The accessory nerve is also known as cranial nerve 11. It arises from the brainstem, the medulla to be precise, below the glossopharyngeal and vagus nerve. It emerges lateral to the olive (an ovaloid structure responsible for pathways of motor learning and hearing).
The nerve has a spinal division and a cranial division, with the division occurring close to its origin. The cranial division runs with the vagus nerve (and leaves via the jugular foramen) and is distributed with the superior laryngeal and pharyngeal branches of the vagus nerve. The nerve leaves the skull through the jugular foramen, along with cranial nerves 9 (Glossopharyngeal) and 10 (Vagus). It also innervates the palatoglossus, which is a muscle that initiates swallowing; it also prevents saliva spillage into the oropharynx (this is achieved by maintaining the palatoglossal arch). It is innervated by this nerve, and is the only tongue muscle that is not innervated by the 12th nerve.
The spinal accessory nerve arises from the fibers of the ventral horn cells between C1 and C5 of the cervical plexus. The nerve then ascends through the foramen magnum and leaves through the jugular foramen. It leaves the skull via the jugular foramen and innervates the sternocleidomastoid (rotates the head), and the trapezius (shrugs the shoulder). It passes in the same sheath of the vagus nerve, which it is separated from it by a fold of arachnoid. As the nerve exits the jugular foramen, it passes posterolaterally and runs behind the digastric and stylohyoid muscles, to reach the superior portion of the sternocleidomastoid. As the nerve passes behind the muscle, it unites with the C2 spinal nerve. It unites with the C3 spinal nerve in the posterior triangle of the neck, and unites with the C4 spinal nerve deep to trapezius and forms a plexus of nerves. After the nerve has pierced the muscle, it runs across the posterior triangle of the neck, and terminates on the deep surface of the trapezius muscle.
11th nerve palsy- The accessory nerve is vulnerable to damage due to its relatively superficial course in the cervical region. Injuries to the nerve result in weakness of the trapezius and sternocleidomastoid muscles. Trapezius denervation causes drooping of the shoulder, winged scapula and weakness of shoulder flexion. Sternocleidomastoid denervation results in weakness of neck rotation, and a asymmetrical neckline. Damage occurs following lymph node biopsy, carotid vessel surgery or facelift procedures.
Myelencephalon (secondary brain vesicle)
Spinal division Sternocleidomastoid, Trapezius
Cranial division- Palatoglossus, muscles of the pharynx
When the anatomy professor asks the student what the accessory nerve does, he shakes his head and shrugs his shoulders. The professor says ‘correct!’
These are the actions of the sternocleidomastoid and trapezius muscles, both innervated by the accessory nerve.
The accessory nerve has a spinal and cranial division. The spinal division innervates the sternocleidomastoid and trapezius, and the cranial division joins the vagus nerve and pharyngeal plexus, supplying the muscles of the region.
1. Frank H.Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders, Chapter 1 Head and Neck
2. Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier
3. Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier
4. Elliiot L.Manchell: Gray's Clinical Neuroanatomy: The Anatomic Basis for Clinical Neuroscience
5. The Definitive Neurological Surgery Board Review
By Shawn P. Moore, 2005
6. Human Neuroanatomy
By James R. Augustine, 2008