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

abdominal muscle The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso ...

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 ...

that lies below the external oblique muscle 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 which is deep to (layered below) th ...

Structure

Its fibers run perpendicular to the external oblique muscle, beginning in the

thoracolumbar fascia The thoracolumbar fascia (lumbodorsal fascia or thoracodorsal fascia) is a deep investing membrane throughout most of the posterior thorax and abdomen although it is a thin fibrous lamina in the thoracic region. Above, it is continuous with a simil ...

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 superiolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the poster ...

(upper part of hip bone) and the lateral half of the inguinal ligament. 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 The cremaster muscle is a paired structure made of thin layers of striated and smooth muscle that covers the testis and the spermatic cord in human males. It consists of the lateral and medial parts. Cremaster is an involuntary muscle, responsib ...

is also attached to the internal oblique.

Nerve supply

The internal oblique is supplied by the lower intercostal nerves, as well as the

iliohypogastric nerve The iliohypogastric nerve is a nerve that originates from the lumbar plexus that supplies sensation to skin over the lateral gluteal and hypogastric regions and motor to the internal oblique muscles and transverse abdominal muscles. Structure ...

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, a ...

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 The thoracic cavity (or chest cavity) is the chamber of the body of vertebrates that is protected by the thoracic wall (rib cage and associated skin, muscle, and fascia). The central compartment of the thoracic cavity is the mediastinum. There ...

during

exhalation Exhalation (or expiration) is the flow of the 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 the lungs, ...

. 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 external oblique muscle 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.png, 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