Final answer:
To test the accessory nerve, patients are asked to perform movements and strength tests involving the sternocleidomastoid and trapezius muscles. This includes neck flexion, extension, lateral flexion, shoulder shrugging against resistance, and observing for any asymmetry or weakness which might indicate nerve damage.
Step-by-step explanation:
The function of the accessory nerve is tested by assessing the movement and strength of the head and neck, primarily via the sternocleidomastoid and trapezius muscles. To evaluate these muscles, the patient is asked to flex and extend the neck, shrug the shoulders against resistance, and perform lateral flexion of the neck toward the shoulder. Any noticeable asymmetry or weakness during these actions could indicate a compromised accessory nerve. The strength tests are part of the motor exam and are vital in checking the integrity of the spinal nerves that control skeletal muscles.
In addition, observing the elevation of the scapula and clavicle through the trapezius provides additional insight into the function of the accessory nerve as well as the cervical spinal nerves that contribute to these movements. Given that the spinal accessory nerve not only facilitates head and neck motion but also plays a role in movements of the trunk and shoulders, it is an important aspect of motor functionality.