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 (CN X), plays a crucial role in the autonomic nervous system, which is responsible for regulating involuntary functions within the human body. This nerve carries both sensory and motor fibe ...

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 part of the reticular formation named by Jacob Clarke. The nucleus ambiguus contains the cell bodies of neurons that innerva ...

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 (CN X), plays a crucial role in the autonomic nervous system, which is responsible for regulating involuntary functions within the human body. This nerve carries both sensory and motor fiber ...

. 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 ...

, where it may interchange fibers with the spinal portion 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 inferio ...

of the vagus. It then passes through the

jugular The jugular veins () are veins that take 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 muscle. Struc ...

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 Musculus may refer to: *Andreas Musculus (1514–1581), German Lutheran theologian *Heinrich Musculus (b. 1868), Swedish-Norwegian businessperson *Wolfgang Musculus (1497–1563), German Reformed theologian *Musculus (bivalve), ''Musculus'' (bivalv ...

and

Levator veli palatini The levator veli palatini () is a muscle of the soft palate and pharynx. It is innervated by the vagus nerve (cranial nerve X) via its pharyngeal plexus. During swallowing, it contracts, elevating the soft palate to help prevent food from enteri ...

. 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