Canonical Question
Neuro – CN
Master answer
| Reflex | Examination technique | Normal response | Afferent pathway | Brainstem centers | Efferent pathway |
|---|---|---|---|---|---|
| Pupillary light | Response to light | Direct and consensual myosis followed by mydriasis | Retina, optic nerve, chiasma, optic tract | Pupillo-constrictor: midbrain, pretectal olivary nucleus, Edinger-Westphall nucleus Pupillo-dilator: posterior-lateral hypothalamus, cervical ganglion, trigeminal ganglion, abducens | Sympathetic fibers of CN III (Oculomotor) |
| Corneal | Stimulation of cornea with saline drops / cotton wisp | Eyelid closure | CN V (Trigeminal) | Pons, trigeminal and facial nuclei | CN VII (facial) |
| Occulomotor | Oculocephalic: Turn head from side to side | Eyes move conjugately in direction opposite to head | Semicircular canals, CN VIII (oculovestibular) | Pons (parapontine reticular formation), nucleus vestibularis, nucleus abducens | CN III (oculomotor) and VI (abducens) |
| Oculovestibular: Irrigate external auditory meatus with cold water | Nystagmus with fast component beating away with stimulus | ||||
| Gag / Pharyngeal reflex | Stimulation of solft palate | Symmetrical rise of soft palate gag reflex | CN IX (Glossopharyngeal) CN X (vagus) | Medulla, nucleus tractus solitarius | CN IX (Glossopharyngeal) CN X (vagus) |
Sources:
Benghanem, Sarah & Mazeraud, Aurélien & Azabou, Eric & Chhor, Vibol & Shinotsuka, Cássia & Claassen, Jan & Rohaut, Benjamin & Sharshar, Tarek. (2020). Brainstem dysfunction in critically ill patients. Critical Care. 24. 10.1186/s13054-019-2718-9.
Stevens, R., Sharshar, T., & Ely, E. (Eds.). (2013). Brain Disorders in Critical Illness: Mechanisms, Diagnosis, and Treatment. Cambridge: Cambridge University Press. doi:10.1017/CBO9781139248822
Exam appearances
| Exam | Exact wording | Relationship | Success |
|---|---|---|---|
| 2021B Q18 | Outline the neural pathways for the pupillary light, corneal, oculomotor and gag reflexes. The anatomical course of nerves is NOT required. | historical_member | — |