page_title: Accessory nerve
section_title: Function
hierarchical_section_title: Accessory nerve / Function
caption_attribution_description: Illustration from Anatomy &amp; Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013.
context_page_description: The accessory nerve is a cranial nerve that supplies the sternocleidomastoid and trapezius muscles. It is considered as the eleventh of twelve pairs of cranial nerves, or simply cranial nerve XI, as part of it was formerly believed to originate in the brain. The sternocleidomastoid muscle tilts and rotates the head, while the trapezius muscle, connecting to the scapula, acts to shrug the shoulder.
  Traditional descriptions of the accessory nerve divide it into a spinal part and a cranial part. The cranial component rapidly joins the vagus nerve, and there is ongoing debate about whether the cranial part should be considered part of the accessory nerve proper. Consequently, the term "accessory nerve" usually refers only to nerve supplying the sternocleidomastoid and trapezius muscles, also called the spinal accessory nerve.
  Strength testing of these muscles can be measured during a neurological examination to assess function of the spinal accessory nerve. Poor strength or limited movement are suggestive of damage, which can result from a variety of causes. Injury to the spinal accessory nerve is most commonly caused by medical procedures that involve the head and neck.
context_section_description: The spinal component of the accessory nerve provides motor control of the sternocleidomastoid and trapezius muscles. The trapezius muscle controls the action of shrugging the shoulders, and the sternocleidomastoid the action of turning the head. Like most muscles, control of the trapezius muscle arises from the opposite side of the brain.  Contraction of the upper part of the trapezius muscle elevates the scapula. The nerve fibres sternocleidomastoid however are thought to change sides (Latin: decussate) twice. This means that the sternocleidomastoid is controlled by the brain on the same side of the body. Contraction of the stenocleidomastoid fibres turns the head to the opposite side, the net effect meaning that the head is turned to the side of the brain receiving visual information from that area. The cranial component of the accessory nerve, on the other hand, provides motor control to the muscles of the soft palate, larynx and pharynx.
caption: The accessory nerve supplies the sternocleidomastoid and trapezius muscles
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