All of the following are mixed cranial nerves, EXCEPT:

DSSSB October 2024

Applied Anatomy

Easy

Appeared in: DSSSB October 2024

Explanation

The Abducens nerve (CN VI) is the correct answer because it is a purely motor nerve, not a mixed nerve.
Its sole function is to provide motor innervation to the lateral rectus muscle of the eye.
This muscle is responsible for abduction of the eye, which means moving the eye outward, away from the nose.
Since the question asks for the exception among mixed nerves, the purely motor Abducens nerve is the correct choice.

Option A: The Trigeminal nerve (CN V) is a mixed nerve. It has a large sensory component for the face, scalp, and oral cavity, and a motor component that controls the muscles of mastication (chewing).
Option B: The Facial nerve (CN VII) is a complex mixed nerve. It controls the muscles of facial expression (motor), carries taste sensation from the anterior two-thirds of the tongue (sensory), and provides parasympathetic innervation to the lacrimal and salivary glands (motor).
Option D: The Vagus nerve (CN X) is a mixed nerve with the most extensive distribution. It provides sensory and motor (parasympathetic) innervation to the pharynx, larynx, and organs in the thoracic and abdominal cavities.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Functional classification of cranial nerves as background academic context rather than a clinical decision trigger.
Assessing cranial nerve function is a fundamental part of a neurological examination. A nurse tests the Abducens nerve (CN VI) by asking the patient to follow their finger as it moves laterally (to the side).
Damage to the Abducens nerve, known as CN VI palsy, results in the inability to abduct the affected eye. This causes the eye to turn inward (esotropia) and leads to horizontal double vision (diplopia), which worsens when the patient looks toward the affected side.
What if? If a patient presented with a drooping face and inability to smile on one side, the nurse would suspect a lesion of the Facial nerve (CN VII), not the Abducens nerve, as CN VII controls the muscles of facial expression.

How to Approach the Question

First, recognize the negative framing of the question due to the word 'EXCEPT'. This means you are looking for the option that does not belong to the specified group.
The group specified is 'mixed cranial nerves'. Recall that mixed nerves have both sensory and motor functions.
Systematically evaluate each option to determine its functional classification (sensory, motor, or mixed).
Trigeminal (V) is mixed. Facial (VII) is mixed. Vagus (X) is mixed.
Abducens (VI) is purely motor.
The option that is the exception is the Abducens nerve.

Concept Tested & Keywords

Concept Tested: Functional classification of cranial nerves
Stem keywords: mixed cranial nerves, Trigeminal nerve, Facial nerve, Abducens nerve, Vagus nerve
Lead-in keywords: EXCEPT
Negative lead-in flag: The question asks for the option that is an exception.

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