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Anatomy Muscles 275-300


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Rhomboids action
Act together (and with middle trapezius fibers) to retract scapula, thus “squaring shoulders”; rotates downward (as when arm is lowered against resistance; e.g., paddling a canoe); stabilize scapula
Rhomboids innervation
Dorsal scapular nerve (C5)
Trapezius origin and insertion
origin: Occipital bone, ligamentum nuchae, and spines of C7 and all thoracic vertebrae; insertion: A continuous insertion along acromion and spin of scapula and lateral third of clavicle
Levator Scapulae action
Elevates/adducts scapula in concert with superior fibers of trapezius; tilts
Levator Scapulae innervation
Cervical spinal nerves and dorsal scapular nerve (C3-C5)
Subclavius origin and insertion
origin: Costal cartilage of rib 1; insertion: Groove on inferior surface of clavicle
Trapezius action
Stabilizes, raises, retracts, and rotates scapula; middle fibers retract (adduct) scapula; superior fibers elevate scapula or can help extend head; inferior fibers depress scapula (and shoulder)
Trapezius innervation
Accessory nerve (C3, C4)
Serratus Anterior origin and insertion
origin: By a series of muscle slips from ribs 1-8 (or 9); insertion: Entire anterior surface of vertebral border of scapula
Subclavius action
Helps stabilize and depress pectoral girdle; paralysis produces no obvious effects
Subclavius innervation
Nerve to Subclavius (C5, C6)
Pectoralis Minor origin and insertion
origin: Anterior surfaces of ribs 3-5; insertion: Coracoid process of Scapula
Serratus Anterior action
Prime mover to protract and hold scapula against chest wall; rotates scapula so that its inferior angle moves laterally and upward; raises point of shoulder; important role in abduction and raising of arm and in horizontal arm movements (pushing, punching); called “boxer’s muscle”
Serratus Anterior innervation
Long Thoracic Nerve (C5-C7)
Diaphragm origin and insertion
origin: Inferior border of rib cage and sternum, costal cartilages of last six ribs and lumbar vertebrae; insertion: Central tendon
Pectoralis Minor action
With ribs fixed, draws scapula forward and downward; with scapula fixed, draws rib cage superiorly
Pectoralis Minor innervation
Medial Pectoral Nerve (C6-C8)
Internal Intercostals origin and insertion
origin: Superior border of rib below; insertion: Inferior border (costal groove) of rib above
Diaphragm action
Prime mover of inspiration; flattens on contraction, increasing vertical dimensions of thorax; when strongly contracted, dramatically increases intra-abdominal pressure
Diaphragm innervation
Phrenic nerves
External Intercostals origin and insertion
origin: Inferior border of rib above; insertion: Superior border of rib below
Internal Intercostals action
With 12th ribs fixed by quadratus lumborum, muscles of posterior abdominal wall and oblique muscles of the abdominal wall, draw ribs together and depress rib cage; aid in expiration; antagonistic to external intercostals
Internal Intercostals innervation
Intercostal nerves
Quadratus Lumborum origin and insertion
origin: Iliac crest and iliolumbar fascia; insertion: Transverse processes of upper lumbar vertebrae and lower margin of 12th rib
External Intercostals action
With first ribs fixed by scalene muscles, pull ribs toward one another to elevate rib cage; aids in inspiration; synergists of diaphragm

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