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Muscles of the trunk

Origin, insertion, and action.

Omohyoid O- superior surface of scapula I- hyoid bone, lower border Depresses and retracts hyoid bone.
Sternocleidomastoid O- manubrium of sternum and medial portion of clavicle I- mastoid process of temporal bone and superior nuchal line of occipital bone Prime mover of active head flexion; simultaneous contraction of both muscles causes neck flexion, generally against resistance as when one raises head when lying on back; acting alone, each muscle rotates head toward shoulder on opposite side and tilts...
Scalenes O- transverse processes of cervical vertebrae I- aterolaterally on first two ribs Elevate first two ribs (aid in inspiration); flex and rotate neck.
Splenius O- ligamentum nuchae, spinous processes of vertebrae C7-T6 I- mastoid process of temporal bone and occipital bone(capitis); transverse processes of C2-C4 vertebrae (cervicis) Act as a group to extend or hyper extend head; when splenius muscles on one side are activated, head is rotated and bent laterally toward same side.
Iliocostalis O- iliac crests (lumborum); inferior 6 ribs (thoracis); ribs 3 to 6 (cervicis) I- angles of ribs (lumborum and thoracis); transverse processes of cervical vertebrae C6-C4 (cervicis) Extend vertebral column, maintain erect posture; acting on one side, bend vertebral column to same side.
Longissimus O- transverse processes of lumbar through cervical vertebrae I- transverse processes of thoracic or cervical vertebrae and to ribs superior to origin as indicated by name; capitis inserts into mastoid process of temporal bone Thoracis and cervicis act together to extend vertebral column and acting on one side, bend it laterally; capitis extends head and turns the face toward same side
Spinalis O- spins of upper lumbar and lower thoracic vertebrae I- spines of upper thoracic and cervical vertebrae Extends vertebral column.
Semispinalis O- transverse processes of C7-T12 I- occipital bone (capitis) and spinous processes of cervical (cervicis) and thoracic vertebrae T1-T4 (thoracis) Extends vertebral column and head and rotates them to opposite side; acts synergistically with sternocleidomastoid muscles of opposite side.
Quadratus lumborum O- iliac crest and lumbar fascia I- transverse processes of upper lumbar vertebrae and lower margin of 12th rib Flexes vertebral column laterally when acting seperately; when pair acts jointly, lumbar spine is extended and 12th rib is fixed; maintains upright posture; asists in forced inspiration.
External intercostals O- inferior border of rib above I- superior border of rib below With first ribs fixed by scalene muscles, pull ribs toward one another to elevate rib cage; aids in inspiration; synergists of diaphragm.
Rectus abdominis O- pubic crest and symphysis I- xiphoid process and costal cartilages of ribs 5-7 Flex and rotate lumbar region of vertebral column; fix and depress ribs, stabilize pelvis during walking, increase intra-abdominal pressure.
Internal oblique O- lumbar fascia, iliac crest, and inguinal ligament I- linea alba, pubic crest, last three or four ribs, and costal margin When pair contract simultaneously, aid rectus abdominis muscles in flexing vertebral column and in compressing abdominal wall and increasing intra-abdominal pressure; acting individually, aid muscles of back in trunk rotation and lateral flexion.
Transversus abdominus O- inguinal ligament lumbar fascia, cartilages of last six ribs; iliac crest I- linea alba, pubic crest Compresses abdominal contents.
Created by: prosesque