Cranial nerve XI

Cranial Nerve XI

The cranial nerve XI, also known as the accessory nerve.

The Cranial Nerve XI, also known as the Accessory Nerve, is a nerve in the human anatomy that controls the sternocleidomastoid and trapezius muscles, which are responsible for movements of the head and the shoulders. It is unique among the cranial nerves as it is the only one that originates from both the brain and the spinal cord.

Structure

The accessory nerve is composed of two parts: the cranial part, which arises from the medulla, and the spinal part, which arises from the upper segments of the spinal cord. The two parts join to form the accessory nerve, which then splits again to innervate the sternocleidomastoid and trapezius muscles.

The cranial and spinal parts of the accessory nerve.

Function

The accessory nerve provides motor innervation to the sternocleidomastoid and trapezius muscles. The sternocleidomastoid muscle is involved in turning the head to the opposite side, while the trapezius muscle is involved in shrugging the shoulders and moving the scapula.

Clinical significance

Damage to the accessory nerve can result in weakness or paralysis of the sternocleidomastoid and trapezius muscles. This can cause difficulties in turning the head or shrugging the shoulders. It can also result in a condition known as winged scapula, where the scapula protrudes from the back in an abnormal position.

A winged scapula, a possible result of accessory nerve damage.

See also

• Cranial nerves
• Sternocleidomastoid muscle
• Trapezius muscle
• Winged scapula