Have you ever wondered what makes us able to move our head from side to side? Or how we can shrug our shoulders with ease? It might not be something that would normally cross our mind since all these movements come so naturally to us. Our body is full of nerves. These send signals from our brain to the different organs and muscles in our body.
Whenever we touch something that causes pain or pleasure, these nerves send a message to the brain that informs us of what kind of feeling it is. The brain then sends a signal back to the area, telling the nerves how to react. For example, if it’s hot, the brain will tell the nerves to remove the area as fast as possible.
What Is the Spinal Accessory Nerve?
The SAN is the 11th of 12 sets of cranial nerves. It was initially thought to be of the cranial nerve group, but now researchers aren’t so sure. It was discovered that the spinal accessory nerve loses its cranial rootlets to the vagus nerve, which is located right above it.
The spinal accessory nerve is traditionally divided into cranial and spinal parts.
The cranial portion is significantly smaller than the spinal part and starts from the lateral side of the medulla oblongata. It departs the brain through the large jugular foramen. Here it will very shortly touch the other portion of the nerve; the spinal part.
The cranial part of the nerve will then join the vagus nerve, after leaving the skull. The cranial portion will then give the fibers to the vagus nerve which then takes over.
The spinal part starts from the nerve cells of the irreplaceable upper spinal cord. The C1-C5 and C6. These fibers come together to create the spinal portion of the nerve. This bundle of fibers enters the intracranial space through the foramen magnum. It then reaches the jugular foramen. This is where the two parts meet.
After briefly meeting with the cranial part, it exits the skull.
After exiting the skull, the nerve makes its way down next to the outstanding internal carotid artery to the sternocleidomastoid muscles. Next, it quickly moves on to the huge trapezius muscles.
Functions of the Spinal Accessory Nerve
The SAN is connected to two muscles:
- Trapezius muscle
The Sternocleidomastoid Muscle
You can find the sternocleidomastoid muscles on each side of the neck. These muscles allow us to move our heads. Each one is long and thick and starts at the thorax, ending at the base of the skull, right underneath the ear. If the sternocleidomastoid gets strained or damaged it can become quite painful. Sudden movements, such as whiplash, often cause severe damage to this muscle.
Symptoms of an injury include:
- Piercing pain if the head is tilted.
- Muscular fatigue.
- Difficulty holding the head upright
In severe cases you might notice:
- Reddening and swelling around the area.
- Muscle spasms
Using a warm or cold compress is an excellent way to treat a strain. If the pain or symptoms are severe, you can perform simple stretching and strength exercises to treat the area. If the pain persists, this could be an indication that there might be a more serious problem.
The Trapezius Muscles
The trapezius muscles are a pair of extensive muscles that cover the majority of our upper back. They control the movement of the shoulders and arms.
If these muscles are injured, this can cause severe damage to the SAN, One of these injuries is called trapezius muscle palsy. It is caused by a sudden movement or jerking of the arm and shoulder, or trauma to the neck. The symptoms can be excruciating and hard to deal with if left untreated.
- Muscle weakness.
- Reduced movement of the shoulder and arm.
- Pain in the trapezius muscle.
- Visible trapezius wasting.
Physiotherapy is the first step in treating this injury. If it doesn’t help and the pain is still present, surgery might be the only option.
Where Is the Spinal Accessory Nerve Located?
The spinal accessory nerve controls two immense muscles that manage our neck and shoulder functions. But where exactly is the nerve?
The spinal accessory nerve is a combination of four to five rootlets that exit from the center of the brain stem, and five to six rootlets that exit from the cervical vertebrae, which is located immediately below the neck. These rootlets join together into one strong fiber which runs up the side of the brain stem and into the skull.
Spinal Accessory Nerve Injuries
Injuries can occur, and this nerve is actually very vulnerable due to its location.
Due to its function, any injury can result in loss of movement in the upper body. Injuries will also cause a significant amount of pain.
How Does an Injury Occur?
An injury to the spinal accessory nerve can happen during any surgical procedure in the neck area. Cervical lymph node removal and radical neck dissection are the procedures that most often cause the injury. Furthermore, it is commonly seen in cancer patients. Since this nerve is very vulnerable, any trauma or damage caused by surgery can leave it injured.
Moreover, an injury can occur due to a faulty placed IV needle. Doing a repetitive motion using the two muscles (the sternocleidomastoid and trapezius) has been known to injure the nerve. This is due to the strain and pressure placed on the nerve. But in these cases, it will heal on its own, as long as the spinal accessory nerve isn’t broken.
Spinal Accessory Nerve Palsy
Spinal accessory nerve palsy (SAN palsy) is similar to trapezius muscle palsy, but not quite the same. Trapezius muscle palsy is paralysis of the muscle. SAN palsy is paralysis of the nerve. This will affect not only the trapezius muscle, but also the sternocleidomastoid muscle causing pain to neck, shoulders and arm.
A significant difference between the two conditions is that trapezius muscle palsy can be treated, whereas it is difficult to treat SAN palsy without surgical interference.
The symptoms of SAN palsy are very similar to those of trapezius muscle palsy. It can be challenging to move the neck and shoulders and will cause a considerable amount of pain.
- “Hanging” shoulder: the affected shoulder appears to be lower than the healthy one.
- Difficulty lifting; even light items become difficult or impossible to lift.
- Altered shoulder mechanics.
- Pain and weakness in the shoulder.
To find out if a patient is suffering from SAN palsy, a physician will examine the patient’s medical and physical history. Once this is done, the doctor will move on to make a physical examination of the injured area.
As we saw in the symptoms, the injured shoulder will be visibly lower than the other, and is key physical evidence the examiner will look for. A physician will also assess motor function in the sternocleidomastoid and trapezius muscles. The patient could be asked to perform different movements, such as: shrugging the shoulders, moving the arms or tilting and rotating the head. These movements will help the doctor make a diagnosis.
Another way SAN palsy is sometimes diagnosed is during surgery that caused the damage in the first place.
SAN palsy can be treated through physiotherapy. It consists of several different exercises that should restore the nerve’s functions. These exercises include:
- Stretching exercises.
- Strengthening exercises.
If physical therapy isn’t successful and the patient is still experiencing pain, the next step would be a surgical procedure.
There are different surgeries that can repair SAN palsy such as:
- Nerve surgery.
- Nerve grafting.
- Nerve regeneration.
For patients not responding to nerve surgery, there is another way out; a muscle transfer, which will help stabilize the scapula. Another round of physical therapy will be administered for the patient after the surgery, to rehabilitate the nerve as it is imperative to rebuild the strength of both the muscle and the nerve.
In other cases, a brace can be fitted for the patient. The brace will help to improve the posture of the patient; therefore, lifting some of the pressure off the nerve to help it heal.
Any Long-Term Effects?
As long as the nerve has healed, whether it is through physiotherapy or surgery, there shouldn’t be any long-term effects. But if the physiotherapy or surgery was not successful, the patient might still be experiencing symptoms of SAN palsy.
The spinal accessory nerve is an amazing powerhouse. It controls two of the major, and essential muscles in our upper body, the sternocleidomastoid and the trapezius. Without it, it would be incredibly difficult for us to perform daily tasks. Even just raising an arm over the head wouldn’t be possible.
Injuries can occur, and the nerve is vulnerable because it is located close to the skin in the back of the neck. Damage is usually caused by surgical procedures in the neck area. These can be treated with physiotherapy or nerve surgery. It can cause long-term effects, such as pain and lowered motor skills in the neck, shoulder and arm.