Which cranial nerve is assessed by asking a patient to shrug their shoulders?

The correct answer is based on the function of cranial nerves that innervate certain muscles. The specific action of shrugging the shoulders primarily involves the trapezius muscle, which is innervated by the spinal accessory nerve, also known as cranial nerve XI. This nerve is responsible for controlling the sternocleidomastoid and trapezius muscles, which are crucial for shoulder elevation and head movement.

When a healthcare provider asks a patient to shrug their shoulders, they are specifically assessing the functioning of cranial nerve XI by observing the strength and symmetry of the shoulder elevation. If the nerve is functioning properly, the patient should be able to shrug their shoulders evenly and with adequate strength.

The other cranial nerves listed do not primarily involve the muscles responsible for shoulder movement. Cranial nerve IX (glossopharyngeal) is associated with swallowing and taste, cranial nerve X (vagus) is involved in autonomic functions and voice, and cranial nerve XII (hypoglossal) controls tongue movements. Therefore, the correct response directly correlates with the action being assessed.