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ABDOMINAL MUSCLES ABDOMINAL WALL 24. 04. 2014 Kaan Yücel M.D., Ph.D. http://yeditepeanatomy1.org Dr. Kaan Yücel http://yeditepeanatomy1.org Abdominal muscles & Abdominal wall Although the abdominal wall is continuous, it is subdivided into the anterior wall, right and left lateral walls, and posterior wall for descriptive purposes. The wall is musculoaponeurotic, except for the posterior wall, which includes the lumbar region of the vertebral column. The boundary between the anterior and the lateral walls is indefinite, therefore the term anterolateral abdominal wall is often used. The anterolateral abdominal wall is bounded superiorly by the cartilages of the 7th-10th ribs and the xiphoid process of the sternum, and inferiorly by the inguinal ligament and the superior margins of the anterolateral aspects of the pelvic girdle (iliac crests, pubic crests, and pubic symphysis). The superficial fascia of the abdominal wall (subcutaneous tissue of abdomen) is a layer of fatty connective tissue and continuous with, the superficial fascia throughout other regions of the body. Below the umbilicus, it forms two layers: a superficial fatty layer and a deeper membranous layer. The superficial fatty layer of superficial fascia (Camper's fascia) contains fat and varies in thickness. The deeper membranous layer of superficial fascia (Scarpa's fascia) is thin and membranous, and contains little or no fat. Inferiorly, it continues into the thigh, but just below the inguinal ligament, it fuses with the deep fascia of the thigh (the fascia lata). There are five muscles in the anterolateral group of abdominal wall muscles: three flat muscles whose fibers begin posterolaterally, pass anteriorly, and are replaced by an aponeurosis as the muscle continues towards the midline: external oblique, internal oblique, and transversus abdominis muscles; two vertical muscles, near the midline, which are enclosed within a tendinous sheath formed by the aponeuroses of the flat muscles-the rectus abdominis and pyramidalis muscles. The most superficial of the three flat muscles in the anterolateral group of abdominal wall muscles is the external oblique, which is immediately deep to the superficial fascia. Deep to the external oblique muscle is the internal oblique muscle, which is the second of the three flat muscles. Deep to the internal oblique muscle is the transversus abdominis muscle, so named because of the direction of most of its muscle fibers. Functions of the muscles of the anterolateral abdominal wall: -Form a strong expandable support for the anterolateral abdominal wall. -Support the abdominal viscera and protect them from most injuries. -Compress the abdominal contents to maintain or increase the intra-abdominal pressure and, in so doing, oppose the diaphragm (increased intra-abdominal pressure facilitates expulsion). -Move the trunk and help to maintain posture. External oblique is innervated by T7-T11 spinal nerves and subcostal nerve. Internal oblique is innervated by the anterior rami of T6-T12 spinal nerves) and first lumbar nerves.Transversus abdominis is innervated by the anterior rami of T6-T12 spinal nerves) and first lumbar nerves.Rectus abdominis is innervated by the anterior rami of T6T12 spinal nerves. The main paired muscles in the posterior abdominal wall are the: Psoas major: passing inferolaterally. Iliacus: lying along the lateral sides of the inferior part of the psoas major. Quadratus lumborum: lying adjacent to the transverse processes of the lumbar vertebrae and lateral to superior parts of the psoas major. The psoas passes inferolaterally, deep to the inguinal ligament to reach the lesser trochanter of the femur. The lumbar plexus of nerves is embedded in the posterior part of the psoas, anterior to the lumbar transverse processes. The psoas major muscle flexes the thigh at the hip joint when the trunk is stabilized and flexes the trunk against gravity when the body is supine. It is innervated by anterior rami of nerves L1 to L3. Associated with the psoas major muscle is the psoas minor muscle, which is sometimes absent.It lies on the surface of the psoas major when present. It is a weak flexor of the lumbar vertebral column and is innervated by the anterior ramus of nerve L1. Laterally, the quadratus lumborum muscles fill the space between ribs XII and the iliac crest on