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 The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spinal ...

as low as the fifth cervical nerve. Passing through the

lateral funiculus The most lateral of the bundles of the anterior nerve roots In anatomy and neurology, the ventral root of spinal nerve, anterior root, or motor root is the efferent motor root of a spinal nerve. At its distal end, the ventral root joins with the ...

of the medulla spinalis, they emerge on its surface and unite to form a single trunk, which ascends between the

ligamentum denticulatum Denticulate ligaments (also known as dentate ligaments) are lateral projections of the spinal pia mater forming triangular-shaped ligaments that anchor the spinal cord along its length to the dura mater on each side. There are usually 21 denticula ...

and the posterior roots of the spinal nerves; enters the skull through the foramen magnum, and is then directed 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 th ...

, through which it passes, lying in the same sheath of

dura mater In neuroanatomy, dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous syste ...

as 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 ...

, but separated from it by a fold of the

arachnoid Arachnoid may refer to: * Relating to arachnids * Arachnoid (astrogeology), a geological structure found only on the planet Venus * Arachnoid (botany), referring to organs with a cobwebby exterior appearance * Arachnoid granulation, small protr ...

. In the jugular foramen, it receives one or two filaments from the cranial part of the nerve, or else joins it for a short distance and then separates from it again. As it exits from the jugular foramen, it runs backward in front of the

internal jugular vein The internal jugular vein is a paired jugular vein that collects blood from the brain and the superficial parts of the face and neck. This vein runs in the carotid sheath with the common carotid artery and vagus nerve. It begins in the post ...

in 66.6% of cases, and behind it in 33% of cases. The nerve then descends obliquely behind the

Digastricus The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a small muscle located under the jaw. The term "digastric muscle" refers to this specific muscle. However, other muscles that have two separate muscle belli ...

and

Stylohyoideus The stylohyoid muscle is a slender muscle, lying anterior and superior of the posterior belly of the digastric muscle. It is one of the suprahyoid muscles. It shares this muscle's innervation by the facial nerve, and functions to draw the hyoid ...

to the upper part of the

Sternocleidomastoideus The sternocleidomastoid muscle is one of the largest and most superficial cervical muscles. The primary actions of the muscle are rotation of the head to the opposite side and flexion of the neck. The sternocleidomastoid is innervated by the acce ...

; it pierces this muscle, and courses obliquely across the posterior triangle of the neck, to end in the deep surface of the Trapezius. As it traverses the Sternocleidomastoideus it gives several filaments to the muscle, and joins with branches from the second cervical nerve. In the

posterior triangle Posterior may refer to: * Posterior (anatomy), the end of an organism opposite to its head ** Buttocks, as a euphemism * Posterior horn (disambiguation) * Posterior probability The posterior probability is a type of conditional probability that r ...

it unites with the second and third cervical nerves, while beneath the Trapezius it forms a plexus with the third and fourth cervical nerves, and from this plexus fibers are distributed to the muscle.

References

Accessory nerve {{Neuroanatomy-stub