Past Papers · SAQ
Cranial Nerve Reflexes
2021B Q18
Exam questionOutline the neural pathways for the pupillary light, corneal, oculomotor and gag reflexes. The anatomical course of nerves is NOT required.
CICMWrecks answer
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
Past papers
Exam appearances
| Exam | Exact exam wording | Candidate success |
|---|---|---|
| 2021B Q18 | Outline the neural pathways for the pupillary light, corneal, oculomotor and gag reflexes. The anatomical course of nerves is NOT required. | 43% |