Blink reflex and facial nerve

1. What is the pathway taken during the blink reflex?
2. What pathology affects R1 vs. R2?
3. How is NCS of the facial nerve performed?
4. What is synkinesis?
5. How can the facial nerve CMAP be used to determine prognosis?

Answers:
1. The supraorbital branch of the trigeminal nerve is stimulated, which propagates into the pons and branches to the lateral medulla, then branches to innervate the bilateral orbicularis oculi via the facial nerve. The R1 response goes through the pons only, but the R2 response goes through the pons and lateral medulla.
2. R1 is affected by lesions of the trigeminal nerve, pons, and facial nerve. R2 is affected by consciousness level, Parkinson's disease, lateral medullary syndrome, Valium, and habituation.
3. Stimulation is distal to the stylomastoid foramen at the angle of the mandible and recorded over the nasalis muscle.
4. Synkinesis is the aberrant regeneration of axons in facial nerve injuries leading to reinnervation of inappropriate muscles.
5. Patient can be monitored over 2 weeks. Demyelinating has better outcome than axonal injury. If CMAP is <10%> poor outcome. 10-30% normal has a fair prognosis. Greater than 30% has a good prognosis and recovery is expected within 2 months.