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Rectus abdominis muscle: want to learn more about it?

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Rectus abdominis muscle

Rectus abdominis muscle (Musculus rectus abdominis)

Rectus abdominis, informally known as the abs muscle, is a long muscle of the anterior abdominal wall. In those with low body fat, it is clearly visible beneath the skin forming the ‘six pack’. It extends from the rib cage all the way to the pubic bone. 

Rectus abdominis belongs to the anterior abdominal muscles together with pyramidalis muscle. But taking the functional anatomy into account, these two muscles comprise the anterolateral abdominal wall along with the three lateral abdominal muscles; external oblique, internal oblique and transversus abdominis.

Key facts about the rectus abdominis muscle
Origin Pubic symphysis, pubic crest
Insertion Xiphoid process, costal cartilages of ribs 5-7
Innervation Intercostal nerves (T7-T11), subcostal nerve (T12)
Blood supply Inferior epigastric and superior epigastric arteries; contributions from posterior intercostal, subcostal and deep circumflex arteries
Function Trunk flexion, compresses abdominal viscera, expiration

This article will discuss the anatomy and function of the rectus abdominis muscle.

Origin and insertion

Inferiorly the rectus abdominis muscle is attached by two tendons; the larger one is attached to the pubic crest, from the pubic tubercle to the pectineal line, while the small, medial tendon is attached to the pubic symphysis.

The fibres of the rectus abdominis then extend vertically superiorly and insert into the xiphoid process of sternum and costal cartilages of the 5th, 6th and 7th ribs. Generally speaking, the most lateral fibres attach to the anterior end of the 5th rib, however in some cases it extends to the 3rd and 4th ribs, or this slip is absent altogether.

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Structure 

The rectus abdominis muscle is paired muscle that runs vertically, either side of the linea alba, on the anterior surface of the abdominal wall. The linea alba is a band of connective tissue that divides the two halves of the muscle vertically.

The linea semilunaris is the tendinous intersection that separates the lateral edge of the muscle from the external oblique and internal oblique muscles that lie on the lateral surface of the anterior abdominal wall. It usually extends from tip of the ninth costal cartilage to the pubic tubercle.

Anterior abdominal wall in a cadaver, showing the rectus abdominis muscle. Notice the linea alba extending across the mid-line.

Finally, there are three tendinous intersections in the rectus abdominis muscle. One of these horizontal intersections is present at the level of umbilicus, another at the level of xiphoid process and the third mid way between them. These fibrous bands divide the muscle into segments, resulting in a grid iron ‘six pack’ shape in those with low body fat. The intersections are believed to be representations of myosepta which delineate the muscle forming myotomes.

Learn the anatomy of the abdominal muscles with our articles, video tutorials, quizzes, and labeled diagrams.

Relations

The rectus abdominis muscle itself lies within the rectus sheath, which is formed by the merging of the aponeurosis of transversus abdominis, external and internal oblique abdominal muscles.

Innervation

The rectus abdominis muscle is innervated by the thoracoabdominal nerves, which enter the rectus sheath by piercing its anterior surface.

They pass between the transversus abdominis and internal oblique muscle layers, and pierce the sheath of the rectus abdominis muscle.

The nerves are simply the anterior divisions of the 7th to 11th lower intercostal nerves, that continue to supply the abdominal wall after the intercostal spaces they supplied end medially.

Blood supply

The blood supply to the rectus abdominis muscle arises from a number of vessels, but predominantly the inferior and superior epigastric arteries

In addition, small terminal branches of the lower three posterior intercostal arteries, subcostal and deep circumflex artery also provide some contribution.

Functions

Rectus abdominis  flexes the trunk anteriorly. Moreover, working together with other abdominal muscles, this muscle compresses the abdominal viscera and increases the intra-abdominal pressure, which has an important function in processes such as forced breathing, labor, defecation and micturition.

The rectus abdominis also stabilizes and controls tilt of the pelvis (antilordosis). 

Consolidate your knowledge about the muscles of the abdominal wall with our quiz.

Rectus abdominis muscle: want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

What do you prefer to learn with?

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

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