Muscles of the Abdominal Wall

Study Notes

External oblique muscle: originates from inferior eight ribs, inserts into linea alba and iliac crest, and acts to compress abdomen and flex vertebral column; also laterally flexes vertebral column (especially lumbar vertebrae) when acting singly; innervated by lower seven intercostal nerves and iliohypogastric nerves.
Internal oblique muscle: originates from iliac crest and inguinal ligament, inserts into linea alba and cartilage of 8-10 ribs, and acts to compress abdomen; innervated by last three intercostal nerves, iliohypogastric, and ilioinguinal nerves.
Transverse abdominis muscle: originates from iliac crest, inguinal ligament, and lower ribs, inserts into linea alba and pubic bone, and acts to compress abdomen; innervated by last five intercostal nerves, iliohypogastric, and ilioinguinal nerves.
Rectus abdominis muscle: originates from pubic crest and symphysis pubis, inserts into xiphoid process and cartilage of fifth to seventh ribs, and acts to compress abdomen.
Quadratus lumborum muscle: originates from iliolumbar ligament and iliac crest, inserts into inferior border of last rib and transverse process of vertebrae (L1-L4), and acts to compress abdomen, aid in defecation, urination, and forced exhalation, and flex vertebral column (especially lumbar vertebrae); innervated by last six intercostal nerves and lumbar nerves.

The muscles of the back play an important role in maintaining upright body posture.
The muscles of the back can be grouped into several groups on either side of the vertebral column, extending from the occiput to the sacrum.
The upper muscles extend the neck, while the lower muscles, including the erector spinae, straighten the spine.
In the lumbar region, the muscles form a large aponeurosis called the lumbar fascia.