both sides of the vertebral column. They are overlapped medially by the psoas major muscles. The quadratus lumborum muscles depress and stabilize the twelfth ribs and contribute to lateral bending of the trunk. They are innervated by anterior rami of T12 and L1 to L4 spinal nerves. Inferiorly, an iliacus muscle fills the iliac fossa on each side. It joins with the psoas major muscle, and attaches to the lesser trochanter of the femur. As they pass into the thigh, these combined muscles are referred to as the iliopsoas muscle.Together the psoas and iliacus form the iliopsoas, the chief flexor of the thigh. It is also a stabilizer 2 of the hip joint and helps maintain the erect posture at this joint. The psoas and iliacus share in hip flexion; however, only the psoas can produce movement (flexion or lateral bending) of the lumbar vertebral column. It is innervated by branches of the femoral nerve. Dr. Kaan Yücel http://yeditepeanatomy1.org Abdominal muscles & Abdominal wall 1. ABDOMINAL WALL The abdomen is the part of the trunk between the thorax and the pelvis. It is a flexible, dynamic container, housing most of the organs of the alimentary system and part of the urogenital system. Containment of the abdominal organs and their contents is provided by musculoaponeurotic walls anterolaterally, the diaphragm superiorly, and the muscles of the pelvis inferiorly. The anterolateral musculoaponeurotic walls are suspended between and supported by two bony rings (the inferior margin of the thoracic skeleton superiorly and pelvic girdle inferiorly) linked by a semirigid lumbar vertebral column in the posterior abdominal wall. Interposed between the more rigid thorax and pelvis, this arrangement enables the abdomen to enclose and protect its contents while providing the flexibility required by respiration, posture, and locomotion. Through voluntary or reflexive contraction, its muscular roof, anterolateral walls, and floor can raise internal (intraabdominal) pressure to aid expulsion from the abdominopelvic cavity or from the adjacent thoracic cavity, expulsion of air from the thoracic cavity (lungs and bronchi) or of fluid (e.g., urine or vomitus), flatus, feces, or fetuses from the abdominopelvic cavity. The abdominal wall covers a large area. It is bounded superiorly by the xiphoid process and costal margins, posteriorly by the vertebral column, and inferiorly by the upper parts of the pelvic bones. Its layers consist of skin, superficial fascia (subcutaneous tissue), muscles and their associated deep fascias, extraperitoneal fascia, and parietal peritoneum. Although the abdominal wall is continuous, it is subdivided into the anterior wall, right and left lateral walls, and posterior wall for descriptive purposes. The wall is musculoaponeurotic, except for the posterior wall, which includes the lumbar region of the vertebral column. The boundary between the anterior and the lateral walls is indefinite, therefore the term anterolateral abdominal wall is often used. Some structures, such as muscles and cutaneous nerves, are in both the anterior and lateral walls. The anterolateral abdominal wall extends from the thoracic cage to the pelvis. The anterolateral abdominal wall is bounded superiorly by the cartilages of the 7th-10th ribs and the xiphoid process of the sternum, and inferiorly by the inguinal ligament and the superior margins of the anterolateral aspects of the pelvic girdle (iliac crests, pubic crests, and pubic symphysis). Superficial fascia The superficial fascia of the abdominal wall (subcutaneous tissue of abdomen) is a layer of fatty connective tissue. It is usually a single layer similar to, and continuous with, the superficial fascia throughout other regions of the body. However, in the lower region of the anterior part of the abdominal wall, below the umbilicus, it forms two layers: a superficial fatty layer and a deeper membranous layer. 