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Muscles of the trunk
Origin, insertion, and action.
| Muscle | Origin | Insertion | 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
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