Muscle
Trapezius
Superficial back, scapular stabiliser
High-yield
Only muscle innervated by cranial nerve XI (spinal accessory) among the scapular movers; test by shrugging against resistance.
Overview
A large superficial triangular muscle of the upper back and neck that suspends and rotates the scapula. Its upper, middle, and lower fibres act in different directions.
Reference facts
- Origin
- Medial third of superior nuchal line, external occipital protuberance, nuchal ligament, and spinous processes of C7-T12
- Insertion
- Lateral third of clavicle, acromion, and spine of the scapula
- Action
- Elevates (upper), retracts (middle), and depresses (lower) the scapula; upper and lower fibres together rotate the glenoid cavity upward
- Innervation
- Spinal accessory nerve (CN XI); proprioception via C3-C4
- Blood supply
- Transverse cervical artery (superficial branch)
Clinical correlation
CN XI injury (e.g., posterior triangle surgery) causes shoulder droop and weak overhead abduction.
Frequently asked questions
What does the trapezius do?
The trapezius elevates (upper), retracts (middle), and depresses (lower) the scapula; upper and lower fibres together rotate the glenoid cavity upward.
What nerve innervates the trapezius?
The trapezius is innervated by the spinal accessory nerve (CN XI); proprioception via C3-C4.
Where does the trapezius attach?
The trapezius originates from the medial third of superior nuchal line, external occipital protuberance, nuchal ligament, and spinous processes of C7-T12 and inserts on the lateral third of clavicle, acromion, and spine of the scapula.
What is the blood supply of the trapezius?
The trapezius is supplied by the transverse cervical artery (superficial branch).