3 Dr. Kaan Yücel http://yeditepeanatomy1.org Abdominal muscles & Abdominal wall Superficial layer The superficial fatty layer of superficial fascia (Camper's fascia) contains fat and varies in thickness. It is continuous over the inguinal ligament with the superficial fascia of the thigh and with a similar layer in the perineum. In men, this superficial layer continues over the penis and, after losing its fat and fusing with the deeper layer of superficial fascia, continues into the scrotum where it forms a specialized fascial layer containing smooth muscle fibers (the dartos fascia). In women, this superficial layer retains some fat and is a component of the labia majora. The deeper membranous layer of superficial fascia (Scarpa's fascia) is thin and membranous, and contains little or no fat. Inferiorly, it continues into the thigh, but just below the inguinal ligament, it fuses with the deep fascia of the thigh (the fascia lata). In the midline, it is firmly attached to the linea alba and the symphysis pubis. It continues into the anterior part of the perineum where it is firmly attached to the ischiopubic rami and to the posterior margin of the perineal membrane. Here, it is referred to as the superficial perineal fascia (Colles' fascia). The deep fascia of the abdominal wall is continous with the fascia lata inferiorly in the thigh, and is also continous with the fascia of the perineum posteriorly and the deep fascia covering the adductor muscles of the thigh laterally. There are five muscles in the anterolateral group of abdominal wall muscles: three flat muscles whose fibers begin posterolaterally, pass anteriorly, and are replaced by an aponeurosis as the muscle continues towards the midline: external oblique, internal oblique, and transversus abdominis muscles; two vertical muscles, near the midline, which are enclosed within a tendinous sheath formed by the aponeuroses of the flat muscles-the rectus abdominis and pyramidalis muscles. Each of these five muscles has specific actions, but together the muscles are critical for the maintenance of many normal physiological functions. By their positioning, they form a firm, but flexible, wall that keeps the abdominal viscera within the abdominal cavity, protects the viscera from injury, and helps maintain the position of the viscera in the erect posture against the action of gravity. In addition, contraction of these muscles assists in both quiet and forced expiration by pushing the viscera upward (which helps push the relaxed diaphragm further into the thoracic cavity) and in coughing and vomiting. All these muscles are also involved in any action that increases intra-abdominal pressure, including parturition (childbirth), micturition (urination), and defecation (expulsion of feces from the rectum). 4 Dr. Kaan Yücel http://yeditepeanatomy1.org Abdominal muscles & Abdominal wall Flat muscles The most superficial of the three flat muscles in the anterolateral group of abdominal wall muscles is the external oblique, which is immediately deep to the superficial fascia. Its laterally placed muscle fibers pass in an inferomedial direction, while its large aponeurotic component covers the anterior part of the abdominal wall to the midline. Approaching the midline, the aponeuroses are entwined, forming the linea alba, which extends from the xiphoid process to the pubic symphysis. Associated ligaments The lower border of the external oblique aponeurosis forms the inguinal ligament (Poupart’s ligament) on each side. This thickened reinforced free edge of the external oblique aponeurosis passes between the anterior superior iliac spine laterally and the pubic tubercle medially. It folds under itself forming a trough, which plays an important role in the formation of the inguinal canal. Several other ligaments are also formed from extensions of the fibers at the medial end of the inguinal ligament: lacunar ligament is a crescent-shaped extension of fibers at the medial end of the inguinal ligament that pass backward to attach to the pecten pubis on the superior ramus of the pubic bone; additional fibers extend from the lacunar ligament along the pecten pubis of the pelvic brim to form the pectineal (Cooper's) ligament. Deep to the external oblique muscle is the internal oblique muscle, which is the second of the three flat muscles. This muscle is smaller and thinner than the external oblique, with most of its muscle fibers passing in a superomedial direction. Its lateral muscular components end anteriorly as an aponeurosis that blends into the linea alba at the midline. Deep to the internal oblique muscle is the transversus abdominis muscle, so named because of the direction of most of its muscle fibers. It ends in an anterior aponeurosis, which blends with the linea alba at the midline. Transversalis fascia Each of the three flat muscles is covered on its anterior and