Sternocleidomastoid origin: manubrium Insertion: mastoid process Sternocleidomastoid Action Bilaterally: cervical flexion, head extension Unilaterally: Contralateral head rotation, itsilateral neck flexion Splenius group (capitis and cervicis) O: Capitis: nuchal ligament and spinous processes of C7-T4 I: Capitis: mastoid process and occipital bone O: Cervicis: spinous processes of T3-T6 I: Cervicis: transverse processes of C1-C3 Action of splenius group Bilaterally: cervical extension and head extension Unilaterally: ipsilateral head rotation, ipsilateral neck flexion Multifidus and Rotatores O: sacrum and transverse processes of vertebrae I: spinous processes of superior vertebrae Action of Multifidus and rotatores Bilaterally: spinal extension and stabilization Unilaterally: contralateral spinal rotation Interspinales O: spinous processes of respective vertebrae I: spinous processes of superior vertebrae action of interspinales Spinal extension and stabilization Intertransversarii O: Tubercles of transverse processes of each vertebra I: Tubercles of transverse processes of next vertebra Action of intertransversarii Ipsilateral spinal flexion Erector spinae O: Iliocostalis/longissimus: medial iliac crest and thoracolumbar aponeurosis O: Spinalis: nuchal ligament All: various spinous and transverse processes I: Spinalis: occipital bone I: All: various spinous and transverse processes of superior vertebrae Action of erector spinae Spinal extension, ipsilateral spinal flexion, contralateral spinal rotation Quadratus Lumborum O: Posterior iliac crest I: Inferior of 12th rib and transverse processes of L1-L4 Action of Quadratus Lumborum Bilaterally: lumbar extension, anterior pelvic rotation, and pelvic/lumbar stabilization Unilaterally: ipsilateral lumbar flexion and contralateral pelvic rotation Rectus Abdominis O: Pubic crest I: Cartilage of 5th-7th ribs and xiphoid process Action of the rectus abdominis A: Lumbar flexion, posterior pelvic rotation External Obliques O: Lateral border of 5th-12th ribs I: Anterior iliac crest, pubic crest, and fascia of rectus abdominis Action of External obliques Bilaterally: lumbar flexion and posterior pelvic rotation Unilaterally: ipsilateral lumbar flexion and contralateral lumbar/pelvic rotation internal Obliques O: Inguinal ligament, anterior iliac crest, and lumbar fascia I: Cartilage of 8th-10th ribs and fascia of rectus abdominis Action of internal obliques Bilaterally: lumbar flexion and posterior pelvic rotation Unilaterally: ipsilateral lumbar flexion, ipsilateral lumbar rotation, and contralateral pelvic rotation Transversus abdominis O: Inguinal ligament, iliac crest, cartilage of 7th-12th ribs, and lumbar fascia I: Pubic crest and iliopectineal line Action of transverse abdominis Compresses abdomen Internal intercostals O: Superior border of rib I: Inferior border of superior rib Action of external intercostals Elevation of ribs (during all inspiration) Diaphragm O: Xiphoid process, cartilage of 6th-12th ribs, and lumbar vertebrae I: Central tendon of diaphragm Action of diaphragm Depresses bottom wall of thoracic cavity (during all inspiration) Trapezius O: Occipital bone and spinous processes of C7-T12 I: Lateral clavicle, acromion process, scapula spine Action of the trapezius Upper: scapula elevation, head extension Middle: scapula elevation, retraction, and upward rotation Lower: scapula depression, retraction, and upward rotation Levator Scapula O: Transverse processes of C1-C4 I: Vertebral border superior of scapula spine Action of the levator scapula A: Scapula elevation Rhomboid major O: Major: spinous process of T2-T5 I: Major: vertebral border inferior of scapula spine Rhomboid minor O: Minor: spinous processes of C7-T1 I: Minor: vertebral border at scapula spine Action of the Rhomboid minor scapula retraction, elevation, and downward rotation Pectoralis Minor O: Anterior surface of 3rd-5th ribs I: Coracoid process of scapula Action of the pectorals Minor Scapula protraction, depression, and downward rotation Serratus anterior O: Lateral border of 1st-9th ribs I: Vertebral border of scapula Action of serrates anterior Scapula protraction and upward rotation Subclavius O: Sternal end of 1st rib I: Inferior surface of clavicle Action of the subclavius Scapula protraction and depression, and stabilization of sternoclavicular joint Supraspinatus O: Supraspinous fossa of scapula I: Greater tubercle of humerus Action of the Supraspinatus Shoulder abduction and superior stabilization of humerus Infraspinatus O: Infraspinous fossa of scapula I: Greater tubercle of humerus Action of the infraspinatus External rotation and posterior stabilization of humerus Teres Minor O: Axillary border of scapula I: Greater tubercle of humerus Action of the teres minor External rotation and posterior stabilization of humerus Subscapularis O: Subscapular fossa of scapula I: Lesser tubercle of humerus Action of the subscapularis Internal rotation and anterior stabilization of humerus