Aery involved in 3rd cranial nerve lesion?
**Core Concept**
The 3rd cranial nerve, also known as the oculomotor nerve, controls several extraocular muscles, including the medial rectus, superior rectus, inferior rectus, and inferior oblique. A lesion in this nerve can lead to impaired eye movements and pupillary constriction.
**Why the Correct Answer is Right**
The oculomotor nerve originates from the midbrain and exits through the superior orbital fissure. It is involved in the innervation of the superior rectus, medial rectus, inferior rectus, and inferior oblique muscles, which are responsible for eye movements. A lesion in the 3rd cranial nerve can lead to ptosis, diplopia, and impaired pupillary constriction due to the involvement of the parasympathetic fibers that control the sphincter pupillae muscle.
**Why Each Wrong Option is Incorrect**
* **Option A:** The abducens nerve (6th cranial nerve) is involved in the innervation of the lateral rectus muscle, which is responsible for outward eye movement. A lesion in this nerve would lead to impaired abduction, not the symptoms associated with a 3rd cranial nerve lesion.
* **Option B:** The trochlear nerve (4th cranial nerve) is involved in the innervation of the superior oblique muscle, which is responsible for downward and inward eye movement. A lesion in this nerve would lead to impaired downward gaze, not the symptoms associated with a 3rd cranial nerve lesion.
* **Option C:** The trigeminal nerve (5th cranial nerve) is involved in the sensory innervation of the face and motor innervation of the muscles of mastication. A lesion in this nerve would lead to impaired facial sensation or mastication, not the symptoms associated with a 3rd cranial nerve lesion.
**Clinical Pearl / High-Yield Fact**
A 3rd cranial nerve lesion can be caused by an aneurysm of the posterior communicating artery, which is a common cause of isolated oculomotor nerve palsy.
**Correct Answer:** C.