Accessory nerve (CN) XI
The spinal accessory nerve innervates the sternomastoid and trapezius muscles. Its cranial component contributes to the pharyngeal plexus.
Place the palm of your hand against the right side of the subject’s jaw and ask him/her to turn the head to the right against this resistance while observing and feeling the left sternomastoid muscle (figure 41a-d).
Repeat the procedure for the right. The trapezius is tested by shoulder Shrugging (figure 42a,b).