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The Spinal Accessory Nerve (SAN) or Cranial Nerve 11 is termed a cranial nerve as it was originally believed to originate in the brain. It has both a cranial and a spinal part, though debate still rages regarding whether the cranial part is a part of the SAN or part of the vagus nerve. [1] The cranial part, along with the cranial nerves 9 and 10, supplies innervation to the soft palate, larynx and pharynx. The spinal part supplies innervation to the Sternocleidomastoid and Trapezius muscles.[2]
Root
The spinal part on the SAN arises from C1- C5/6 nerve roots.
The smaller cranial part originates from the lateral aspect of the medulla oblongata.
Cranial Portion: travels from the medulla up to the jugular foramen to exit and join the vagus nerve on its way to supply the soft palate, larynx and pharynx.
Spinal Portion: Travels upwards as the C1-C5/6 spinal root section joins together and exits out the jugular foramen, with the cranial portion. It goes on to supply the Sternocleidomastoid and Trapezius muscles.[2]
Function
Motor innervation
Contributes to the supplying of the soft palate, larynx and pharynx muscles ( with larger contributions from cranial nerves 9 and 10 )
Sternocleidomastoid muscles
Trapezius muscle
Sensory - surrounded by controversy
As the Trapezius and sternocleidomastoid muscles are derived from the pharyngeal arches some believe they must carry special visceral efferent information and others argue that they must contain general somatic efferent information.[1]
Clinical relevance
Injury to the SAN causes varying degrees of dysfunction in the Trapezius muscle and the Sternocleidomastoid muscle.
The various causes of injury include
neck trauma
wrenching injury to arm or neck
surgical procedures such as lymph node biopsy, parotid surgery, carotid surgery and jugular vein cannulation.[4]
Radiation therapy to the lymph nodes in the neck
Aneurysms of the internal carotid artery
Fracture of the atlas bone or hyoid due to direct trauma
The following conditions may affect nerve function eg Pharyngo-cervical-brachial variant of Guillain-Barre-syndrome, Sandifer syndrome, Eagle-syndrome, Diphtheria (infection), Poliomyelitis or Tetanus (both situations that rarely can affect the XI nerve), botulism, and sarcoidosis. Other causes are diabetes, vitamin B12 deficiency, and tumours.[5]
Assessment
A thorough medical and objective history should be carried out to determine the reasons for damage and the extent of the damage.
Traditional physiotherapeutic methods are the mainstay of treatment. This is directed at restoring function to the shoulder girdle with emphasis on the sternocleidomastoid and trapezius muscle. Methods employed may include:
Taping eg McConnell taping to facilitate trapezius action
Use of acute brief low-frequency electrostimulation eg TENS, has been found in some studies to be beneficial in axonal growth[8]
Sling use several hours a day to help with pain management
Cervical PNF patterns extension to flexion with rotation and Scapular PNF patterns from anterior depression to posterior elevation[9]
If physiotherapy is not successful other options are then considered including
Nerve surgery, nerve grafting, nerve regeneration
Tendon of muscle transfers to stabilise scapular eg scapulothoracic fusion[4], Modified Eden Lange Procedure[11]
Surgical options comprise nerve surgery, nerve grafting, and nerve regeneration. Other treatment options include tendon or muscle transfer to stabilise the scapula, employed for patients not responding to nerve repair or surgery. One of the widely used surgical procedures is scapulothoracic fusion.
Additional viewing
To learn more about the ways that nerves heal after injury watch the great 8 minutes video clip below
↑ 5.05.1Bordoni B, Varacallo M. Neuroanatomy, Cranial Nerve 11 (Accessory) [Updated 2018 Oct 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507722/ (last accessed 22.3.2019)
↑Dr. Ray Pulmano DC. Cranial Nerve XI: Motor Testing of the Trapezius and Sternocleidomastoid. Available from: http://www.youtube.com/watch?v=M0DY8yUUaO8[last accessed 25/5/2024]
Sternocleidomastoid muscles
Trapezius muscle