The spinal accessory nerve (cranial part joining the spinal part) provides motor supply to the sternocleidomastoid and trapezius. The cell bodies giving rise to the spinal root of CN XI are located in which region?

• A Nucleus ambiguus of the medulla
• B Lateral grey column of the upper thoracic cord
• C Dorsal motor nucleus of the vagus
• D Anterior horn of the upper five cervical spinal segments ✓

Explanation

The spinal root arises from the spinal accessory nucleus, a column of motor neurons in the lateral part of the anterior grey horn extending from about D1 to D5. These fibers ascend through the foramen magnum, briefly join the cranial root from the nucleus ambiguus, then exit via the jugular foramen as a purely motor nerve. The nucleus ambiguus contributes to the cranial portion, which travels with the vagus.

Reference: Snell's Clinical Neuroanatomy, 8th ed.

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