Bell palsy is a facial nerve disorder
Bell palsy is a sudden, usually one-sided weakness or paralysis of the face caused by inflammation of the facial nerve (cranial nerve VII). The cause is presumed to be viral, with swelling of the nerve inside its narrow bony canal in the temporal bone. The facial nerve supplies the muscles of facial expression, so damage produces drooping of the mouth, flattening of the nasolabial fold, inability to smile or puff the cheek, and inability to close the eyelid on the affected side.
Why the forehead matters
Involvement of the forehead tells the nurse that the problem is in the facial nerve itself, not in the brain. The upper face receives nerve input from both sides of the brain, while the lower face receives input mainly from the opposite side. A stroke above the facial nucleus therefore weakens the lower face but spares the forehead. In Bell palsy, the peripheral nerve is affected after these inputs have joined, so the whole side of the face, including the forehead, is weak. This client cannot raise his right eyebrow or close his right eye, which fits a peripheral lesion of cranial nerve VII.
| Cranial nerve | Main function | Typical disorder |
|---|
| III Oculomotor | Raises upper eyelid, moves the eye, constricts pupil | Ptosis, dilated pupil |
| V Trigeminal | Facial sensation, chewing muscles | Trigeminal neuralgia |
| VII Facial | Facial expression, eyelid closure, taste on front of tongue | Bell palsy |
| VIII Vestibulocochlear | Hearing and balance | Hearing loss, vertigo |
Why the other nerves do not fit
The oculomotor nerve raises the upper eyelid; damage causes a drooping eyelid (ptosis) that cannot open, which is the opposite of an eye that cannot close. The trigeminal nerve carries facial sensation and moves the jaw; its classic disorder is trigeminal neuralgia, with brief, severe stabbing pain rather than weakness. The vestibulocochlear nerve serves hearing and balance and has no role in facial movement.
Nursing relevance
Because the eyelid cannot close, the cornea is at risk of drying and abrasion. Nursing care therefore centers on eye protection: artificial tears during the day, lubricating ointment, and taping the eyelid closed at night. Other care includes soft foods chewed on the unaffected side, oral care to remove food trapped in the cheek, facial exercises, and reassurance, since most clients recover over weeks to months.
Exam takeaway
Key point Sudden one-sided facial droop with the forehead involved and inability to close the eye points to Bell palsy and cranial nerve VII. Facial pain without weakness points to cranial nerve V.