The accessory nerve arises from cranial and spinal roots; however, the cranial aspect joins the vagus nerve and is believed to actually be a part of the vagus nerve. Thus CN XI is often referred to as the spinal accessory nerve.
CN XI motor function is clinically tested by assessing the ability of the patient to turn his/her head and shrug his/her shoulders against opposing pressure.
CN XI innervates the sternocleidomastoid muscle which tilts and rotates the head.
CN XI innervates the trapezius muscle which is responsible for shoulder elevation.
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