged at 46ms.

Question 4

This blink reflex depicts what?

Answer 4

Normal

R1 normally bi or triphasic and stable from stim to stim.

R2 is variable and polyphasic.

Here the R1 is at 11ms and R2 at 34ms.