External Oblique Muscle; Origin, Nerve Supply, Fuctions

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. The external oblique is situated on the lateral and anterior parts of the abdomen. It is broad, thin, and irregularly quadrilateral, its muscular portion occupying the side, its aponeurosis the anterior wall of the abdomen. In most humans (especially females), the oblique is not visible, due to subcutaneous fat deposits and the small size of the muscle.

All You Need To Know About External Oblique Muscle

Origin – the outer surface of the shaft of the lower 8 ribs. The internal obliques originate on the inguinal ligament (a ligament that runs from the anterior iliac spine to the pubic bone) and the anterior iliac crest. The external obliques originate on the lower 8 ribs.

Insertion – upper aponeurotic fibers to the whole length of the linea alba and extends to the pubic crest and the pectineal line; lower fleshy fibers to the outer lip of the anterior end of the iliac crest. The internal obliques insert onto the costal cartilages of the lower 4 ribs, the abdominal aponeurosis (a superficial sheet of connective tissue over the abdomen), and the linea alba. (The linea alba is a fibrous band of connective tissue that runs from the xiphoid process to the pubic symphysis.) The external obliques insert onto the abdominal aponeurosis, the linea alba, the iliac crest, and the pubic bone.

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Nerve Supply of External Oblique Muscle

• Innervation – segmental supply by lower 6 thoracic nerves
• The external oblique muscle is supplied by ventral branches of the lower six thoracoabdominal nerves and the subcostal nerve on each side.

Blood Supply of External Oblique Muscle

External oblique has a profuse blood supply. The following arteries are involved;

• Lower posterior intercostal and subcostal arteries
• Superior and Inferior epigastric arteries
• Superficial and deep circumflex iliac arteries
• Posterior lumbar arteries
• The cranial portion of the muscle is supplied by the lower intercostal arteries, whereas the caudal portion is supplied by a branch of either the deep circumflex iliac artery or the iliolumbar artery.

Functions of External Oblique Muscle

• Action contributes to forming the anterior abdominal wall and the action is along with the other abdominal wall muscles
• The external oblique functions to pull the chest downwards and compress the abdominal cavity, which increases the intra-abdominal pressure as in a Valsalva maneuver. It also performs ipsilateral (same side) side-bending and contralateral (opposite side) rotation. So the right external oblique would side bend to the right and rotate to the left. The internal oblique muscle functions similarly except it rotates ipsilaterally.

Besides twisting the trunk of the body, the external oblique muscles are also responsible for the movement of the spine, including:

• Pulling the spine forward as the external oblique contracts (like in crunches or sit-ups)
• Stabilizing the core
• Moving the spine in any direction
• Pulling the chest down to compress the abdomen
• Supporting the abdominal wall
• Assisting with forced expiration in breathing
• Bending from side to side

References

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