Secondary action of Superior Rectus Muscle is ?
**Core Concept**
The superior rectus muscle is one of the six extraocular muscles responsible for controlling eye movements. Its primary action is elevation of the eyeball, but it also has a secondary action that contributes to its overall function.
**Why the Correct Answer is Right**
The secondary action of the superior rectus muscle is adduction (inward movement) of the eyeball. This is achieved through its oblique fibers, which insert onto the eyeball at an angle, allowing for this additional movement. The superior rectus muscle works in conjunction with the medial rectus muscle to produce smooth, coordinated eye movements. The oblique fibers of the superior rectus muscle are also responsible for its secondary action of extorsion (outward rotation) of the eyeball.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the inferior oblique muscle is responsible for extorsion (outward rotation) and elevation of the eyeball, not the superior rectus muscle.
**Option B:** This option is incorrect because the medial rectus muscle is primarily responsible for adduction (inward movement) of the eyeball, but it does not have a secondary action of elevation.
**Option C:** This option is incorrect because the inferior rectus muscle is responsible for depression (downward movement) of the eyeball, not the superior rectus muscle.
**Clinical Pearl / High-Yield Fact**
The superior rectus muscle's secondary action of adduction is essential for maintaining binocular vision and preventing diplopia (double vision) during eye movements.
**Correct Answer: C. Adduction**