12 days of Cranial Nerves: Accessory nerve
Accessory nerve is the 11th cranial nerve, having a purely motor function. Its function is innervating the sternocleidomastoid and trapezius muscles. Sternocleidomastoid muscle allows head rotation, while trapezius - to shrug shoulders.
Accessory nerve is divided into its spinal and cranial components. Spinal component arises from the upper part of the spinal cord, entering the cranium via foramen magnum. It travels to reach the jugular foramen, briefly encountering the cranial component before exiting the skull. Then, it runs along the internal carotid artery, eventually reaching the sternocleidomastoid muscle, which it innervates. It then moves across to supply motor fibres to the trapezius. Its cranial component arises from the medulla oblongata, leaving the cranium via the jugular foramen, and then combining at the inferior ganglion of the vagus nerve.
What if it isn’t working properly?
Then a person might experience accessory nerve palsy, characterised by muscle wasting and partial paralysis of the sternocleidomastoid, resulting in the inability to rotate the head or weakness in shrugging the shoulders. Damage to muscles may lead to asymmetrical neckline
What conditions might affect the accessory nerve?
Causes of accessory nerve damage are mostly iatrogenic, or being a result of injury during a medical procedure. Procedures such as cervical lymph node excision biopsy or central line insertion can cause trauma to the nerve.
