Which nerve supplies superior oblique muscle of eye?

Appeared in: UP NHM CHO 7 Sept 2022 (Shift-2)

Explanation

The Trochlear nerve is the fourth cranial nerve (CN IV).
It is a motor nerve with the primary function of innervating a single extraocular muscle: the superior oblique.
The superior oblique muscle is responsible for moving the eye downward and inward (intorsion).
A common mnemonic to remember this is (LR6SO4)3, where 'SO4' stands for Superior Oblique supplied by the 4th cranial nerve.

Option B: The Oculomotor nerve (CN III) innervates four of the six extraocular muscles (superior rectus, inferior rectus, medial rectus, and inferior oblique), but it does not supply the superior oblique.
Option C: The Optic nerve (CN II) is a purely sensory nerve responsible for vision. It transmits visual signals from the retina to the brain and has no motor function.
Option D: The Trigeminal nerve (CN V) is a mixed nerve, but its motor functions are related to mastication (chewing), and its sensory functions relate to the face. It does not control eye movement.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Innervation of extraocular eye muscles as background academic context rather than a clinical decision trigger.
Damage to the trochlear nerve (CN IV palsy) can lead to paralysis of the superior oblique muscle.
This results in vertical diplopia (double vision), where one image appears above the other. The diplopia worsens when looking down and inwards (e.g., reading or walking downstairs).
Patients often compensate by tilting their head away from the affected side to minimize the double vision. This characteristic head tilt is a key diagnostic sign for nurses to observe.

How to Approach the Question

First, identify the key anatomical structures in the question: 'superior oblique muscle' and 'nerve'.
This is a factual recall question from anatomy that tests your knowledge of the cranial nerves and their specific functions.
Access your memory of the innervation of the extraocular muscles. A useful mnemonic is (LR6SO4)3.
Break down the mnemonic: LR6 = Lateral Rectus by CN VI (Abducens); SO4 = Superior Oblique by CN IV (Trochlear); 3 = All other muscles by CN III (Oculomotor).
Based on 'SO4', you can confidently select the Trochlear nerve as the correct answer.
Quickly review the other options to confirm they are incorrect. Oculomotor supplies other muscles, Optic is for vision, and Trigeminal is for facial sensation/chewing.

Concept Tested & Keywords

QAFCdYvn5Eg4sHPdRBW1A5

E6 Anatomy Applied Ashalatha 4e p. 426-428

E6 Physiology Ganong 27e Vol 2 Part 3 pp. 5-7, 4-6

Practise the full UP NHM CHO 7 Sept 2022 (Shift-2)

Attempt every question from this paper in a timed mock, then review the full solution for each one.