Which nerve innervates trapezius?

Which nerve innervates trapezius?

• A. CN XI (spinal accessory nerve) with C3-C4
• B. CN XII (hypoglossal nerve)
• C. Dorsal scapular nerve
• D. Axillary nerve

Answer: (A)

The key idea is that the trapezius gets its motor supply from the spinal accessory nerve (cranial nerve XI), with proprioceptive input from C3–C4. This nerve pathway brings commands from the nervous system to lift, rotate, and retract the scapula, which matches the actions of the trapezius. The other nerves don’t supply this muscle: the hypoglossal nerve serves the tongue, the dorsal scapular nerve mainly innervates the rhomboids and levator scapulae, and the axillary nerve innervates the deltoid and teres minor. So the spinal accessory nerve with C3–C4 proprioception is the correct innervation for the trapezius.

The key idea is that the trapezius gets its motor supply from the spinal accessory nerve (cranial nerve XI), with proprioceptive input from C3–C4. This nerve pathway brings commands from the nervous system to lift, rotate, and retract the scapula, which matches the actions of the trapezius. The other nerves don’t supply this muscle: the hypoglossal nerve serves the tongue, the dorsal scapular nerve mainly innervates the rhomboids and levator scapulae, and the axillary nerve innervates the deltoid and teres minor. So the spinal accessory nerve with C3–C4 proprioception is the correct innervation for the trapezius.