Muscle
Trapezius
Positions the scapula for shoulder movement
High-yield
Upper and lower fibers cooperate in upward scapular rotation. The spinal accessory nerve supplies motor function; cervical branches carry sensory information including position sense.
Overview
Trapezius spreads across the back of the neck and upper thorax to the clavicle and scapula. Its upper, middle and lower regions pull in different directions, positioning the blade as the arm moves.
Reference facts
- Origin
- Medial superior nuchal line, external occipital protuberance, nuchal ligament and spinous processes C7–T12
- Insertion
- Lateral third of the clavicle, acromion and scapular spine
- Action
- Upper fibers elevate, middle fibers retract and lower fibers depress the scapula; upper and lower parts assist upward rotation
- Innervation
- Motor: spinal accessory nerve (CN XI); sensory/proprioceptive input: mainly C3–C4
- Blood supply
- Mainly transverse cervical arterial supply, with dorsal scapular and intercostal contributions
Clinical correlation
Injury to the spinal accessory nerve in the posterior neck triangle can weaken trapezius, causing shoulder droop and difficulty with overhead movement. The nerve may be vulnerable during procedures in this region.
Frequently asked questions
What does the trapezius do?
Upper fibers elevate, middle fibers retract and lower fibers depress the scapula; upper and lower parts assist upward rotation.
What nerve innervates the trapezius?
Motor: spinal accessory nerve (CN XI); sensory/proprioceptive input: mainly C3–C4.
Where does the trapezius attach?
Origin: Medial superior nuchal line, external occipital protuberance, nuchal ligament and spinous processes C7–T12. Insertion: Lateral third of the clavicle, acromion and scapular spine.
What is the blood supply of the trapezius?
Mainly transverse cervical arterial supply, with dorsal scapular and intercostal contributions.