Rectus abdominis muscle
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| Rectus abdominis | |
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| 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 trunk/lumbar vertebrae |
| Antagonist | Erector spinae |
The rectus abdominis muscle is a paired muscle running vertically on each side of the anterior wall of the human abdomen (and in some other animals). 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 inferiorly to the xiphisternum/xiphoid process and lower costal cartilages (5-7) superiorly.
It is contained in the Rectus sheath.
The rectus is usually crossed by three fibrous bands licked by the tendinous inscriptions. While the "sixpack" is by far the most common configuration of the muscle bellies of the rectus, there exist rare anatomic variations which result in the appearance of eight (four per side) muscle segments ("eightpack"), or, even rarer, ten asymmetrically arranged segments. All these variations are functionally equivalent.
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[edit] Colloquial Names
Colloquial names for the appearance of a well-defined rectus abdominis include a "six pack", "washboard abs", "abs of steel", "rock hard abs" and often carry cultural connotations of superior physical fitness.
[edit] Function
The rectus abdominis is a key postural muscle. It is responsible for flexing the lumbar spine, as when doing a 'crunch'. The rectus abdominis assists with breathing and plays an important role in respiration in the event the patient is short of breath. 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.
[edit] Blood supply
The rectus abdominis has several sources of arterial blood supply. In reconstructive surgery terms, it is a Mathes and Nahai[1] Type III muscle with 2 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 6 intercostal arteries as well.
[edit] 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.
[edit] Animals
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This section requires expansion with: Animal examples needed. |
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.
[edit] Additional images
 Anterior surface of sternum and costal cartilages. |
 The interfoveolar ligament, seen from in front. |
 Diagram of sheath of Rectus. |
 Diagram of a transverse section through the anterior abdomina wall, below the linea semicircularis. |
 The relations of the femoral and abdominal inguinal rings, seen from within the abdomen. Right side. |
 Horizontal disposition of the peritoneum in the lower part of the abdomen. |
 Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas. |
 The left side of the thorax. |
 Surface anatomy of the front of the thorax and abdomen. |
 Muscles of the trunk |
[edit] References
- ^ Mathes SJ, Nahai F. Classification of the vascular anatomy of muscles: experimental and clinical correlation. Plast Reconstr Surg. Feb 1981;67(2):177-87.
[edit] 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
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