Spinal accessory

Spinal Accessory Nerve

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

Anatomy

The Spinal Accessory Nerve is unique among the cranial nerves as it has both a cranial and a spinal root. The cranial root originates from the medulla oblongata, while the spinal root originates from the upper segments of the spinal cord. The two roots merge to form the Spinal Accessory Nerve, which then travels through the jugular foramen to reach the muscles it innervates.

Function

The primary function of the Spinal Accessory Nerve is motor innervation of the sternocleidomastoid and trapezius muscles. The sternocleidomastoid muscle is involved in rotating and flexing the head, while the trapezius muscle is involved in moving the shoulders and extending the neck.

Clinical Significance

Damage to the Spinal Accessory Nerve can result in a condition known as accessory nerve palsy. This can lead to weakness or paralysis of the sternocleidomastoid and trapezius muscles, resulting in difficulties with head rotation and shoulder movement. Common causes of accessory nerve palsy include surgical procedures in the neck region, trauma, and tumors.

See Also

• Cranial nerves
• Sternocleidomastoid muscle
• Trapezius muscle
• Accessory nerve palsy