Summary The Accessory Nerve (CN XI)

The Accessory Nerve (CN XI)


 The (spinal) accessory nerve only has a somatic motor function by innervating
the sternocleidomastoid and trapezius muscles

Anatomical course:

1. Spinal part –
 Originates from spinal nerve roots of the upper cervical spinal cord (primarily
C1-C6)
 Once joined, these nerve roots form the accessory nerve and run superiorly to
enter the cranial cavity through the foramen magnum
 It then transverses the posterior cranial fossa and exits the skull through the
jugular foramen with the glossopharyngeal and vagus nerves
 From here the spinal part descends following the course of the internal carotid
artery before reaching the sternocleidomastoid muscle which it innervates.
 After this point it continues across the posterior triangle of the neck to
innervate the trapezius muscle

2. Cranial part –
 Arises from the lateral aspect of the medulla oblongata in the brainstem
 It leaves the skull through the jugular foramen before combining with the
vagus nerve (CN X) at its inferior ganglion
 From here the fibres are distributed through the vagus nerve