Final answer:
The trochlear nerve, also known as cranial nerve IV, is responsible for controlling the superior oblique muscle of the eye, allowing it to rotate downward and laterally.
Step-by-step explanation:
The trochlear nerve is the fourth cranial nerve, also known as CN IV. Its major function is the innervation of the superior oblique muscle, which is an extraocular muscle responsible for rotating the eye downward and laterally. This ability is crucial for proper eye movement and visual tracking, such as following objects within the visual field. The trochlear nerve is unique among the cranial nerves, as it innervates a muscle that allows for the downward and outward movement of the eyeball, an essential component of the complex coordination required for accurate vision.