Spinal accessory nerve

Spinal Accessory Nerve

The spinal accessory nerve.

The Spinal Accessory Nerve (SAN), also known as the eleventh cranial nerve or CN XI, is a cranial nerve that originates from the medulla oblongata and the spinal cord. It is primarily responsible for the motor innervation of the sternocleidomastoid muscle and the trapezius muscle, which control movements of the head and shoulders.

Structure

The spinal accessory nerve is unique among the cranial nerves as it has both a cranial and a spinal root. The cranial root arises from the medulla oblongata and joins the vagus nerve. The spinal root arises from the upper segments of the spinal cord and ascends to the foramen magnum, where it joins the cranial root.

Function

The spinal accessory nerve provides motor innervation to the sternocleidomastoid and trapezius muscles. The sternocleidomastoid muscle is involved in rotating the head, while the trapezius muscle moves the scapula and supports the arm.

Clinical significance

Damage to the spinal accessory nerve can result in shoulder drop, due to paralysis of the trapezius muscle, and difficulty in turning the head, due to paralysis of the sternocleidomastoid muscle. This can occur as a result of surgical procedures in the neck, particularly lymph node biopsies.

See also

• Cranial nerves
• Nervous system
• Neuroanatomy