The Accessory Nerve Controls Shoulder and Neck Function (2025)

The accessory nerve provides motor function (movement) to two muscles essential to neck and shoulder movement, the sternocleidomastoid (SCM) and the trapezius, as well as to the larynx (voice box) and other structures in the throat. It’s the 11th of the 12 cranial nerves and is often referred to as CN XI.

While its official classification is as a cranial nerve, relaying information between the brain and parts of the body, it actually has two portions. One part originates in the brain and the other originates in the spine. For this reason, it’s often called the spinal accessory nerve.

Anatomy

All of the nerves in your body stem from either the brain or the spinal cord. They begin with what’s called a nerve root. Fibers from multiple nerve roots can combine to form a single nerve.

From their roots, they travel outward to the structures they supply nerve function to, which is called innervation. Most nerves send out multiple branches along the way, which innervate muscles, skin, and other tissues throughout the body.

Each nerve is actually a roughly symmetrical pair of nerves with one on each side of your spine. However, they’re typically referred to as a single nerve unless it becomes important to distinguish the left from the right (such as when discussing an injury).

Because of the complex origins of the accessory nerve, it’s generally discussed as two components:

• The spinal component
• The cranial component

Structure and Location

The spinal component of the accessory nerve is made up of roots from the sixth and seventh cervical vertebrae, which are in your neck. Once the nerve is formed, it runs up to enter the cranial cavity through an opening called the foramen magnum, which is a large opening near the back of the skull.

The nerve then travels through an area called the posterior cranial fossa in the back of your skull to reach a small opening off to the side called the jugular foramen.

The cranial component emerges in the brain from the medulla oblongata, which is the “stem” part of the brain stem that connects your brain to your spinal column. It then meets up with the spinal component and, together, they exit the skull through the jugular foramen.

They’re not together for long, though. Before they leave the jugular foramen, they split apart again.

The cranial component then joins the vagus nerve and follows it along its course in the throat. It’s often referred to as the internal branch of the accessory nerve. When it sends out branches, it does so via the vagus nerve, so it’s considered a part of that nerve, as well.

The accessory nerve sends fibers to the:

• Soft palate
• Larynx
• Pharynx

The spinal component, meanwhile, continues as the exterior branch. It moves downward along the internal carotid artery to pierce and innervate the SCM.

The SCM starts from behind your ear at the base of the skull, wraps around the side of your neck, and splits in two. One part of it connects to the sternum (breastbone), while the other attaches to the clavicle (collarbone).

The spinal component meets the SCM high in the back of the neck, then continues downward to innervate the trapezius muscle.

The trapezius is a large, triangular muscle. One point is at the base of the skull, another is far down the spine almost to the waist, and the third is near the shoulder joint.

Anatomical Variations

When studying anatomy, it’s important to remember that the way things are in most people isn’t the way they are in all people. Nerves, among other structures, often have known anatomical variations that doctors, and especially surgeons, need to know about in order to diagnose and treat people with nonstandard physiology.

The accessory nerve has numerous known anatomical variations, including:

• Several different possible relationships with the roots of the first cervical nerve
• Different positions regarding the internal jugular vein, sometimes traveling on one side or another, and sometimes even passing through it
• Different numbers of branches and different types of connection with the SCM muscle
• A possible relationship inside the skull with the facial nerve (CN VII), causing the involvement of CN VII in the innervation of the SCM
• Contributions to the spinal portion from the cervical plexus, a complex network of nerves in the neck, involving fibers from nerve roots of the second and third cervical vertebrae (C2 and C3)

Function

The accessory nerve is purely a motor nerve, which means it provides motion but not sensation.

Cranial Region

Via the vagus nerve, the cranial portion of the accessory nerve provides motion to some of the muscles in the soft palate, pharynx, and larynx. Those structures in the head and throat are involved in eating, speaking, and breathing.

The soft palate is just behind the roof of your mouth. It raises up to close off the airway and block the nasal passages when you swallow or suck. It also creates a vacuum in the oral cavity (your mouth) that keeps food out of your respiratory tract.

