Cranial nerve · one in each half of the brain
Accessory nerve (XI)
Also called Cranial nerve XI, CN XI, Spinal accessory nerve, Eleventh nerve
Lets you shrug your shoulders and turn your head, and takes a strange U-turn to get there.
The accessory nerve powers two big muscles: the strap-like muscle on the side of your neck that turns your head, and the trapezius, the large muscle that shrugs your shoulders. Its path is odd. Its fibers start in the top of the spinal cord, climb up into the skull, and then leave the skull again on their way to the neck.
Where it is
Its fibers start in the upper spinal cord in the neck, rise through the big opening at the base of the skull, then exit beside the vagus nerve and run down to the neck and upper back.
What it does
Turning the head
It powers the sternocleidomastoid, the strap-like muscle on the side of the neck. The left one turns your head to the right, and the right one turns it to the left.
Shrugging
It powers the trapezius, which lifts your shoulders and helps you raise your arm above your head.
Steady posture
It helps hold your head steady and keeps your shoulders from sagging.
Think of it as the puppet string for your neck and shoulders: one tug turns your head, another lifts your shoulders in a shrug.
Works with
- Spinal cordMost of its fibers start from nerve cells in the top part of the spinal cord.
- Medulla oblongataIt runs up alongside the medulla before leaving the skull.
- Vagus nerve (X)It leaves the skull right beside the vagus, and a small part of it joins the vagus.
- Primary motor cortexThe motor cortex sends the commands to shrug and turn your head.
- Motor neuronIts fibers are the long cables of motor neurons that make the neck and shoulder muscles contract.
When it goes wrong
How doctors check it
"Shrug your shoulders against my hands" and "turn your head against my hand". The doctor feels for weakness on one side.
Nerve injury
In the side of the neck the nerve runs close to the skin, so it can be hurt during neck surgery or an injury. The shoulder then droops, and lifting the arm overhead becomes hard and often painful.
For learning only, not medical advice. If you have a health concern, talk to a doctor.
Surprising facts
- Unusually for a cranial nerve, it enters the skull from below and then leaves it again.
- Every time you shake your head "no", the two sides of this nerve help by taking turns pulling your head left and right.
By the numbers
Where the name comes from
From the Latin accessorius, "extra" or "helper". A small part of it joins the vagus nerve, which it travels beside for a short stretch.
Quick quiz
3 questions. Your answers are saved and come back in your daily review.
Which of these is a job of the accessory nerve (XI)?
Show the answer
Turning the head. It powers the sternocleidomastoid, the strap-like muscle on the side of the neck. The left one turns your head to the right, and the right one turns it to the left.
Turning the head. It powers the sternocleidomastoid, the strap-like muscle on the side of the neck. The left one turns your head to the right, and the right one turns it to the left.
The accessory nerve (XI) is part of which larger structure?
Show the answer
Cranial nerves. It belongs to the cranial nerves.
Cranial nerves. It belongs to the cranial nerves.
Which part fits this description? "Like the puppet string for your neck and shoulders: one tug turns your head, another lifts your shoulders in a shrug."
Show the answer
Accessory nerve (XI). It is the accessory nerve (XI). Lets you shrug your shoulders and turn your head, and takes a strange U-turn to get there.
Accessory nerve (XI). It is the accessory nerve (XI). Lets you shrug your shoulders and turn your head, and takes a strange U-turn to get there.
These parts now come back in your daily review, just before you would forget them.
Practice it and its neighbors in 3DSources
- Neuroanatomy, Cranial Nerve 11 (Accessory), StatPearls, NCBI Bookshelf
- Accessory Nerve Injury, StatPearls, NCBI Bookshelf
- Accessory nerve, Radiopaedia
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