RRB Nsg. Superintende…: Which cranial nerve is affected in a Bell's Palsy?

RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Applied Physiology

Easy

Appeared in: RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Explanation

Bell's Palsy is an idiopathic, acute paralysis affecting the facial nerve (Cranial Nerve VII).
This condition results in a lower motor neuron lesion, causing weakness or paralysis of all muscles on one side of the face, including the forehead.
Key signs include facial drooping, inability to close the eye, and disappearance of the nasolabial fold on the affected side.
It may also be associated with impaired taste, sensitivity to sound (hyperacusis), and pain around the ear.

Option A: Cranial nerve IX (Glossopharyngeal) is primarily involved in swallowing, the gag reflex, and taste sensation from the posterior third of the tongue. Its dysfunction does not cause facial paralysis.
Option B: Cranial nerve IV (Trochlear) is a motor nerve that controls a single eye muscle, the superior oblique. Damage to this nerve affects eye movement, specifically the ability to look down and inward.
Option D: Cranial nerve XII (Hypoglossal) is a motor nerve that controls the muscles of the tongue. Damage causes the tongue to deviate toward the side of the lesion upon protrusion.

Visual 1: Diagram - A clear illustration of the facial nerve (CN VII) pathway from the brainstem to the muscles of the face to show the extensive area it innervates.
Visual 2: Clinical Photo - A comparison of a person's face at rest and while attempting to smile, showing the classic signs of unilateral Bell's Palsy (e.g., drooping mouth, inability to close eye, smooth forehead).
Visual 3: Flowchart - A simple flowchart differentiating between an upper motor neuron (UMN) and lower motor neuron (LMN) facial palsy, highlighting that Bell's Palsy is an LMN lesion affecting the entire side of the face.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Identification of the cranial nerve affected in Bell's Palsy as background academic context rather than a clinical decision trigger.
A primary nursing responsibility for a patient with Bell's Palsy is protecting the affected eye. Since the patient cannot blink or close their eye completely, the cornea is at high risk for drying, ulceration, and injury. Meticulous eye care is crucial.
Nutritional assessment is important. Difficulty chewing and controlling food in the mouth can lead to poor intake, weight loss, and risk of aspiration. Nurses should provide dietary counseling and strategies for safe eating.
What if? If the patient's facial weakness only affected the lower part of their face (sparing the forehead), the nurse should suspect an upper motor neuron lesion, such as from a stroke, rather than Bell's Palsy. This is a critical distinction as it points to a central (brain) cause and requires immediate neurological workup.

How to Approach the Question

First, identify the key pathology mentioned in the question stem, which is "Bell's Palsy".
Second, access your knowledge of neurological disorders and the cranial nerves.
Recall the specific cranial nerve associated with Bell's Palsy. This is a direct recall question linking a condition to a specific anatomical structure.
Systematically review the options provided. Eliminate the nerves whose primary functions do not align with the signs of facial paralysis.
Confirm your answer by selecting the cranial nerve responsible for innervating the muscles of facial expression.

Concept Tested & Keywords

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Guyton & Hall Textbook of Medical Physiology 13e — Part 2 p. 711-712