Accessory nerve

A cranial nerve that plays a vital role in neck and shoulder movement.

The accessory nerve, also known as cranial nerve XI, is a unique cranial nerve primarily responsible for controlling the muscles in the neck and shoulder. It emerges from the upper spinal cord and brainstem, branching out to innervate specific muscles involved in head movement and shoulder elevation.

Terminologia Anatomica

nervus accessorii

System

Nervous system

Function

The accessory nerve facilitates crucial movements in the body through its motor functions. It primarily innervates the sternocleidomastoid and trapezius muscles. The sternocleidomastoid muscle is critical for rotating the head and flexing the neck, enabling the action of looking over one’s shoulder. Additionally, the trapezius muscle is essential for shrugging the shoulders and stabilizing the upper limb during arm movements. By contributing to these movements, the accessory nerve aids in performing everyday activities, from simple tasks like turning one's head to more complex actions such as lifting and carrying objects. The overall functionality provided by this nerve also supports good posture and movement coordination, showcasing its importance in overall body mechanics.

Location

The accessory nerve has a unique anatomical route as it arises from two distinct sources; the spinal part originates from the upper cervical spinal cord (C1 to C5) and the cranial part emerges from the medulla oblongata of the brainstem. After its formation, it travels upward through the jugular foramen, a bony opening located at the base of the skull. Once it exits the skull, the accessory nerve branches into the sternocleidomastoid and trapezius muscles, traversing the neck and lateral aspect of the upper thorax to reach its target muscles. This intricate pathway highlights the importance of the accessory nerve in ensuring efficient communication between the brain and the muscles it controls.

Did You Know?

The accessory nerve is unique because it has components that originate from both the brain and the spinal cord, distinguishing it from other cranial nerves.
In a common clinical evaluation, the function of the accessory nerve is tested by asking an individual to shrug their shoulders against resistance.
Damage to the accessory nerve can lead to difficulty in shoulder elevation and neck rotation, commonly affecting a person's daily activities.
Some anatomical diagrams distinguish the 'accessory nerve' and 'spinal accessory nerve,' reflecting its dual origins.