Cranial Nerve X: Accessory Nerve
What’s unique about the Accessory Nerve?
The accessory nerve, also known as the spinal accessory nerve, is one of the most distinguishable and straight forward of the cranial nerves. Unlike other cranial nerves, its origin begins in the spinal cord below the foramen magnum. Its role is to provide motor function to two large muscles in the neck.
What is the function of the nerve?
Motor: Sternocleidomastoid (SCM) and Trapezius muscles
What are the signs of dysfunction?
Signs of vagus nerve dysfunction may include:
• Shoulder or neck pain
• Weakness of the shoulder
• Drooping of the shoulder
• Inability to shrug the shoulder
• Weakness turning the head to the side opposite the injury
How might this nerve be impacted?
The nerve may be impacted as a result of:
• Surgery, particularly to the cervical region
• Falls or accidents affecting the shoulder
• Compression or tumor in the jugular foramen
• Neurologic conditions such as motor neuron disease, poliomyelitis, syringomyelia, and brachial neuritis
How can you work with this nerve?
• Notice the spinal cord and foramen magnum. Also notice the temporal bones, occiput, and the jugular foramen. Offer space for decompression where it is needed.
• Visualize the pathway, from the spinal cord, moving through the foramen magnum alongside cranial nerves IX and X to exit through the jugular foramen, and moving down alongside the cervical spine to meet the SCM and the trapezius.
• Notice the quality of potency moving through the nerve.
• Hold space for any held patterns along the pathway to shift.
One of the most distinguishable cranial nerves, the accessory nerve arises from both the brainstem and the cervical spinal cord, located down in the cervical vertebrae.
The accessory nerve then ascends up through the foramen magnum.
It then traverses laterally through the posterior cranial fossa alongside cranial nerve ix, the glossopharyngeal nerve, and cranial nerve x, the vagus nerve.
It exits out the jugular foramen.
The accessory nerve then sends branches to two large muscles. First, the nerve innervates a large muscle in the front of our neck, the sternocleidomastoid muscle (SCM).
The SCM derives its name from its attachments; that is- the sternum and clavicle inferiorly, and the mastoid process of our temporal bone superiorly.
The SCM is responsible for cervical spinal flexion (tilting the head forward) as well as rotating the head and neck.
The accessory nerve also innervates a large muscle in our back, the trapezius muscle.
The trapezius muscle elevates the scapula, retracts the scapula, and depresses and rotates the scapula.