Which test is used to assess the function of cranial nerve XI?

The assessment of cranial nerve XI, also known as the accessory nerve, primarily focuses on its role in controlling certain muscles involved in head and shoulder movement. One key function of this nerve is to innervate the sternocleidomastoid muscle, which facilitates head rotation, and the trapezius muscle, which is responsible for shoulder shrugging.

When testing for cranial nerve XI, having the patient perform a shoulder shrug against resistance directly evaluates the function of the trapezius muscle. This action is critical in determining whether the muscle is receiving adequate nerve signals to perform its function effectively. If the shoulder shrug is weak or asymmetrical, it may indicate an issue with neural function related to the accessory nerve.

Therefore, assessing shoulder shrugs against resistance is a definitive test for cranial nerve XI, confirming its integrity and function. The other options involve different cranial nerves; head rotation against resistance primarily tests the sternocleidomastoid and can be somewhat ambiguous, while eye movement tracking assesses cranial nerves III, IV, and VI, and facial expression observation examines cranial nerve VII. These distinctions highlight why the shoulder shrug is the appropriate choice for assessing cranial nerve XI.