Where are the cranial nerves?
They leave the underside of the brain and brainstem and pass through openings in the skull. They are numbered I to XII from front to back.
What do the cranial nerves do?
Smell (I), vision (II), eye movements (III, IV, VI), facial sensation and chewing (V), facial expression and taste (VII), hearing and balance (VIII), swallowing and the gag reflex (IX, X), shoulder shrug and head turning (XI) and tongue movement (XII).
Clinical relevance of the cranial nerves
- A dilated pupil that no longer reacts (pressure on CN III) is a late sign of increased intracranial pressure and brain herniation.
- Bell's palsy affects CN VII: one whole side of the face droops, including the forehead. A stroke usually spares the forehead.
- Trigeminal neuralgia (CN V) causes brief, severe stabbing facial pain triggered by touch, chewing or cold air.
Nursing focus: the cranial nerves
- Check the gag reflex and swallowing (CN IX and X) before giving anything by mouth after a stroke or sedation.
- In Bell's palsy, protect the eye on the affected side with artificial tears and an eye patch or taping at night.