What Is the Accessory Nerve?

Nerves carry signals from the brain to organs and muscles in the body. The accessory nerve (SAN) is a spinal nerve. It is the 11th of 12 pairs of cranial nerves. The nerve divides into cranial and spinal divisions and it’s coiled in appearance.

What Does the Accessory Nerve do?

The accessory nerve is a motor nerve that supplies the trapezius and sternocleidomastoid muscles. The nerve is responsible for motor function and is necessary for the muscles to work.

Diagram Accessory nerve


The trapezius connects to the scapula and is responsible for shoulder movement. The muscle consists of upper, middle and lower fibers. The upper fibers lift the shoulder and the middle and lower fibers rotate and lower it.

The trapezius is an important muscle that also helps to support and stabilize the scapula. A well supported scapula is essential for normal arm and shoulder movement.


The sternocleidomastoid is the muscle that rotates the head. This muscle controls left and right movement after receiving a signal from the brain via the accessory nerve. The sternocleidomastoid also enables the head to tilt back and forth.

Where is the Accessory Nerve?

Accessory nerve parts

The accessory nerve leaves the brain and passes through a large aperture at the base of the skull. The nerve passes down the neck close to the jugular vein, alongside the 9th and 10th cranial nerves. The accessory nerve then enters the sternocleidomastoid where it supplies the muscle.

The accessory nerve then continues to the trapezius muscle and innervates the upper part. The accessory nerve is the only cranial nerve that enters and exits the human skull. The nerve is close to the skin’s surface, making it susceptible to injury.

Accessory Nerve Injury

Surgery around the neck and head area is always dangerous due to the number of nerves, veins and arteries in the area. Because the accessory nerve is not very deep under the skin it’s at risk of injury. Any kind of injury to the accessory nerve will affect the way it functions, resulting in mobility impairment.

The symptoms of an accessory nerve injury include:


  • Numbness in the neck and shoulder
  • Limited neck and shoulder movement
  • Muscle weakness
  • Protruding shoulder blade


There are several ways the accessory nerve can be damaged during surgery; it could be severed or punctured. When the nerve gets injured during an operation it will affect the muscles that control the head and shoulder.

The accessory nerve can also become bruised during a surgical procedure on the neck. Although bruising will cause some damage, this is not as serious as a severed or punctured nerve. The bruising will heal over a period of time without medical treatment.

Lymph Node Excision

If a surgeon needs to carry out lymph node excision during an operation, the accessory nerve is at risk of injury. A surgeon will have to open up the neck with a small incision to remove one or more lymph nodes. During the procedure, the accessory nerve can be subject to blunt or penetrating trauma.

IV Damage

The accessory nerve can be injured if an IV (intravenous) needle is inserted into the neck for any reason. If the accessory nerve gets punctured, the penetrating trauma will cause some damage. As long as the nerve is not severed or impaired, it should recover without treatment.

Repetitive Motion Injury

Repetitive motion injury can cause damage to the accessory nerve in some cases. Everyday tasks such as washing a vehicle, working in the garden or cleaning the house can cause an injury. Repeating the same movement over and over can put unnecessary strain and pressure on the accessory nerve.


Exposure to high doses of radiation therapy can also damage the accessory nerve. Patients with head or neck cancer are often required to undergo a course of radiotherapy. As well as targeting the cancer cells, the radiation attacks healthy nerves which can lead to complications.

Shoulder Dislocation

Shoulder Dislocation xray
of all joints dislocations

Shoulder dislocation is a common injury that accounts for 50% of all joint dislocations. When the shoulder leaves the socket, it can damage the accessory nerve in some cases. When the joint and muscle move from their natural place, the nerve can become stretched.

Whiplash Injury

Whiplash injuries sustained in car accidents are very common and this can also damage the accessory nerve. The forces put on the neck are high which results in the nerve injury. Although accessory nerve damage from whiplash is rare, there is medical evidence to say it can occur.

SAN Palsy

Damage to the accessory nerve can also cause a condition known as spinal accessory nerve palsy. SAN palsy can lead to paralysis of the neck and shoulder muscles. The shoulder will droop as a result. Muscle wastage is likely to take place, due to lack of use. Patients also experience some pain and discomfort.

Patients diagnosed with SAN palsy do not have any standard treatment options. The symptoms can be managed, and physiotherapy will strengthen muscles in the shoulder and neck. A brace may also be put in place to stabilize the scapula. This approach will provide some pain relief.

In more serious cases, patients may need surgery to manage the pain and discomfort associated with SAN palsy. Nerve reconstruction may be an option and in some patients the scapula will be attached to a rib. The surgery is not likely to cure the condition, but it does help to make the symptoms more tolerable.

Winged Scapula

Another condition associated with accessory nerve injury is a winged scapula. The condition results in the shoulder blade sticking out. This is painful, uncomfortable and debilitating. The condition also weakens neck and shoulder muscles and the arm can also be affected.

Winged scapula can be treated in various ways. In many patients, physiotherapy is the first option. A doctor may also describe painkillers, muscle relaxants or anti-inflammatory drugs to manage the pain. Shoulder braces are also used to reduce the pain associated with winged scapula.

If nonsurgical methods do not provide any relief, there is a surgical option known as a scapulothoracic fusion. This operation involves fusing the scapula to the ribs. However, this is a last resort, used only when other treatment has failed. Following this type of surgery, patients may be unable to lift their arm. Additionally, lung problems are also a complication associated with the surgery.


Torticollis is a condition also known as wry neck and it can develop when the accessory nerve is injured. Patients with torticollis have difficulty moving their head and the neck is in an abnormal position. The condition is painful, but the symptoms will usually subside without medical treatment after a few days.

If the symptoms associated with torticollis do not subside, some treatment options are available. Physiotherapy is an effective way to treat the condition, due to neck stretches and exercises. Surgery can also be carried out to dissect the 2 heads of the sternocleidomastoid muscle.

Is Accessory Nerve Damage Permanent?

When the accessory nerve has been damaged it can repair itself, although this will take some time. When the nerve has been subject to trauma but not cut, it should heal within in two or three months. If the nerve has been severed, it will begin to grow again, although it is not likely to heal completely without treatment.

An accessory nerve that has repaired itself will never completely recover and some symptoms may not subside. Neck and shoulder movement may still be limited, and muscle weakness is likely.

Can Accessory Nerve Damage be Repaired?

There are a few ways that a surgeon can repair a damaged accessory nerve to restore mobility in the neck and shoulder. Direct nerve repair can be carried out, where the two ends of the nerve are joined with stitches. This procedure is an effective way to repair an injured accessory nerve.

When the accessory nerve cannot be rejoined due to severe damage, a surgeon may decide that a nerve graft is the solution. The surgeon will take a length of nerve from the hand or foot and use it to join the two ends of the accessory nerve. This type of grafting helps to strengthen the injured nerve while it regrows.

It is worth noting that when a motor nerve is injured and does not heal itself, an operation to repair it should take place within 18 months. After this time, the injured nerve will begin to die, and a repair will no longer be possible. The muscle that supplied by the nerve will then become weak.

Final Thoughts

Now you have everything you need to know about the accessory nerve. You know why it’s there, what it does, where it is in the body and the reason it is so important. You also have some information on accessory nerve injuries and repair options.


Pin It on Pinterest

Share This