The
rectus abdominis muscle is a paired
muscleMuscle is the contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
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 symphysisThe pubic symphysis is the midline cartilaginous joint uniting the superior rami of the left and right pubic bones. It is located anterior to the urinary bladder and superior to the external genitalia; for females it is above the vulva and for males it is above the penis. In males, the suspensory...
/pubic crest inferiorly to the xiphisternum/xiphoid process and lower costal cartilages (5–7) superiorly.
It is contained in the
Rectus sheathThe Rectus sheath is formed by the aponeuroses of the Obliqui and Transversus. It contains the Rectus abdominis and Pyramidalis muscles.It can be divided into anterior and posterior laminae....
.
The rectus is usually crossed by three fibrous bands linked by the tendinous inscriptions.
The
rectus abdominis muscle is a paired
muscleMuscle is the contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
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 symphysisThe pubic symphysis is the midline cartilaginous joint uniting the superior rami of the left and right pubic bones. It is located anterior to the urinary bladder and superior to the external genitalia; for females it is above the vulva and for males it is above the penis. In males, the suspensory...
/pubic crest inferiorly to the xiphisternum/xiphoid process and lower costal cartilages (5–7) superiorly.
It is contained in the
Rectus sheathThe Rectus sheath is formed by the aponeuroses of the Obliqui and Transversus. It contains the Rectus abdominis and Pyramidalis muscles.It can be divided into anterior and posterior laminae....
.
The rectus is usually crossed by three fibrous bands linked 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 ("eightpack"), ten, or—even rarer—asymmetrically arranged segments. All these variations are functionally equivalent.
Function
The rectus abdominis is a key
posturalPosture or posturing may refer to:In humans* Neutral spine or good posture* Human position* Abnormal posturing, in neurotrauma* Posturography, in neurology* Posture and Occupational HealthIn biology...
muscle. It is responsible for flexing the lumbar spine, as when doing a "
crunchThe crunch, also known as curl-up, is one of the most common exercises for the abdominal muscles, primarily the rectus abdominis. It is considered a safer alternative to the sit-up.-Form:...
". The rectus abdominis assists with breathing and plays an important role in
respirationIn animal physiology, respiration is the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
in the event the patient is
short of breathDyspnea or dyspnoea , from Latin dyspnoea, from Greek dyspnoia from dyspnoos, shortness of breath) or shortness of breath is a debilitating symptom that is the experience of unpleasant or uncomfortable respiratory sensations...
. 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.
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 2 dominant pedicles. First, the
inferior epigastric arteryIn human anatomy, inferior epigastric artery refers to the artery that arises from the external iliac artery and anastomoses with the superior epigastric artery...
and vein (or veins) run superiorly on the posterior surface of the rectus abdominis, enter the rectus fascia at the
arcuate lineThe arcuate line of the abdomen is a horizontal line that demarcates the lower limit of the posterior layer of the rectus sheath. It is also where the inferior epigastric vessels perforates the rectus abdominus....
, and serve the lower part of the muscle. Second, the
superior epigastric arteryIn human anatomy, superior epigastric artery refers to a blood vessel that carries oxygenated blood and arises from the internal thoracic artery...
, a terminal branch of the
internal thoracic arteryIn human anatomy, the internal thoracic artery , previously known as the internal mammary artery , is an artery that supplies the anterior chest wall and the breasts...
, supplies blood to the upper portion. Finally, numerous small segmental contributions come from the lower 6 intercostal arteries as well.
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 ligamentsThe Costoxiphoid Ligaments connect the anterior and posterior surfaces of the seventh costal cartilage, and sometimes those of the sixth, to the front and back of the xiphoid process....
, and the side of the
xiphoid processThe xiphoid process, also known as the xiphisternum, is a small cartilaginous extension to the lower part of the sternum which is usually ossified in the adult human. By age 15 to 29, the xiphoid usually fuses to the body of the sternum with a fibrous joint. Unlike the synovial articulation of...
.
Animals
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.
External links
– "Muscles of the anterior chest wall with the pectoralis major muscles removed." – "Thoracic Wall: The Anterior Thoracic Wall" – "Incision and reflection of the external abdominal oblique muscle." – "Incision and reflection of the internal abdominal oblique muscle." – "Anterior Abdominal Wall: The Rectus Abdominis Muscle"