The cranial root of accessory nerve (or part) is the smaller of the two portions of the

accessory nerve The accessory nerve, also known as the eleventh cranial nerve, cranial nerve XI, or simply CN XI, is a cranial nerve that supplies the sternocleidomastoid and trapezius muscles. It is classified as the eleventh of twelve pairs of cranial nerv ...

. It is generally considered as a part of the vagus nerve and not part of the accessory nerve proper because the cranial component rapidly joins the

vagus nerve The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right ...

and serves the same function as other vagal nerve fibers. Recently, the concept of a cranial root of the accessory nerve has been challenged by new neuroanatomical studies which found that an unambiguous cranial root was not present in the majority of the cases. However, a small study in 2007 followed by a substantially larger study published in 2012Cranial roots of the accessory nerve exist in the majority of adult humans. Tubbs RS, Benninger B, Loukas M, Cohen-Gadol AA 2012 Clin Anat. doi: 10.1002/ca.22125 both confirmed that the cranial root of the accessory nerve is commonly found in humans, matching traditional descriptions.

Path

The cranial root fibers arise from the cells of the

nucleus ambiguus The nucleus ambiguus ("ambiguous nucleus" in English) is a group of large motor neurons, situated deep in the medullary reticular formation named by Jacob Clarke. The nucleus ambiguus contains the cell bodies of neurons that innervate the muscles ...

and emerge as four or five delicate rootlets from the side of the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

, below the roots of the

vagus The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right v ...

. It runs lateralward to the

jugular foramen A jugular foramen is one of the two (left and right) large foramina (openings) in the base of the skull, located behind the carotid canal. It is formed by the temporal bone and the occipital bone. It allows many structures to pass, including the i ...

, where it may interchange fibers with the

spinal portion The spinal root of accessory nerve (or part) is firm in texture, and its fibers arise from the motor cells in the lateral part of the anterior column of the gray substance of the medulla spinalis as low as the fifth cervical nerve. Passing through ...

or even become united to it for a short distance; here it is also connected by one or two filaments with the

jugular ganglion The superior ganglion of the vagus nerve, (jugular ganglion) is a sensory ganglion of the peripheral nervous system. It is located within the jugular foramen, where the vagus nerve exits the skull. It is smaller than and proximal to the inferior ...

of the vagus. It then passes through the

jugular The jugular veins are veins that take deoxygenated blood from the head back to the heart via the superior vena cava. The internal jugular vein descends next to the internal carotid artery and continues posteriorly to the sternocleidomastoid mus ...

foramen, separates from the spinal portion and is continued over the surface of the ganglion nodosum of the vagus, to the surface of which it is adherent, and is distributed principally to the pharyngeal and superior laryngeal branches of the vagus. Through the pharyngeal branch it probably supplies the

Musculus uvulæ The palatine uvula, usually referred to as simply the uvula, is a conic projection from the back edge of the middle of the soft palate, composed of connective tissue containing a number of racemose glands, and some muscular fibers. It also cont ...

and

Levator veli palatini The levator veli palatini () is the elevator muscle of the soft palate in the human body. It is supplied via the pharyngeal plexus. During swallowing, it contracts, elevating the soft palate to help prevent food from entering the nasopharynx. ...

. Some few filaments from it are continued into the trunk of the vagus below the ganglion, to be distributed with the recurrent nerve and probably also with the cardiac nerves.

Relationship to vagus

As the fibers from the presumptive cranial root may not join the accessory nerve at all or at best for a very short distance within the jugular foramen, it appears more useful to consider them in general to be part of the cranial roots of the vagal nerve. The accessory nerve would then be a pure motor nerve supplying the trapezius and sternocleidomastoid muscles, with the fibers originating from the spinal segments C1-C5 (the medullary root of the accessory nerve).

References

{{Authority control Accessory nerve