## **Core Concept**
The extraocular muscles are primarily controlled by the cranial nerves III (oculomotor), IV (trochlear), and VI (abducens). However, one of these muscles receives sympathetic innervation for its function.

## **Why the Correct Answer is Right**
The **superior tarsal muscle** (also known as Müller's muscle) is a small muscle in the eyelid that is involved in eyelid elevation. Unlike the main eyelid elevators (levator palpebrae superioris and superior tarsal muscle), it receives **sympathetic nervous system** innervation. This muscle is a smooth muscle and plays a role in the fine-tuning of eyelid elevation, particularly in maintaining the eyelid position.

## **Why Each Wrong Option is Incorrect**
- **Option A:** The **lateral rectus muscle** is innervated by the **abducens nerve (CN VI)**, which is a cranial nerve, not the sympathetic nervous system. It is responsible for outward gaze (abduction of the eye).
- **Option B:** The **medial rectus muscle** is innervated by the **oculomotor nerve (CN III)**, another cranial nerve. It is involved in inward gaze (adduction of the eye).
- **Option C:** The **levator palpebrae superioris** primarily elevates the eyelid and is innervated by the **oculomotor nerve (CN III)**, not the sympathetic nervous system.

## **Clinical Pearl / High-Yield Fact**
A key clinical correlation is **Horner's syndrome**, where disruption of sympathetic nerves to the eye results in ptosis (drooping eyelid), among other symptoms. This is because the sympathetic innervation to the superior tarsal muscle (Müller's muscle) is interrupted, affecting eyelid elevation.

## **Correct Answer:** D. Superior tarsal muscle.