Muscles of the Abdominal Wall

Study Notes

External oblique muscle originates from the inferior eight ribs and inserts into the linea alba and iliac crest, acting together to compress the abdomen and flex the vertebral column, and acting singly to laterally flex the vertebral column, with nerve supply from the lower seven intercostal nerves and iliohypogastric nerves.
Internal oblique muscle originates from the iliac crest, inguinal ligament, and inserts into the linea alba and cartilage of 8-10 ribs, with nerve supply from the last three intercostal nerves, iliohypogastric, and ilioinguinal nerves.
Transverse abdominis muscle originates from the iliac crest, inguinal ligament, and lower ribs, and inserts into the linea alba and pubic bone, compressing the abdomen, with nerve supply from the last five intercostal nerves, iliohypogastric, and ilioinguinal nerves.
Rectus abdominis muscle originates from the pubic crest and symphysis pubis, and inserts into the xiphoid process and cartilage of fifth to seventh ribs, compressing the abdomen, aiding in defecation, urination, forced exhalation, and childbirth, and flexing the vertebral column, with nerve supply from the last six intercostal nerves.
Quadratus lumborum muscle originates from the iliolumbar ligament, iliac crest, and inserts into the inferior border of the last rib, transverse process of vertebrae (L1-L4), flexing the vertebral column laterally and depressing the last rib, with nerve supply from the lumbar nerves.

The muscles of the back play a crucial role in maintaining upright body posture.
These muscles are grouped on either side of the vertebral column, extending from the occiput to the sacrum.
The upper muscles extend the neck.
The lower muscles, including the erector spinae, straighten the spine.
In the lumbar region, the muscles form a large aponeurosis, the lumbar fascia.