Back Muscles – Origin, Insertion, Action & Innervation Practice Test

The main idea is that the trapezius receives motor input from the spinal accessory nerve (cranial nerve XI) and sensory/proprioceptive input from C3-C4 spinal nerves. The spinal accessory nerve provides the actual signals to contract the trapezius, while the C3-C4 nerves deliver proprioceptive feedback about position and movement. Other nerves listed target different muscles: the thoracodorsal nerve to latissimus dorsi, the dorsal scapular nerve to rhomboids (and sometimes levator scapulae), and the long thoracic nerve to serratus anterior. Therefore, the combination of cranial nerve XI and C3-C4 best matches the trapezius’ innervation.