BMS100_Abdominal Wall Muscles.docx

BMS100 – MSK5 ANTERIOR AND POSTERIOR ABDOMINAL WALL MUSCLES AND INGUINAL CANAL ANTERIOR AND LATERAL ABDOMINAL WALL MUSCLES MUSCLE ATTACHMENT/LOCATION INNERVATION MAIN ACTION/ROLE Obliquus externus abdominis Situated on lateral and anterior parts of the abdomen; largest and most superficial...

BMS100 – MSK5 ANTERIOR AND POSTERIOR ABDOMINAL WALL MUSCLES AND INGUINAL CANAL ANTERIOR AND LATERAL ABDOMINAL WALL MUSCLES MUSCLE ATTACHMENT/LOCATION INNERVATION MAIN ACTION/ROLE Obliquus externus abdominis Situated on lateral and anterior parts of the abdomen; largest and most superficial of three muscles in this region Origin: external surfaces of lower 8 ribs Insertion: linea alba, pubic tubercle, anterior half of iliac crest Intercostal nerves (T7 to T12) Flex the trunk (bilateral) Contralateral rotation of trunk Compress the abdominal contents Obliquus internus abdominis Situated on lateral and anterior parts of abdomen; thinner and smaller than externus – irregular quadrilateral form Origin: lateral 1/3 of inguinal ligament, anterior 2/3 of iliac crest, thoracolumbar fascia Insertion: linea alba, lower 3 ribs Intercostal nerves T6 to T12 and L1 Ipsilateral rotation (unilateral) Flexion of the trunk (bilateral) Compress the abdominal contents Transversus abdominus muscle Most internal of the flat muscles of the abdomen Origin: inguinal ligament, iliac crest, thoracolumbar fascia, cartilages of the lower 6 ribs Insertion: linea alba Intercostal nerves T6 to T12 and L1 Compress abdominal contents Rectus abdominis Long flat muscle extending the whole length of abdomen and separated from its opposite side by linea alba Crossed by three fibrous bands called tendinous intersections Origin: pubic crest and symphysis pubis Insertion: xiphoid process, cartilages of ribs 5, 6, 7 Intercostal nerves T6 to T12 Flexion of trunk at the spinal joints Posterior tilt of pelvis Compress the abdominal contents Layers of the Abdominal Wall Skin Camper’s fascia – fatty layer Camper’s fascia: thick superficial layer of adipose and areolar connective tissue sitting just deep to skin More prominent in lower aspect of abdomen; inferior to umbilicus Scarpa’s fascia – deep membranous layer Scarpa’s fascia: sits between Camper’s fascia and rectus sheath; anchored laterally to aponeurosis of the external oblique and medially to the linea alba of rectus sheath Rectus sheath – protective covering over rectus abdominus Rectus sheath: composed of aponeurosis of the three flat muscles (external and internal oblique, transversus abdominus) as they converge in the midline to form the median linea alba; durable, resilient and fibrous compartment that contains and protects the rectus abdominus Composition of sheath changes inferior to the umbilicus and arrangement of muscle layers changes depending on location with respect to the arcuate line Arcuate line: located ½ of the distance between umbilicus and pubic symphysis Inferior to this line – all three abdominal muscles pass anterior to the rectus abdominis muscle Rectus sheath superior to arcuate line: Anterior lamina (sheet) – full aponeurosis of external oblique and anterior ½ of the aponeurosis of the internal oblique Posterior lamina (sheet) – posterior ½ of the aponeurosis of the internal oblique and full aponeurosis of transversus abdominis Rectus sheath inferior to arcuate line: Anterior lamina (sheet) – aponeuroses of all three abdominal muscles Posterior lamina (sheet) – no layer Transversalis fascia now directly meets the posterior aspect of rectus abdominis muscle Internal aspect of rectus abdominus muscle is in direct contact with the transversalis fascia Thin layer of connective tissue located between posterior surface of the transverse abdominus muscle and the extraperitoneal fat of the parietal peritoneum Transversalis fascia Extraperitoneal fat Parietal peritoneum Layers of the Anterolateral Abdominal Wall Skin/superficial fascia Camper’s fascia Scarpa’s fascia External oblique muscle Internal oblique muscle Transversus abdominis muscle Transversalis fascia Extraperitoneal fat Parietal layer of the peritoneum POSTERIOR ABDOMINAL WALL MUSCLES MUSCLE ATTACHMENT/LOCATION INNERVATION MAIN ACTION/ROLE Quadratus lumborum Origin: iliac crest, iliolumbar ligament Insertion: rib 12, TPs of L1-L4 Ventral rami of spinal nerves T12, L1-L4 Extension of trunk Lateral flexion of trunk Fixes rib 12 during inspiration Psoas Major Origin: bodies and TPs of L1-L5 Insertion: lesser trochanter of femur Lumbar plexus (L1-L3) Flexion of thigh (ipsilateral) Lateral rotation of thigh (ipsilateral) Flexion of trunk (bilateral) Lateral flexion of trunk (ipsilateral) Iliacus Origin: iliac fossa, sacral ala Insertion: lesser trochanter of femur Femoral nerve Flexion of thigh Lateral rotation of thigh INGUINAL CANAL Inguinal canal: oblique canal about 4cm long directing downward and medial-ward; parallel with and above the medial half of the inguinal ligament Extends from deep inguinal ring to the superficial inguinal ring Superficial inguinal ring: triangular gap in the external oblique aponeurosis Deep inguinal ring: oval shaped opening in the fascia transversalis; situated just above midinguinal point and lateral to the stem of the inferior epigastric vessels Contents of the canal: Spermatic cord – containing ductus (vas) deferens, testicular vessels, autonomic nerves and lymphatic Ilioinguinal nerve (in males) Round ligament of uterus and ilioinguinal nerve (in females) Conjoint tendon: formed by fusion of the lowest aponeurotic fibers of the internal oblique and of the transversus abdominus muscles; lies behind superficial inguinal ring and strengthens the abdominal wall at this point (once weakened – makes hernias easier to occur)