Spinal accessory nerve

Spinal accessory nerve refers to the spinal component of the accessory nerve, which innervates the sternocleidomastoid and trapezius muscles.

The accessory nerve is the eleventh cranial nerve, which is purely somatic motor. It comprises of spinal and cranial sub-components. The spinal sub-component (a.k.a. spinal accessory nerve) arises as nerve filaments from the C1-C6 cervical spinal motor nerve roots. These nerve filaments coalesce and ascend via foramen magnum to enter the cranial cavity. Here, the spinal accessory nerve combines with the cranial sub-component of the accessory nerve. The latter arises from caudal part of medulla oblongata (nucleus ambiguous). Together, they form the accessory nerve that exits the cranial cavity via the jugular foramen.

Outside the skull, the two sub-components, once again, separate to form cranial and spinal accessory nerves. The spinal sub-component innervates trapezius and sternocleidomastoid muscles. Whereas, the cranial sub-component adjoins the vagus nerve to form a pharyngeal plexus that innervates pharyngeal muscles.