Focused anatomy reference
Accessory Nerve
Updated for this reference edition: 4 October 2026
The accessory nerve is the eleventh cranial nerve, usually written as CN XI. It is primarily a motor nerve: its fibres help control muscles used for head turning, shoulder elevation, swallowing, and voice production. Understanding its route is useful because the nerve has two traditionally described roots and its fibres are closely associated with the vagus nerve.
What is the accessory nerve?
Cranial nerves emerge from the brain or brainstem and carry information to or from structures in the head and neck. The accessory nerve is classified as a motor nerve. In traditional descriptions, it has a cranial root linked with the medulla and a spinal root linked with the upper cervical spinal cord.
The simple idea
Think of CN XI as a movement pathway for several muscles that position the head, lift the shoulder, and support coordinated actions in the throat and larynx.
Origin and course
The two roots differ in their starting points and paths. They travel together briefly, leave the skull through the jugular foramen, and then separate again in the neck.
Cranial root
The cranial root is traditionally described as arising from the nucleus ambiguus in the medulla. Its fibres join the vagus nerve after passing through the jugular foramen. Through vagal branches, they contribute to motor control of muscles in the pharynx, soft palate, and larynx.
Spinal root
The spinal root arises from motor neurons in the anterior grey matter of the upper cervical spinal cord. Rootlets ascend through the foramen magnum, join the cranial root for a short distance, and leave the skull through the jugular foramen. In the neck, the spinal portion supplies the sternocleidomastoid and trapezius muscles.
Functional components and nuclei
The accessory nerve is described as carrying motor fibres rather than sensory fibres. Its associated cell bodies are found in two principal areas:
Associated with the nucleus ambiguus in the medulla and functionally linked with vagal branches.
Located in the upper cervical spinal cord and connected with the sternocleidomastoid and trapezius.
Supports purposeful movement rather than carrying ordinary skin sensation.
Functions
The spinal component helps the sternocleidomastoid turn and flex the head. When the trapezius contracts, it helps elevate the shoulder and contributes to movement and stability of the shoulder blade.
Fibres associated with the cranial root travel with the vagus nerve to muscles involved in swallowing and voice production. Because these pathways work as a network, the accessory nerve is best understood alongside the vagus nerve and other lower cranial nerves.
Injury, symptoms, and testing
An injury affecting the accessory nerve can weaken the trapezius and sternocleidomastoid on the involved side. Possible signs include a lower shoulder position, difficulty elevating the arm above shoulder level, and reduced strength when turning the head against resistance. Voice or swallowing changes usually suggest involvement of related vagal pathways or more than one lower cranial nerve, rather than an isolated spinal portion alone.
How clinicians assess it
A clinician may ask a person to shrug both shoulders against resistance and compare the trapezius muscles. They may also ask the person to turn the head against resistance while observing and feeling the sternocleidomastoid. These simple observations are part of a wider neurological examination and do not identify the cause by themselves.
Important context
New weakness, difficulty swallowing, changes in speech, or persistent voice changes need appropriate medical assessment. This page is an educational reference, not individual medical advice.
Summary
The accessory nerve is cranial nerve XI and is mainly motor. Its traditionally described cranial and spinal roots follow different routes before and after the jugular foramen. The cranial component joins the vagus nerve, while the spinal component supplies the sternocleidomastoid and trapezius. Together, these pathways support head movement, shoulder elevation, swallowing, and voice-related muscle activity. Examination commonly includes resisted shoulder shrugging and head turning.