Back Muscles - Extrinsic (Superficial)
The muscles of the back can be broadly separated into intrinsic and extrinsic groups, based on their embryological origins and functional roles.
The extrinsic muscles of the back stabilize and also move the pectoral girdle and humerus.
The muscles of the superficial back are symmetrically paired, and trapezius lies superficially over the others.
Actions on the Scapula:
When we adduct the scapula, we bring it closer to the midline.
When we rotate the scapula, we "spin" the bone on the back, bringing the bottom of the scapula upwards, or, vice versa, we bring the top of the scapula downwards.
When we elevate the scapula, we bring it closer to our ears – think of shrugging.
And, when we depress the scapula, we bring the bone downward on our backs.
Trapezius:
Originates on the skull (the external occipital protuberance, superior nuchal line) and the spines and connective tissues of C7-T12.
Inserts on the lateral 1/3rd of the clavicle, and on the spine and acromion of the scapula.
Because the fibers of trapezius are convergent, trapezius adducts, rotates, elevates, or depresses the scapula, depending on which fibers contract.
Levator scapulae:
Originates on the transverse processes of vertebrae C1-C4.
Inserts on the medial border of the scapula.
Levator scapulae elevates and rotates the scapula.
Rhomboid minor:
Originates on the spines of vertebrae C7-T1.
Inserts on the scapula at the medial border, adjacent to its spine.
Rhomboid minor adducts the scapula.
Rhomboid major
Originates on the spines of vertebrae T2-T5.
Inserts on the medial border of the scapula.
Rhomboid major adducts the scapula.
Latissimus dorsi
Originates on the spines of vertebrae T7-T12, the thoracolumbar fascia (which overlies the lumbar vertebrae and sacrum), ribs 9-12, the iliac crest (of the ilium), and the inferior scapula.
Inserts on the floor of the bicipital groove of the humerus.
Latissimus dorsi adducts, extends, and medially rotates the humerus, and also depresses the scapula.
Review Intrinsic Muscles:
Superficial & Intermediate Layers
Deep & Minor Layers