Muscles of the Chest and Trunk

 Muscle Origin Insertion Action Notes
Intercostals Inferior border of the rib above Superior border of the rib below External Intercostals: draw the ventral part of the ribs upward, increasing thoracic cavity spaceInternal Intercostals: draw the ventral part of the ribs downward, decreasing the space of the thoracic cavity Stabilize the rib cage and assist in respiration.Meat of spare ribs.
Pectoralis major Sternal ½ of clavicle, sternum to 7th rib, aponeurosis of external oblique muscle. Crest of greater tubercle of humerus: Lateral lip of bicipital grove. Clavicular (upper) fibers- flexion of humerusSternocostal (middle and lower) fibers- extension of humerus returning from flexion

Adduction, medial rotation

Forms the anterior wall of axilla.Upper and lower fibers are work in opposite actions making it an antagonist to itself.

Triggerpoints may cause pain, swelling and congestion of lymphatic fluids in breast tissue.

Pectoralis minor Third, fourth and fifth ribs Coracoid process of scapula Tilts scapula forward, depresses and abducts scapula, Pulls shoulder forward when rhomboids are weak
Diaphragm Sternal: inner part of ziphoid processCoastal- inner surface of lower 6 ribs

Lumbar- upper 2-3 lumbar vertebrae

Central tendon Draws central tendon down during inspiration, increases volume of thoracic cavity (increases diameters) Forms floor of thoracic cavity.
Rectus abdominis Crest of the pubis, pubic symphysis Cartilage of the 5th, 6th and 7thribs and ziphoid process Flexes the vertebral column Sometimes origin and insertion are reversed
External obliques Lower eight ribs (5-12) Anterior part of iliac crest, abdominal aponeurosis to linea alba Bilaterally- flexes thorax and compresses abdominal contentsUnilaterally- laterally flexes spine and rotates spine to opposite side Interdigitates with serratus anterior. Place hands on hips as if you were reaching into pants pockets to follow directions of fibers (obliquely downward and medialward)
Internal obliques Lateral inguinal ligament, anterior iliac crest, thoracolumbar aponeurosis Cartilage of lower 3-5 ribs (7-12), abdominal aponeurosis to linea alba Bilaterally- flexes the thorax, compresses abdominal contentsUnilaterally- laterally flexes spine and rotates trunk to same side Place hands over abdomen with fingertips on the anterior-superior iliac spine, your fingertips will follow the direction of the fibers (obliquely upward and medialward)
Transverse abdominis Lateral inguinal ligament, anterior iliac crest, thoracolumbar fascia, cartilage of lower 6 ribs (7-12) Abdominal aponeurosis to linea alba Compresses abdominal contents Deepest layer of abdominals: runs horizontally medialward
Quadratus lumborum Posterior iliac crest, iliolumbar ligament Last rib, transverse processes of L1-L4 Bilaterally- extends the spineUnilaterally- lateral flexion of lumbar spine

With spine fixed-elevates hip (hikes hip up).

Holds 12th rib against the pull of the diaphragm

Accessory breathing muscle. Spinal stabilizer

Composed of three groups of fibers: Iliocostal fibers run from medial upper crest of ilium and iliolumbar ligament upward to 12th rib (vertical) Iliolumbar fibers run from the ilium to the transverse processes of L1-L4Lumbocostal fibers fun from the 12th rib to transverse processes of lumbar vertebrae

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