Transversus abdominis muscle

At a glance

English

Transversus abdominis muscle

Latin (TA2)

Musculus transversus abdominis

System

Muscle

Region

Trunk

Side

Paired, left and right

About the transversus abdominis muscle

Transversus abdominis forms the innermost of the three flat muscle layers of the side and front of the abdomen, lying beneath the internal oblique. Its name describes its fibres, which run mostly horizontally around the trunk. Inside it lies only the transversalis fascia and the peritoneum.

The muscle has a long origin that encircles the lower trunk. It arises from the inner faces of the lower six costal cartilages, where its slips interlock with those of the diaphragm, from the thoracolumbar fascia at the back, from the iliac crest's inner lip over its front three-quarters and from the inguinal ligament's outer third. From here the fibres pass forward into a broad aponeurosis. The line where muscle gives way to aponeurosis is curved and is called the semilunar line. Above the arcuate line the aponeurosis lies behind rectus abdominis as part of the posterior rectus sheath; below it, the aponeurosis passes in front of rectus. All of it ends in the linea alba. The lowest fibres arch downward and join the internal oblique to form the conjoint tendon on the pubic crest and pectineal line.

Contraction pulls the abdominal wall inward and squeezes the abdominal organs, raising pressure inside the abdomen. This helps in forced breathing out, coughing, vomiting and emptying of the bowel and bladder. Acting with the deep muscles of the back and the pelvic floor, it tightens the thoracolumbar fascia and stiffens the lumbar spine and pelvis just before and during movements of the limbs and lifting. This bracing role has made it a focus of core-training programmes, though research has not shown that its function predicts or explains low back pain.

It is supplied by the anterior rami of the seventh to twelfth thoracic nerves and by the iliohypogastric and ilioinguinal nerves (L1), which run in the plane between it and the internal oblique. That plane is targeted in the transversus abdominis plane block, a local anaesthetic technique for abdominal surgery. Its blood comes from the lower posterior intercostal and subcostal arteries, the epigastric arteries and the deep circumflex iliac artery.

Attachments, action and supply

Origin

Inner surfaces of the lower six costal cartilages, thoracolumbar fascia, anterior three-quarters of the iliac crest and outer third of the inguinal ligament.

Insertion

Linea alba through its aponeurosis, and the pubic crest and pectineal line through the conjoint tendon.

Action

Compresses the abdomen and raises intra-abdominal pressure; stiffens the lumbar spine and pelvis through the thoracolumbar fascia.

Nerve supply

Thoracoabdominal nerves (T7-T11), subcostal nerve (T12), iliohypogastric and ilioinguinal nerves (L1).

Blood supply

Lower posterior intercostal and subcostal arteries, superior and inferior epigastric arteries and the deep circumflex iliac artery.