CN XI: Accessory nerve

CN XI: Accessory nerveAnatomy and function of the accessory nerve
~ 5 min

In this note, we are going to discuss the anatomy and function of the accessory nerve (n. accessorius), or the 11th cranial nerve (CN XI).

Accessory nerve (nervus accessorius)
Accessory nerve (nervus accessorius)

It innervates the sternocleidomastoid and trapezius muscles.

Sternocleidomastoid muscle (m. sternocleidomastoideus)
Sternocleidomastoid muscle (m. sternocleidomastoideus)
Trapezius muscle (m. trapezius)
Trapezius muscle (m. trapezius)

According to the generally accepted classification of functional components, it contains general somatic efferent fibers (GSE) and special visceral efferent fibers (SVE). That means that it is a motor nerve.

Some authors recognize only one of the listed types of fibers in the accessory nerve (either GSE or SVE). This is due to the fact that the sternocleidomastoid and trapezius muscles are not directly derived from the pharyngeal arches. In classical anatomy, the nerve was described only as a general (or somatic) sensory efferent nerve (GSE). However, according to modern data, certain parts of these muscles are still derived from the pharyngeal arches. In this regard, we cannot exclude the presence of SVE fibers.

The fibers of the accessory nerve arise from the two nuclei and form two divisions.

The cranial division arises from the nucleus ambiguus (nucleus ambiguus), which is located in the dorsal part of the medulla oblongata.

Nucleus ambiguus (nucleus ambiguus)
Nucleus ambiguus (nucleus ambiguus)
Nucleus ambiguus (nucleus ambiguus)
Nucleus ambiguus (nucleus ambiguus)

The axons of these neurons exit the brain along the posterior border of the olive and form the cranial root of the accessory nerve (radix cranialis).

Сranial root of the accessory nerve (radix cranialis)
Сranial root of the accessory nerve (radix cranialis)

The spinal division arises from the spinal accessory nucleus (nucleus spinalis nervi accessorii), which is located in the cervical spinal cord, specifically in the posterolateral aspect of the anterior horn.

Spinal accessory nucleus (nucleus spinalis)
Spinal accessory nucleus (nucleus spinalis)

The axons of these neurons form the spinal root of the accessory nerve (radix spinalis).

Spinal root of the accessory nerve (radix spinalis)
Spinal root of the accessory nerve (radix spinalis)

It ascends inside the vertebral canal (canalis vertebralis) as the spinal accessory nerve,

Vertebral canal (canalis vertebralis)
Vertebral canal (canalis vertebralis)

enters the cranial cavity through the foramen magnum (foramen magnum) and merges with the cranial root to form the common trunk of the accessory nerve.

Foramen magnum (foramen magnum)
Foramen magnum (foramen magnum)

The accessory nerve exits the cranial cavity through the jugular foramen (foramen jugulare).

Jugular foramen (foramen jugulare)
Jugular foramen (foramen jugulare)
Location of the spinal root in the posterior cranial fossa
Location of the spinal root in the posterior cranial fossa

Then it splits into two branches: the internal branch (r. internus), and the external branch (r. externus).

Internal branch (ramus internus)
Internal branch (ramus internus)
Internal branch (ramus externus)
Internal branch (ramus externus)

The internal branch is formed by the fibers of the cranial root and continues its course along the pharyngeal and laryngeal branches of the vagus nerve.

Internal branch (ramus internus)
Internal branch (ramus internus)

Some authors still consider only its spinal division to be the accessory nerve and attribute the cranial division directly to the vagus nerve.

Nervus vagus (nervus vagus)
Nervus vagus (nervus vagus)

The external branch consists of the fibers originating from the spinal root.

External branch (r. externus)
External branch (r. externus)

It travels inferiorly, along the internal carotid artery and runs deep to the sternocleidomastoid muscle, providing motor innervation to it.

Sternocleidomastoid muscle (m. sternocleidomastoideus)
Sternocleidomastoid muscle (m. sternocleidomastoideus)
Accessory nerve on the internal surface
of the sternocleidomastoid muscle
Accessory nerve on the internal surface<br />
of the sternocleidomastoid muscle

Reaching the anterior border of the trapezius muscle, the nerve divides into its terminal branches.

Trapezius muscle (m. trapezius)
Trapezius muscle (m. trapezius)
Dictionary

CN XI: Accessory nerve

Accessory nerve
n. accessorius
Nucleus ambiguus
nucleus ambiguus
Cranial root
radix cranialis
Spinal nucleus
nucleus spinalis
Spinal root
radix spinalis
Vertebral canal
canalis vertebralis
Foramen magnum
foramen magnum
Jugular foramen
foramen jugulare
Internal branch
ramus internus
External branch
ramus externus
Vagus nerve
nervus vagus
Sternocleidomastoideus muscle
m. sternocleidomastoideus
Trapezius muscle
m. trapezius
Main screen of the Easy Anatomy app

Download Easy Anatomy and try it for free

  • Anatomical atlas
  • Interactive notes
  • Videos on Anatomy
  • Flashcard tests

Easy Anatomy

Learn anatomy effectively

3.2K

Функция доступна в приложении

Download the app