The abdominal internal oblique muscle, also internal oblique muscle or interior oblique, is an abdominal muscle in the

abdominal wall In anatomy, the abdominal wall represents the boundaries of the abdominal cavity. The abdominal wall is split into the anterolateral and posterior walls. There is a common set of layers covering and forming all the walls: the deepest being the vi ...

that lies below the

external oblique muscle The abdominal external oblique muscle (also external oblique muscle or exterior oblique) is the largest and outermost of the three flat abdominal muscles of the lateral anterior abdomen. Structure The external oblique is situated on the lateral ...

and just above the

transverse abdominal muscle The transverse abdominal muscle (TVA), also known as the transverse abdominis, transversalis muscle and transversus abdominis muscle, is a muscle layer of the anterior and lateral (front and side) abdominal wall, deep to (layered below) the inter ...

Structure

Its fibers run perpendicular to the

, beginning in the

thoracolumbar fascia The thoracolumbar fascia (lumbodorsal fascia or thoracodorsal fascia) is a complex, multilayer arrangement of fascial and aponeurotic layers forming a separation between the paraspinal muscles on one side, and the muscles of the posterior abdomina ...

of the lower back, the anterior 2/3 of the

iliac crest The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the posterio ...

(upper part of hip bone) and the lateral half of the

inguinal ligament The inguinal ligament (), also known as Poupart's ligament or groin ligament, is a band running from the pubic tubercle to the anterior superior iliac spine. It forms the base of the inguinal canal through which an indirect inguinal hernia may ...

. The muscle fibers run from these points superomedially (up and towards midline) to the muscle's insertions on the inferior borders of the 10th through 12th ribs and the linea alba. In males, the cremaster muscle is also attached to the internal oblique.

Nerve supply

The internal oblique is supplied by the lower

intercostal nerves The intercostal nerves are part of the somatic nervous system, and arise from the anterior rami of the thoracic spinal nerves from T1 to T11. The intercostal nerves are distributed chiefly to the thoracic pleura and abdominal peritoneum, and dif ...

, as well as the iliohypogastric nerve and the

ilioinguinal nerve The ilioinguinal nerve is a branch of the first lumbar nerve (L1). It separates from the first lumbar nerve along with the larger iliohypogastric nerve. It emerges from the lateral border of the psoas major just inferior to the iliohypogastric, ...

Function

The internal oblique performs two major functions. Firstly as an accessory muscle of respiration, it acts as an antagonist (opponent) to the diaphragm, helping to reduce the volume of the chest cavity during

exhalation Exhalation (or expiration) is the flow of the breathing, breath out of an organism. In animals, it is the movement of air from the lungs out of the airways, to the external environment during breathing. This happens due to elastic properties of ...

. When the diaphragm contracts, it pulls the lower wall of the chest cavity down, increasing the volume of the lungs which then fill with air. Conversely, when the internal obliques contract they compress the organs of the abdomen, pushing them up into the diaphragm which intrudes back into the chest cavity reducing the volume of the air-filled lungs, producing an exhalation. Secondly, its contraction causes ipsilateral rotation and side-bending. It acts with the

of the opposite side to achieve this torsional movement of the trunk. For example, the right internal oblique and the left external oblique contract as the torso flexes and rotates to bring the left shoulder towards the right hip. For this reason, the internal obliques are referred to as "same-side rotators."

Additional images

File:Gray388.png, Diagram of a transverse section of the posterior abdominal wall, to show the disposition of the lumbodorsal fascia. File:Gray399.svg, Diagram of sheath of Rectus. File:Gray400.png, Diagram of a transverse section through the anterior abdomina wall, below the linea semicircularis. File:Gray545.png, Femoral sheath laid open to show its three compartments. File:LumbarTriangle.jpg, Lumbar triangle File:Slide10hel.JPG, Internal abdominal oblique muscle.Anterior abdominal wall.Deep dissection.Anterior view

References

* Moore, Keith L; & Dalley Arthur R (2006). ''Clinically Oriented Anatomy'' (5th ed.). Lippincott Williams and Wilkins. .
Abdominal
unm.edu

External links