Rectus abdominis muscle

Rectus abdominis
The human rectus abdominis muscle.
Latin	musculus rectus abdominis
Gray's	subject #118 415
Origin	pubis
Insertion	Costal cartilage of ribs 5-7, xiphoid process of sternum
Artery	inferior epigastric artery
Nerve	segmentally by thoraco-abdominal nerves (T7 to T12)
Actions	Flexion of the lumbar spine
Antagonist	Erector spinae

The rectus abdominis muscle, also known as the "abs," is a paired muscle running vertically on each side of the anterior wall of the human abdomen, as well as that of some other mammals. There are two parallel muscles, separated by a midline band of connective tissue called the linea alba ("white line"). It extends from the pubic symphysis, pubic crest and pubic tubercle inferiorly, to the xiphoid process and costal cartilages of ribs V to VII superiorly.

It is contained in the rectus sheath, which consists of the aponeuroses of the lateral abdominal muscles.

Three, and sometimes four, bands of connective tissue called the tendinous intersections traverse the rectus abdominus, which separate it into six or eight distinct muscle bellies, respectively. The appearance of these segments has led to the rectus abdominus also being called the "six-pack."

Rectus abdominis sheath as visible on human dissection

Function

The rectus abdominis is an important postural muscle. It is responsible for flexing the lumbar spine, as when doing a "crunch". The rib cage is brought up to where the pelvis is when the pelvis is fixed, or the pelvis can be brought towards the rib cage (posterior pelvic tilt) when the rib cage is fixed, such as in a leg-hip raise. The two can also be brought together simultaneously when neither is fixed in space.

The rectus abdominis assists with breathing and plays an important role in respiration when forcefully exhaling, as seen after exercise as well as in conditions where exhalation is difficult such as emphysema. It also helps in keeping the internal organs intact and in creating intra-abdominal pressure, such as when exercising or lifting heavy weights, during forceful defecation or parturition (childbirth).

Blood supply

The rectus abdominis has several sources of arterial blood supply. In reconstructive surgery terms, it is a Mathes and Nahai Type III muscle with two dominant pedicles. First, the inferior epigastric artery and vein (or veins) run superiorly on the posterior surface of the rectus abdominis, enter the rectus fascia at the arcuate line, and serve the lower part of the muscle. Second, the superior epigastric artery, a terminal branch of the internal thoracic artery, supplies blood to the upper portion. Finally, numerous small segmental contributions come from the lower six intercostal arteries as well.

Innervation

The muscles are innervated by thoracoabdominal nerves, which pierce the anterior layer of the rectus sheath.

Rectus abdominis muscle

Location

The rectus abdominis is a long flat muscle, which extends along the whole length of the front of the abdomen, and is separated from its fellow of the opposite side by the linea alba.

The muscle is inserted by three portions of unequal size into the cartilages of the fifth, sixth, and seventh ribs.

The upper portion, attached principally to the cartilage of the fifth rib, usually has some fibers of insertion into the anterior extremity of the rib itself.

Some fibers are occasionally connected with the costoxiphoid ligaments, and the side of the xiphoid process.

Damage

An abdominal muscle strain, also called a pulled abdominal muscle, is an injury to one of the muscles of the abdominal wall. A muscle strain occurs when the muscle is stretched too far. When this occurs the muscle fibers are torn. Most commonly, a strain causes microscopic tears within the muscle, but occasionally, in severe injuries, the muscle can rupture from its attachment.

Animals

A feline rectus abdominis muscle, from a common housecat. This specimen has some remaining fascia and also shows the external obliques.

The rectus abdominis is similar in most vertebrates. The most obvious difference between animal and human abdominal musculature is that in animals, there are a different number of tendinous intersections.

Additional images

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  Anterior surface of sternum and costal cartilages

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  The interfoveolar ligament, seen from in front

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  Diagram of sheath of rectus

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  Diagram of a transverse section through the anterior abdomina wall, below the linea semicircularis

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  The relations of the femoral and abdominal inguinal rings, seen from within the abdomen. Right side

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  Horizontal disposition of the peritoneum in the lower part of the abdomen

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  Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas

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  The left side of the thorax

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  Surface anatomy of the front of the thorax and abdomen

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  Muscles of the trunk

See also

• Divarication of rectus abdominis muscles

External links

• LUC reca
• 168165454 at GPnotebook
• SUNY Figs 04:04-07 – "Muscles of the anterior chest wall with the pectoralis major muscles removed."
• SUNY Labs 18:01-0115 – "Thoracic Wall: The Anterior Thoracic Wall"
• SUNY Figs 35:06-07 – "Incision and reflection of the external abdominal oblique muscle."
• SUNY Figs 35:07-01 – "Incision and reflection of the internal abdominal oblique muscle."
• SUNY Labs 35:10-0100 – "Anterior Abdominal Wall: The Rectus Abdominis Muscle"
• Cross section at UV pembody/body12a
• Rectus+abdominis+muscle at eMedicine Dictionary
• Roche Lexicon - illustrated navigator, at Elsevier 25466.180-1