|Origin||Occipital bone, Ligamentum nuchae, C7-T1 – 3 segments|
|Insertion||1. Descending fibers – Lateral 1/3 of Clavicle|
2. Transverse fibers – Acromion
3. Ascending fibers – Spine of the Scapula
|Nerve supply||Spinal Accessory nerve|
|Actions||elevates, retracts, laterally rotates and depresses the scapula|
Trapezius Origin and Insertions – Image modified from BodyParts3D, © The Database Center for Life Science licensed under CC Attribution-Share Alike 2.1 Japan
The upper fibers elevate (pull it up) the scapulae, the middle fibers retract (pull it towards spine) the scapulae, and the lower fibers depress (pull it down) the scapulae
Spinal accessory nerve (Cranial Nerve 11) supplies sternocleidomastoid also.
TEST – shrug the shoulder against resistance to test accessory nerve.
Weakness of both the trapezius and sternocleidomastoid muscles indicates the Nerve damage closer to the accessory nerve exit / the base of the skull (More about nerve exits in CNS module).
But if only trapezius muscle is weak, that indicates damage more distally, as in posterior triangle of the neck.
Check previous lesson for Pectoralis Minor and Next lesson for Latissimus dorsi muscle.