Muscle Origin Insertion Action
Scalenus anterior Transverse process of C3-C6 Suuperior surface of first rib Unilateral: flexes and rotates cervical spine to opposite side; Bilateral: flexes neck; raises first rib
Scalenus medius Transverse process of C2-C7 Superior surface of first rib behind subclavian groove Unilatera: Lateral flexion; rotates cervical spine in opposite direction; Bilateral: flexes neck; raises first rib
Scalenus posterior Transverse process of C4-c6 Outer surface of second rib unilateral: lateral flexion; rotates cervical in opposite direction; Bilateral: flexes neck; raises second rib
Sternocleidomastoid Sternal head:anterior part of manubrium; Clavicular head: medial 1/3 of clavicle lateral surface of mastoid process; lateral half of occipital bone Unilateral: head towards shoulder (lateral flexion?); Bilateral: flexes head
Rectus Abdominis pubic crest and symphysis pubis Costal cartilage of fifth and seventh rib; side of xiphoid process Flexion and lateral flexion of trunk: supports organs anteriorly; anterior support for lumbar spine; prevents anterior tilting of pelvis with aid of glutes and hamstrings decreasing lordosis
external abdominal oblique External surfaces and inferior borders of 5-12th ribs Linea alba; anterior half of iliac crest Unilateral: rotates trunk to opposite side, lateral flexion; Bilateral: flexes trunk; anterior support to spine; anterior stabilization of pelvis decreasing lordosis; forces expiration
Internal abdominal oblique (anterior) anterior 1/3 of medial iliac crest Crest of pubis; linea alba Unilateral: rotates trunk to same side, lateral flexion of trunk; Bilateral: flexes vertebrae; supports and compresses abdominals; forced expiration
Internal abdominal oblique (lateral) Medial 1/3 of iliac crest Inferior borders of 10-12th ribs Unilateral: moves thorax and pelvis laterall, rotation of trunk on fixed pelvis towards side of contraction; Bilateral: flexes trunk on pelvis