The Accessory Nerve: Anatomy, Function, And Treatment

Describe the origin, course, distribution, and applied anatomy of the accessory nerve.

Answer:

The accessory nerve is the CN 11. Accessory Nerve is purely a motor nerve and consists of two roots – cranial and spinal.

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Accessory Nerve Origin and Course

The cranial root arises from the nucleus ambiguus in the medulla oblongata. It emerges on the surface of the medulla between the olive and inferior cerebellar peduncle.
The spinal root arises from the upper five cervical spinal segments.
The spinal root ascends to enter the cranial cavity through the foramen magnum. It then turns laterally to join the cranial root. The united roots leave the skull through the jugular foramen, but just outside the foramen, they separate again.

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Accessory Nerve Distribution

The spinal root descends in the neck to supply the sternocleidomastoid and trapezius muscles. The cranial root joins the vagus and is distributed through its branches. The distribution of the cranial root of the accessory nerve is as follows:

Accessory Nerve supplies all the muscles of the palate through the pharyngeal plexus except the tensor tympani, which is supplied by the mandibular nerve.
Accessory Nerve supplies all the muscles of the pharynx through the pharyngeal plexus except the stylopharyngeus, which is supplied by the glossopharyngeal nerve.
Accessory Nerve supplies all the intrinsic muscles of the larynx through superior and recurrent laryngeal nerves (branches of the vagus nerve).

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Accessory Nerve Applied anatomy

The lesion of the accessory nerve leads to paralysis of the sternocleidomastoid and trapezius. It is tested clinically:

By asking the patient to shrug his/her shoulder (trapezius) against the resistance.
By asking the patient to turn his/her face to the opposite side (sternocleidomastoid) against the resistance.