All are motor nerves except - - RUHS, Jaipur, PB B.Sc Nursing Entrance-2024

RUHS, Jaipur, PB B.Sc Nursing Entrance-2024

Applied Physiology

Easy

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2024

Explanation

The Optic nerve, also known as Cranial Nerve II (CN II), is a purely sensory nerve.
Its sole function is to transmit visual information from the retina of the eye to the brain.
Unlike motor nerves, it does not control any muscle movement, making it the correct exception in the given options.

Option A: The Oculomotor nerve (CN III) is a primary motor nerve responsible for controlling most of the eye's movements, including four of the six extraocular muscles, the muscle that raises the eyelid (levator palpebrae superioris), and the muscles responsible for pupil constriction.
Option C: The Trochlear nerve (CN IV) is a motor nerve. It is unique as it innervates only one muscle: the superior oblique muscle of the eye, which is essential for downward and inward eye rotation.
Option D: The Hypoglossal nerve (CN XII) is a motor nerve that provides motor control to all the intrinsic and most of the extrinsic muscles of the tongue. Its function is critical for articulation (speech) and swallowing.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of Cranial Nerves by Function as background academic context rather than a clinical decision trigger.
Assessing cranial nerve function is a fundamental part of a neurological examination. A nurse must be able to differentiate between sensory and motor nerve functions to accurately identify and report specific neurological deficits.
Damage to the Optic nerve results in various forms of vision loss, whereas damage to the Oculomotor, Trochlear, or Hypoglossal nerves causes motor deficits like double vision (diplopia), drooping eyelid (ptosis), or difficulty with speech (dysarthria) and swallowing (dysphagia).
What if? If a patient presents with a drooping eyelid (ptosis) and a dilated, non-reactive pupil, the nurse should suspect a lesion of the Oculomotor nerve (CN III), not the Optic nerve, as these are signs of motor and parasympathetic dysfunction.

How to Approach the Question

First, identify the keyword 'except'. This signals that you must find the option that is different from the others.
The question establishes the category as 'motor nerves'. Your task is to find the nerve that is NOT a motor nerve.
Recall the functional classification of the 12 cranial nerves: Sensory, Motor, or Mixed (Both). A helpful mnemonic is 'Some Say Marry Money But My Brother Says Big Brains Matter More'.
Systematically evaluate each option against this classification:
Oculomotor (CN III) -> 'Marry' -> Motor
Optic (CN II) -> 'Say' -> Sensory

Concept Tested & Keywords

Concept Tested: Classification of Cranial Nerves by Function
Stem keywords: motor nerves, cranial nerves
Lead-in keywords: except
Negative lead-in flag: The question asks for the option that does not fit the described category (motor nerve).

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