Accessory nerve (spinal part)
This nerve is tested as follows.
1. Put your hands on the right and left shoulders of the patient and ask him to elevate (shrug) his shoulders. In paralysis the movement will be weak on one side (due to paralysis of the trapezius).
2. Ask the patient to turn his face to the opposite side (against resistance offered by your hand). In paralysis the movement is weak on the affected side (due to paralysis of the sternocleidomastoid muscle).