Cranial Nerve XI, The Spinal Accessory Nerve
This nerve is tested by first observing the patient for atrophy or fasciculation in the trapezius muscles, shoulder drooping or displacement of the scapula. The patient is then instructed to turn head and shrug shoulders against resistance. Weakness in turning head in one direction indicates problem in contralateral CN XI, while weakness in shoulder shrug indicates ipsilateral CN XI lesion .