| 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 the lumbar spine |
| Antagonist |
Erector spinae |
The rectus abdominis muscle, also known as the "six pack" or "washboard abs"[1], 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 and pubic tubercle inferiorly to the xiphoid process and costal cartilages of ribs V to VII superiorly.[2]
It is contained in the rectus sheath, consisting of the aponeuroses of the lateral abdominal muscles.
The rectus is crossed by three (rarely four) fibrous bands called the tendinous intersections. This causes the formation of six muscle bellies, giving rise to its common name as the "six-pack."
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Contents
- 1 Function
- 2 Blood supply
- 3 Innervation
- 4 Location
- 5 Damage
- 6 Animals
- 7 Additional images
- 8 See also
- 9 References
- 10 External links
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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[3] 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.
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
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This section does not cite any references or sources. (October 2009) |
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
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This section requires expansion with: Animal examples needed. (January 2009) |
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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See also
- Divarication of rectus abdominis muscles
References
- ^ Tankini#Usage
- ^ Gray's Anatomy for students, 2nd edition, Page:176
- ^ Mathes SJ, Nahai F. Classification of the vascular anatomy of muscles: experimental and clinical correlation. Plast Reconstr Surg. Feb 1981;67(2):177-87.
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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List of muscles of abdominopelvic cavity (TA A04.5, GA 4.408)
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Abdomen/
wall |
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Anterior/
lateral
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Muscle
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Abdominal external oblique · Transversus abdominis/Conjoint tendon · Rectus sheath (rectus abdominis, pyramidalis) · Arcuate line · Tendinous intersection
Cremaster · Abdominal internal oblique
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Fascia
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Fascia/abdominal fascia: panniculus adiposus (Fascia of Camper) · stratum membranosum (Fascia of Scarpa) · Transversalis fascia (Interfoveolar ligament)
Linea alba · Linea semilunaris · Inguinal triangle
Inguinal canal (Deep inguinal ring, Superficial inguinal ring, Intercrural fibers, Crura of superficial inguinal ring)
Inguinal ligament (Pectineal ligament, Lacunar ligament, Reflected ligament)
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Posterior
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Muscle
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quadratus lumborum · psoas major/psoas minor · iliacus
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Fascia
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iliopsoas fascia (Iliac fascia/Iliopectineal arch)
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| Pelvis |
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Muscle
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levator ani (iliococcygeus, pubococcygeus, puborectalis) · coccygeus
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Fascia
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fascia/pelvic fascia visceral (Rectovaginal fascia, Rectoprostatic fascia) · parietal (Obturator fascia/Tendinous arch, Piriformis fascia)
floor/diaphragm: Superior fascia of pelvic diaphragm (Pubovesical ligament, Puboprostatic ligament) · Inferior fascia of pelvic diaphragm
Anococcygeal body
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anat (h/n, u, t/d, a/p, l)/phys/devp/hist
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noco(m, s, c)/cong(d)/tumr, sysi/epon, injr
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