Bell's palsy is caused due to involvement of which of the following nerve?

NIA - 29 January 2023

Applied Anatomy

Easy

Appeared in: NIA - 29 January 2023

Explanation

Bell's palsy is an idiopathic, acute peripheral paralysis of the Facial Nerve (Cranial Nerve VII).
The facial nerve controls the muscles of facial expression, making its dysfunction the direct cause of the unilateral facial weakness seen in this condition.
Symptoms include drooping of the mouth on one side, inability to close the eyelid, and loss of forehead wrinkles on the affected side.
It can also affect taste, tear production, and salivation because the facial nerve has sensory and parasympathetic functions.

Option A: The Trigeminal nerve (CN V) is primarily a sensory nerve for the face and controls the muscles of mastication (chewing). Its dysfunction leads to facial numbness or pain (trigeminal neuralgia), not facial muscle paralysis.
Option B: The Lingual nerve is a branch of the Trigeminal nerve (CN V) that provides general sensation to the anterior tongue. It does not control facial muscles.
Option D: The Abducens nerve (CN VI) is a motor nerve that controls a single extraocular muscle (the lateral rectus), responsible for moving the eye outward. Its paralysis causes inward deviation of the eye and double vision.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Etiology of Bell's Palsy and Cranial Nerve Function as background academic context rather than a clinical decision trigger.
The most critical nursing priority for a patient with Bell's palsy is protecting the affected eye from corneal injury due to the inability to blink or close the eyelid completely. This involves patient education on using artificial tears, ointments, and patching.
Nurses play a key role in assessing the patient's ability to eat and drink, as facial weakness can cause drooling and difficulty chewing, increasing the risk of poor nutrition and aspiration.
Psychosocial support is vital, as the sudden and dramatic change in facial appearance can cause significant emotional distress, anxiety, and social withdrawal.

How to Approach the Question

First, identify the key term in the question stem: 'Bell's palsy'.
Recall the definition and primary pathology of Bell's palsy. It is fundamentally a disorder of facial muscle control.
Consider the function of each cranial nerve listed in the options.
Match the function of the nerve to the symptoms of the condition. The Facial nerve (CN VII) is the primary nerve for muscles of facial expression.
Eliminate the other options by recalling their main functions: Trigeminal (facial sensation, chewing), Lingual (tongue sensation), and Abducens (eye movement).
Confirm that the Facial nerve is the only option responsible for the motor control of the face, which is affected in Bell's palsy.

Concept Tested & Keywords

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E6 Medicine Harrison 22e Part 2 pp. 1457-1459, 1459-1461, 1458-1460