What type of movement is primarily associated with the trochlear nerve (CN IV)?

The trochlear nerve, also known as cranial nerve IV, is specifically responsible for innervating the superior oblique muscle of the eye. This muscle is crucial for producing movements of the eyeball, particularly in enabling downward and inward (adduction) movement. When the superior oblique muscle contracts, it helps to rotate the eye downwards and towards the nose, making it essential for tasks that require precise visual tracking, especially when looking downwards at objects.

Understanding the function of the trochlear nerve is important in clinical practice. Damage to this nerve can result in difficulties with downward gaze, particularly when looking down stairs or reading, leading to symptoms such as diplopia (double vision). Thus, option A accurately reflects the primary movement associated with the trochlear nerve, confirming its role in directing the eye for specific functional movements.