posterior surfaces by a layer of deep fascia. In general, these layers are unremarkable except for the layer deep to the transversus abdominis muscle (the transversalis fascia), which is better developed. The transversalis fascia is a continuous layer of deep fascia that 5 Dr. Kaan Yücel http://yeditepeanatomy1.org Abdominal muscles & Abdominal wall lines the abdominal cavity and continues into the pelvic cavity. It crosses the midline anteriorly, associating with the transversalis fascia of the opposite side, and is continuous with the fascia on the inferior surface of the diaphragm. It is continuous posteriorly with the deep fascia covering the muscles of the posterior abdominal wall and attaches to the thoracolumbar fascia. There is therefore a continuous layer of deep fascia surrounding the abdominal cavity that is thick in some areas, thin in others, attached or free, and participates in the formation of specialized structures. Vertical muscles The two vertical muscles in the anterolateral group of abdominal wall muscles are the large rectus abdominis and the small pyramidalis. The rectus abdominis is a long, flat muscle and extends the length of the anterior abdominal wall. It is a paired muscle, separated in the midline by the linea alba, and it widens and thins as it ascends from the pubic symphysis to the costal margin. Along its course, it is intersected by three or four transverse fibrous bands or tendinous intersections. These are easily visible on individuals with a well-developed rectus abdominis (Kaan’s note: “Not me”). The second vertical muscle is the pyramidalis. This small, triangular muscle, which may be absent, is anterior to the rectus abdominis, has its base on the pubis, and its apex is attached superiorly and medially to the linea alba. It is innervated by the anterior ramus of T12 (twelth thoracic spinal nerve) . The rectus sheath is separated from its fellow on the opposite side by a fibrous band called the linea alba. This extends from the xiphoid process down to the symphysis pubis and is formed by the fusion of the aponeuroses of the lateral muscles of the two sides. Wider above the umbilicus, it narrows down below the umbilicus to be attached to the symphysis pubis. The posterior wall of the rectus sheath is not attached to the rectus abdominis muscle. The anterior wall is firmly attached to it by the muscle's tendinous intersections. Rectus sheath The rectus abdominis and pyramidalis muscles are enclosed in an aponeurotic tendinous sheath (rectus sheath) formed by a unique layering of the aponeuroses of the external and internal oblique, and transversus abdominis muscles. The rectus sheath completely encloses the upper three-quarters of the rectus abdominis and covers the anterior surface of the lower one-quarter of the muscle. At a point midway between the 6 Dr. Kaan Yücel http://yeditepeanatomy1.org Abdominal muscles & Abdominal wall umbilicus and the pubic symphysis, corresponding to the beginning of the lower one-quarter of the rectus abdominis muscle, all of the aponeuroses move anterior to the rectus muscle. There is no posterior wall of the rectus sheath and the anterior wall of the sheath consists of the aponeuroses of the external oblique, the internal oblique, and the transversus abdominis muscles. As no sheath covers the posterior surface of the lower quarter of the rectus abdominis muscle, the muscle at this point is in direct contact with the transversalis fascia. Marking this point of transition is an arch of fibers (the arcuate line). The formation of the rectus sheath surrounding the upper three-quarters of the rectus abdominis muscle has the following pattern: anterior wall consists of the aponeurosis of the external oblique and half of the aponeurosis of the internal oblique, which splits at the lateral margin of the rectus abdominis; posterior wall of the rectus sheath consists of the other half of the aponeurosis of the internal oblique and the aponeurosis of the transversus abdominis. FUNCTIONS AND ACTIONS OF ANTEROLATERAL ABDOMINAL MUSCLES The muscles of the anterolateral abdominal wall: Form a strong expandable support for the anterolateral abdominal wall. Support the abdominal viscera and protect them from most injuries. Compress the abdominal contents to maintain or increase the intra-abdominal pressure and, in so doing, oppose the diaphragm (increased intra-abdominal pressure