SPINAL ACCESSORY NERVE (CN XI)

 
 

The Origin and functional components

Spinal accessory nucleus. C1- C5

GSE


The Cours and distribution
  • Course dorsomedially

  • Take a 180° bend to exit the spinal cord laterally between the dorsal and ventral roots.

  • Ascend parallel to the spinal cord

  • Enter the cranial vault through foramen magnum
    .
  • Curves downward to exit the skull through the jugular foramen .


  • Descends in the neck in the company of the internal jugular vein.

  • Enters the medial surface of the sternomastoid muscle.

  • Joined by sensory fibres from upper cervical nerves


  • Traverses the posterior cervical triangle before entering the lower portion of the trapezius muscle.

 


Distribution

  • Innervates sternocleidomastoid and trapezius

 

Clinical Disorders of spinal accessory nerve

Damage to the nerve

...Can be caused by :

  • Poliomyelitis
  • Spinal injuries
  • Meningiomas
  • Neck wounds and tumors
  • Surgery in the posterior cervical triangle

....Results in:

  • Weakness in rotating the head down and away from the side of injury( sternomastoid muscle weakness)

  • Droop of the affected shoulder and an inability to shrug that shoulder

  • Reduced force when elevating the arm and shoulder against pressure

  • Inability to elevate shoulder above the horizontal plane.