What is the function of the spinal accessory nerve?

The spinal accessory nerve primarily serves the function of innervating the upper trapezius and sternocleidomastoid muscles, which are crucial for neck movement and shoulder elevation. This nerve is responsible for enabling actions such as shrugging the shoulders and turning the head from side to side. Its role is essential in movements associated with posture and upper limb support, which highlights its importance in motor control of specific muscles in the upper body.

The other choices focus on functions attributed to different cranial nerves. For instance, facial expression and taste are functions associated with the facial nerve, while eye movement is controlled by a group of other cranial nerves, particularly the oculomotor, trochlear, and abducens nerves. Smell perception is governed by the olfactory nerve, making all other options distinct from the role of the spinal accessory nerve.