Overview
This lecture covers the key posterior thoracic muscles that move the pectoral girdle, including their origins, insertions, innervations, actions, and blood supply.
Posterior Thoracic Muscles
- The main posterior thoracic muscles are the trapezius, levator scapulae, rhomboid major, and rhomboid minor.
- These muscles primarily act on the pectoral girdle (shoulder region).
Trapezius Muscle
- The trapezius is a large triangular muscle covering the upper back and neck.
- Originates from the occipital bone and spinous processes of thoracic vertebrae T1–T12.
- Inserts on the lateral third of the clavicle, acromion, and scapular spine.
- Innervated by the spinal accessory nerve and cervical nerves C3–C4.
- Actions include rotation, retraction, elevation, and depression of the scapula and clavicle; also extends the neck and stabilizes the shoulder.
Levator Scapulae
- Originates from the transverse processes of cervical vertebrae C1–C4.
- Inserts on the medial border of the scapula above the scapular spine.
- Innervated by the dorsal scapular nerve and cervical spinal nerves C3–C5.
- Elevates the scapula medially and rotates it downward.
Rhomboid Major
- Originates from the spinous processes of thoracic vertebrae T2–T5.
- Inserts on the medial border of the scapula below the scapular spine.
- Innervated by the dorsal scapular nerve.
- Elevates and adducts (draws together) the scapula, rotates it downward, and stabilizes the scapula.
- Blood supply comes from the dorsal scapular artery.
Rhomboid Minor
- Originates from the spinous processes of cervical vertebra C7 and thoracic vertebra T1.
- Inserts on the medial border of the scapula at the level of the scapular spine.
- Innervated by the dorsal scapular nerve.
- Elevates and adducts the scapula, rotates it downward, and acts synergistically with rhomboid major.
- Blood supply from dorsal scapular artery.
Key Terms & Definitions
- Pectoral girdle — the set of bones connecting the upper limb to the axial skeleton.
- Origin — the fixed attachment point of a muscle.
- Insertion — the movable attachment point of a muscle.
- Innervation — the nerve supply to a muscle.
- Adduct — to move a limb toward the body's midline.
- Synergistic action — muscles working together to perform the same action.
Action Items / Next Steps
- Review the anatomy diagrams of the posterior thoracic muscles and their attachment points.
- Memorize the origin, insertion, innervation, and actions of each muscle.