Which cranial nerve is responsible for shoulder shrugging?

The cranial nerve responsible for shoulder shrugging is the accessory nerve, also known as cranial nerve XI (CN XI). This nerve innervates the sternocleidomastoid and trapezius muscles. The trapezius muscle plays a crucial role in elevating the shoulders, allowing for the movement commonly referred to as a shoulder shrug.

When the trapezius contracts, it elevates the scapula, which in turn raises the shoulders. The accessory nerve emerges from the upper spinal cord and travels upward to innervate these muscles, making it essential for performing shoulder movements, including shrugging.

In contrast, the other options do not serve this function. The phrenic nerve primarily controls diaphragm movement for breathing, while the vagus nerve is involved in autonomic control of heart and digestive functions. The facial nerve mainly innervates muscles involved in facial expressions, rather than muscles responsible for shoulder movement.