Transversus Abdominis
Abdomen · Trunk
The transversus abdominis is the deepest of the three flat muscles of the abdominal wall, named for the horizontal course of its fibres. It arises from the internal surfaces of costal cartilages 7 to 12, the thoracolumbar fascia, the iliac crest, and the lateral part of the inguinal ligament, and its transverse fibres run around the trunk to insert into the linea alba, the pubic crest, and the pecten pubis by way of the conjoint tendon. Because its fibres wrap horizontally like a corset or weightlifting belt, its chief action is to compress and support the abdominal viscera and to raise intra-abdominal pressure, rather than to move the trunk. It is supplied by the thoracoabdominal nerves (T7 to T12) and the first lumbar nerve.
Origin, Insertion, Action & Nerve
Origin
Internal surfaces of costal cartilages 7–12, thoracolumbar fascia, iliac crest, and lateral inguinal ligament
Insertion
Linea alba, pubic crest, and pecten pubis (via conjoint tendon)
Action
Compresses and supports abdominal viscera
Nerve
Thoracoabdominal nerves (T7–T12) and L1
Attachments explained
The Transversus Abdominis is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Internal surfaces of costal cartilages 7–12, thoracolumbar fascia, iliac crest, and lateral inguinal ligament
Insertion
Linea alba, pubic crest, and pecten pubis (via conjoint tendon)
Action & function
When the Transversus Abdominis contracts, it produces the following movement: Compresses and supports abdominal viscera.
As part of the Abdomen group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Transversus Abdominis receives its nerve supply from the Thoracoabdominal nerves (T7–T12) and L1. This nerve carries fibres from spinal segment(s) T7, T12, L1.
Because a muscle can only contract when its nerve is intact, injury to the Thoracoabdominal nerves or to its spinal roots (T7, T12, L1) can weaken or paralyse the Transversus Abdominis, impairing the movements it normally produces (compresses and supports abdominal viscera). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Transversus Abdominis (the OIANS method)
Remember transversus abdominis as the internal corset: its horizontal fibres are unique among the abdominal muscles, and because they encircle the trunk rather than run obliquely, they cannot flex or rotate it but instead squeeze inward. This links it to core stability and to actions that need raised abdominal pressure, such as coughing, straining, and forced expiration.
Place it correctly by depth, deepest of the three flat muscles, so its aponeurosis contributes to the conjoint tendon and the rectus sheath alongside the internal oblique. Sharing the thoracoabdominal nerves and L1 with the other wall muscles, it follows the same segmental supply, which is worth grouping in memory rather than learning each muscle's nerve separately.
Frequently asked questions
Where is the Transversus Abdominis located?
The Transversus Abdominis is a muscle of the Abdomen group, located in the Trunk.
What is the origin of the Transversus Abdominis?
Internal surfaces of costal cartilages 7–12, thoracolumbar fascia, iliac crest, and lateral inguinal ligament
What is the insertion of the Transversus Abdominis?
Linea alba, pubic crest, and pecten pubis (via conjoint tendon)
What movements does the Transversus Abdominis produce?
Compresses and supports abdominal viscera
What nerve supplies the Transversus Abdominis?
Thoracoabdominal nerves (T7–T12) and L1
Is the Transversus Abdominis free to study in OIANS?
The Transversus Abdominis is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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