A deficit in which action would indicate impairment of the cranial nerve XI?

A deficit in which action would indicate impairment of the cranial nerve XI?

• A. Shrugging shoulders
• B. Smiling symmetrically
• C. Blinking eyes
• D. Smelling odors

Answer: (A)

Cranial nerve XI, the spinal accessory nerve, supplies the trapezius and sternocleidomastoid muscles. A deficit here weakens these muscles, especially the trapezius, which is responsible for elevating the shoulders in a shrug. So testing shoulder shrug against resistance reveals weakness indicative of CN XI impairment. The other actions involve different nerves: smiling symmetrically mainly tests facial nerve function, blinking involves the facial nerve as well, and smelling odors assesses the olfactory nerve.

Cranial nerve XI, the spinal accessory nerve, supplies the trapezius and sternocleidomastoid muscles. A deficit here weakens these muscles, especially the trapezius, which is responsible for elevating the shoulders in a shrug. So testing shoulder shrug against resistance reveals weakness indicative of CN XI impairment. The other actions involve different nerves: smiling symmetrically mainly tests facial nerve function, blinking involves the facial nerve as well, and smelling odors assesses the olfactory nerve.