Accessory nerve

The accessory nerve (XI) is a motor cranial nerve that originates from both the medulla oblongata and the cervical spinal cord and supplies muscles of the neck and shoulder region.

Number : XI

Sensory, motor, or both : motor

Origin : the cranial roots arise from the caudal part of the nucleus ambiguus in the medulla oblongata, while the spinal roots arise from the motor nucleus of the accessory nerve in the lateral part of the ventral gray column of the first to seventh cervical spinal cord segments.

Route / Reports : the spinal roots ascend cranially between the dorsal and ventral roots of the cervical spinal nerves and enter the cranial cavity through the foramen magnum. They join the cranial roots on the ventrolateral surface of the medulla to form the accessory nerve. The nerve then divides into internal and external branches. The external branch leaves the cranial cavity through the jugular foramen and tympanooccipital fissure together with the vagus and glossopharyngeal nerves, then courses caudally in the neck.

Distribution : the internal branch joins the vagus nerve, while the external branch supplies the trapezius, cleidocephalicus, and sternocephalicus muscles through dorsal and ventral branches.

Description : The accessory nerve originates from cranial roots in the medulla oblongata and spinal roots in the cervical spinal cord. The spinal roots enter the skull through the foramen magnum and join the cranial roots to form the nerve. Its internal branch joins the vagus nerve, whereas its external branch exits through the jugular foramen and tympanooccipital fissure and continues into the neck to innervate the trapezius, cleidocephalicus, and sternocephalicus muscles.