facilitates expulsion). Move the trunk and help to maintain posture. The oblique and transverse muscles, acting together bilaterally, form a muscular girdle that exerts firm pressure on the abdominal viscera. The rectus abdominis participates little, if at all, in this action. Compressing the abdominal viscera and increasing intra-abdominal pressure elevates the relaxed diaphragm to expel air during respiration and more forcibly for coughing, sneezing, nose blowing, voluntary eructation (burping), and yelling or screaming. When the diaphragm contracts during inspiration, the anterolateral abdominal wall expands as its muscles relax to make room for the organs, such as the liver, that are pushed inferiorly. The combined actions of the anterolateral muscles also produce the force required for defecation (discharge of feces), micturition (urination), vomiting, and parturition (childbirth). Increased intra-abdominal (and intrathoracic) pressure is also involved in heavy lifting, the resulting force sometimes producing a hernia. The anterolateral abdominal muscles are also involved in movements of the trunk at the lumbar vertebrae and in controlling the tilt of the pelvis when standing for maintenance of posture (resisting lumbar lordosis). Consequently, strengthening the anterolateral abdominal wall musculature improves standing and sitting posture. The rectus abdominis is a powerful flexor of the thoracic and especially lumbar regions of the vertebral column, pulling the anterior costal margin and pubic crest toward each other. The oblique abdominal muscles 7 Dr. Kaan Yücel http://yeditepeanatomy1.org Abdominal muscles & Abdominal wall also assist in movements of the trunk, especially lateral flexion and rotation of the lumbar and lower thoracic vertebral column. The transversus abdominis probably has no appreciable effect on the vertebral column. The main paired muscles in the posterior abdominal wall are the: Psoas major: passing inferolaterally. Iliacus: lying along the lateral sides of the inferior part of the psoas major. Quadratus lumborum: lying adjacent to the transverse processes of the lumbar vertebrae and lateral to superior parts of the psoas major. Muscles forming the medial, lateral, inferior, and superior boundaries of the posterior abdominal region fill in the bony framework of the posterior abdominal wall. The long, thick, fusiform psoas major lies lateral to the lumbar vertebrae. Psoas is a Greek word meaning “muscle of the loin.” (Butchers refer to the psoas of animals as the tenderloin.) The psoas major passes inferolaterally, deep to the inguinal ligament to reach the lesser trochanter of the femur. The lumbar plexus of nerves is embedded in the posterior part of the psoas, anterior to the lumbar transverse processes. Medially, the psoas major muscles cover the anterolateral surface of the bodies of the lumbar vertebrae, filling in the space between the vertebral bodies and the transverse processes. Passing inferiorly along the pelvic brim, each muscle continues into the anterior thigh, under the inguinal ligament, to attach to the lesser trochanter of the femur. The psoas major muscle flexes the thigh at the hip joint when the trunk is stabilized and flexes the trunk against gravity when the body is supine. It is innervated by anterior rami of nerves L1 to L3. Associated with the psoas major muscle is the psoas minor muscle, which is sometimes absent. Lying on the surface of the psoas major when present, this slender muscle arises from vertebrae TXII and LI and the intervening intervertebral disc; its long tendon inserts into the pectineal line of the pelvic brim and the iliopubic eminence. The psoas minor is a weak flexor of the lumbar vertebral column and is innervated by the anterior ramus of nerve L1. 