The pharynx is a cone-shaped cavity behind your nose and mouth. It connects your nasal and oral cavities to the esophagus, the tube that takes food from the mouth to the stomach. Its muscles contract to:

• Help push food into the esophagus
• Lift the walls of the pharynx when you swallow
• Keep you from swallowing air

The larynx, or voice box, holds your vocal cords. It’s a tube-like structure that attaches to the trachea (windpipe). When you breathe, air passes through the larynx before reaching the lungs.

While it’s best known for giving you a voice, the larynx also prevents food and other foreign objects from getting into your lower respiratory tracts.

Spinal Region

The spinal portion of the accessory nerve also innervates important muscles. Without a functional SCM and trapezius, the movement of your upper body would be severely limited.

The sternocleidomastoid muscle is essential for neck movement. Because it connects to two different points (sternum and clavicle), it can produce several different types of motion:

• When one part of the SCM contracts, it tilts your head to the same side. (For example, the muscle on the left side of your neck moves your head toward your left shoulder.)
• When the other part contracts, it turns your head to the opposite side (muscle on the left turns your head to the right) and turns your face up slightly.
• When both parts contract together, it can tilt your head backward toward your spine or lower your chin toward your sternum.
• When both the left and right SCM contract together (bilateral contraction), it thrusts your head forward.

The SCM also plays a role in breathing. When you breathe in, bilateral contraction lifts your breastbone and the area of the collarbones that’s closest to the center of your body.

The trapezius muscle performs many functions, most of which deal with moving the neck and shoulder. Its primary function is to stabilize and move the scapula (shoulder blade). However, it’s an extremely large muscle and the scapula requires multiple types of motion.

The type of movement depends on which portion of the muscle is involved:

• The upper portion of the muscle lifts and rotates the scapula and extends the neck.
• The middle portion of the trapezius pulls the scapula inward, closer to the body.
• The lower portion both lowers the scapula and assists the upper portion with upward rotation.

In addition, the trapezius:

• Helps you maintain an upright posture
• Is involved in turning and tilting the head
• Works with the deltoid muscle to allow you to throw an object

Associated Conditions

Due to its many important roles, a problem with the accessory nerve can impact numerous functions. The specific result depends on the location of the damage. The path of the nerve’s spinal (external) portion makes it especially prone to injury.

Some causes of accessory nerve dysfunction include:

• Diseases that cause irregularities in the foramen magnum and/or jugular foramen, which may result in compression of the nerve as it travels through those spaces
• Damage from blood loss due to aneurysms in nearby arteries
• Bone fracture that compresses the nerve
• Diseases that impair nerve function in general
• Lesions left behind from surgery in the region

Symptoms of damage to the accessory nerve include:

• Weakness, wasting, and loss of function in the muscles it innervates
• Partial paralysis of the muscle that results in restricted movement
• Neuropathy (nerve pain)
• Tension headache (due to spasm in the trapezius)

Rehabilitation

Treatment and management of problems with the accessory nerve are based on what’s causing the dysfunction.

For direct damage to the nerve itself, treatment may involve physical therapy (electrostimulation and strength exercises), an osteopathic approach to improve the movement of tissues impaired due to scarring, or nerve transfer.

Nerve Transfer

In a nerve transfer, one nerve or portion of a nerve is removed and put in place of the damaged nerve. Certain problems with the accessory nerve can be repaired this way. Conversely, portions of the accessory nerve are sometimes used to repair other nerves.

If the cranial portion of the accessory nerve is paralyzed, it can be replaced by portions of the axillary nerve in the brachial plexus, the network of nerves in the shoulder.

The accessory nerve is often used in nerve transfers to restore function to other areas when their nerves no longer function properly. It is commonly used to:

• Replace other nerves in the cervical plexus, including the radial, suprascapular, musculocutaneous, and axillary.
• Replace the phrenic nerve in people with quadriplegia (paralysis of all four limbs).