By testing the movement of the lids, which of the cranial nerves are tested clinically?
**Core Concept**
The movement of the lids is primarily controlled by the musculature of the orbit, which is innervated by the third cranial nerve (oculomotor nerve) and the sympathetic nervous system. However, the primary cranial nerves responsible for testing lid movement clinically are the third cranial nerve and the seventh cranial nerve.
**Why the Correct Answer is Right**
The third cranial nerve (oculomotor nerve) controls the levator palpebrae superioris muscle, which elevates the upper eyelid. The seventh cranial nerve (facial nerve) controls the orbicularis oculi muscle, which closes the eyelid. Clinically, testing the movement of the lids involves assessing the function of these two nerves. A patient with a third cranial nerve palsy may have difficulty elevating their upper eyelid, while a patient with a seventh cranial nerve palsy may have difficulty closing their eyelid.
**Why Each Wrong Option is Incorrect**
**Option A:** The fifth cranial nerve (trigeminal nerve) primarily controls facial sensation and motor functions of mastication, and is not directly involved in lid movement.
**Option B:** The fourth cranial nerve (trochlear nerve) controls the superior oblique muscle, which is responsible for rotation of the eye, and is not directly involved in lid movement.
**Option C:** The sixth cranial nerve (abducens nerve) controls the lateral rectus muscle, which abducts the eye, and is not directly involved in lid movement.
**Clinical Pearl / High-Yield Fact**
When testing lid movement, it's essential to examine both the upper and lower eyelids, as a unilateral palsy of the third cranial nerve may result in a mild ptosis (drooping eyelid), while a unilateral palsy of the seventh cranial nerve may result in a mild weakness of eyelid closure.
**Correct Answer:** C.