Professional and Linguistic Assessments Board (PLAB) Practice Exam

Which of the following describes the function of the trochlear nerve (CN IV)?

1. Movement of the lateral rectus muscle

2. Movement of the superior oblique muscle

3. Facial sensation

4. Head and neck movement

The correct answer is: Movement of the superior oblique muscle

The trochlear nerve, also known as cranial nerve IV, is responsible for innervating the superior oblique muscle of the eye. This muscle plays a critical role in eye movement, particularly in actions involving downward and lateral gaze. When the trochlear nerve functions properly, it allows for smooth coordination of eye movements, which is essential for activities such as reading and tracking moving objects. The other options provided do not accurately reflect the function of the trochlear nerve. For example, the lateral rectus muscle is controlled by the abducens nerve (CN VI), while facial sensation is primarily conducted by the trigeminal nerve (CN V). Head and neck movements are mainly governed by other cranial nerves, particularly the accessory nerve (CN XI) and branches of the vagus nerve (CN X). Understanding the specific functions of cranial nerves is important for diagnosing and managing neurological issues that may arise in patients.