The accessory nerve of Willis, also known as the cranial nerve XI or the spinal accessory nerve, is one of the twelve pairs of cranial nerves that originate from the brain. It is classified as a motor nerve and primarily serves the function of controlling certain muscles involved in the movement of the head and shoulders.
The accessory nerve of Willis is composed of two parts: the cranial part and the spinal part. The cranial part arises from the medulla oblongata, which is the lowermost part of the brainstem, while the spinal part originates from nerve roots in the upper part of the spinal cord.
The cranial portion of the accessory nerve primarily innervates and controls certain muscles of the throat, including the sternocleidomastoid and the trapezius muscles. These muscles are responsible for various movements of the head and neck, such as rotating the head, tilting it to the side, and shrugging the shoulders.
The spinal part of the accessory nerve primarily innervates the trapezius muscle, which is a large muscle located on the upper back and shoulders. It plays a crucial role in the movement and stabilization of the shoulder blades.
Damage or dysfunction of the accessory nerve of Willis can lead to various symptoms, such as weakness or paralysis of the muscles it innervates. This can result in difficulties in performing movements of the head, neck, and shoulders, as well as muscle atrophy or wasting. Rehabilitation and physical therapy may be recommended to improve muscle strength and function in individuals with accessory nerve disorders.
