Which nerve and muscle are not functioning appropriately if a patient can move the eye medially but not down while looking toward their nose?

The correct answer is that the trochlear nerve and superior oblique muscle are not functioning appropriately in this scenario. The superior oblique muscle is primarily responsible for rotating the eye downward and outward (depression and intorsion). When a patient can move their eye medially but is unable to move it down while looking toward their nose, this suggests that the muscular control needed for inferior movement is compromised.

The trochlear nerve innervates the superior oblique muscle, and if this nerve is not functioning properly, it can lead to an inability to effectively move the eye downward in certain positions. In this case, while the patient can adduct the eye (move it medially) due to other muscles being intact, the specific action of depression is impaired because of the deficit related to the superior oblique muscle's function, which is crucial for moving the eye downward.

Understanding the roles of eye muscles and their corresponding nerves helps clarify this situation. The other options involve different muscles or nerves that are not relevant to the described symptoms, thus reinforcing why the trochlear nerve and superior oblique are the primary focus here.