Which nerve innervates the trapezius?

The trapezius muscle is primarily innervated by cranial nerve XI, also known as the spinal accessory nerve. This nerve is responsible for supplying motor function to the trapezius, which plays a critical role in moving the shoulder blades (scapulae) and assisting in neck movements.

Cranial nerve XI originates in the brainstem and emerges from the upper spinal cord, specifically from the cervical region, which allows it to effectively reach the trapezius muscle. This innervation enables actions such as shoulder elevation, retraction, and rotation.

Understanding the function of the trapezius and its specific nerve supply is essential for professionals in fields such as anatomy, physical therapy, and medicine, as it informs assessments and treatment for shoulder pathologies or injuries that might interfere with shoulder movement and stability.