8 Dr. Kaan Yücel http://yeditepeanatomy1.org Abdominal muscles & Abdominal wall Laterally, the quadratus lumborum muscles fill the space between ribs XII and the iliac crest on both sides of the vertebral column. They are overlapped medially by the psoas major muscles; along their lateral borders are the transversus abdominis muscles. The quadrilateral quadratus lumborum forms a thick muscular sheet in the posterior abdominal wall. It lies adjacent to the lumbar transverse processes and is broader inferiorly. Branches of the lumbar plexus run inferiorly on the anterior surface of this muscle. Each quadratus lumborum muscle arises from the transverse processes of L5, the iliolumbar ligament, and the adjoining part of the iliac crest. The muscle attaches superiorly to the transverse process of the first four lumbar vertebrae and the inferior border of rib XII. The quadratus lumborum muscles depress and stabilize the twelfth ribs and contribute to lateral bending of the trunk. Acting together, the muscles may extend the lumbar part of the vertebral column. They are innervated by anterior rami of T12 and L1 to L4 spinal nerves. Inferiorly, an iliacus muscle fills the iliac fossa on each side. From this expansive origin covering the iliac fossa, the muscle passes inferiorly, joins with the psoas major muscle, and attaches to the lesser trochanter of the femur. As they pass into the thigh, these combined muscles are referred to as the iliopsoas muscle. The iliacus is a large triangular muscle that lies along the lateral side of the inferior part of the psoas major. Most of its fibers join the tendon of the psoas major. Together the psoas and iliacus form the iliopsoas, the chief flexor of the thigh. It is also a stabilizer of the hip joint and helps maintain the erect posture at this joint. The psoas and iliacus share in hip flexion; however, only the psoas can produce movement (flexion or lateral bending) of the lumbar vertebral column. It is innervated by branches of the femoral nerve. 9 Dr. Kaan Yücel http://yeditepeanatomy1.org Abdominal muscles & Abdominal wall Table 1 . Muscles of the anterolateral abdominal wall Muscle External oblique Origin Insertion Innervation Main Actiona External surfaces of 5th- Linea alba, pubic T7-T11 spinal Compresses and 12th ribs tubercle, and anterior nerves and supports abdominal half of iliac crest subcostal nerve viscera,b flexes and rotates trunk Internal oblique Thoracolumbar fascia, Inferior borders of 10th- Anterior rami of Compresses and anterior 2/3 of iliac 12th ribs, linea alba, and T6-T12 spinal supports abdominal crest, and connective pecten pubis via conjoint nerves) and first viscera, flexes and tissue deep to lateral 1/3 tendon lumbar nerves rotates trunk of inguinal ligament Transversus Internal surfaces of 7th- Linea alba with Anterior rami of Compresses and abdominis 12th costal cartilages, aponeurosis of internal T6-T12 spinal supports abdominal thoracolumbar fascia, oblique, pubic crest, and nerves) and first viscerab iliac crest, and pecten pubis via conjoint lumbar nerves connective tissue deep tendon to lateral 1/3 of inguinal ligament Rectus abdominis Pubic symphysis and pubic crest Xiphoid process and 5th- Anterior rami of Compress abdominal 7th costal cartilages T6-T12 spinal contents; flex nerves vertebral column; tense abdominal wall Pyramidalis * Front of pubis and pubic symphysis Into linea alba Anterior ramus of Tenses the linea alba T12 * Approximately 80% of people have an insignificant muscle, the pyramidalis,which is located in the rectus sheath anterior to the most inferior part of the rectus abdominis. It extends from the pubic crest of the hip bone to the linea alba. This small muscle draws down on the linea alba. 10 Dr. Kaan Yücel http://yeditepeanatomy1.org Abdominal muscles & Abdominal wall Table 2 . Muscles of the posterior abdominal wall Muscle Origin Insertion Innervation Main Action Psoas major Transverse processes of By a strong tendon Anterior rami of lumbar Acting inferiorly with lumbar vertebrae; to lesser nerves L1, L2, L3 iliacus, it flexes thigh; bodies of T12-L5 trochanter of acting superiorly it vertebrae and femur flexes vertebral intervening column laterally; it is intervertebral discs used to balance the trunk; when sitting it acts inferiorly with iliacus to flex trunk Psoas minor TXII and LI vertebrae Pectineal line of Anterior rami of L1 Weak flexion of the pelvic brim lumbar vertebral and iliopubic column eminence Iliacus Superior 2/3 of iliac Lesser trochanter Femoral nerve Flexes thigh and fossa, ala of sacrum, and of femur and shaft stabilizes hip joint; anterior sacroiliac inferior to it, and acts with psoas major ligaments to psoas major tendon Quadratus Transverse process of L5, Transverse process Anterior branches of T12 Depress and stabilize lumborum Iliolumbar ligament, iliac of the first four rib XII during crest lumbar vertebrae inspiration and some and the inferior lateral flexion of border of rib XII. trunk and L1-L4 nerves 11