Psoas major muscle

The psoas major (/ˈsoʊ.əs/ or /ˈsoʊ.æs/) (from Greek: ψόας – psóās: 'of the loins', genitive singular form of ψόα – psóa 'the loins') is a long fusiform muscle located on the side of the lumbar region of the vertebral column and brim of the lesser pelvis. It joins the iliacus muscle to form the iliopsoas.Position of psoas major muscle. Animation. Hip bones are shown in semi-transparent.Horizontal disposition of the peritoneum in the lower part of the abdomen. (Psoas major labeled at bottom left.)Right femur. Anterior surface.Diagram of a transverse section of the posterior abdominal wall, to show the disposition of the lumbodorsal fascia.The diaphragm. Under surface.Muscles of the iliac and anterior femoral regions.The arteries of the pelvis.The relations of the femoral and abdominal inguinal rings, seen from within the abdomen. Right side.The thoracic and right lymphatic ducts.The lumbar plexus and its branches.Nerves of the right lower extremity. Front view.Sacral plexus of the right side.Transverse section, showing the relations of the capsule of the kidney.Psoas major musclePsoas major musclePsoas major muscle The psoas major (/ˈsoʊ.əs/ or /ˈsoʊ.æs/) (from Greek: ψόας – psóās: 'of the loins', genitive singular form of ψόα – psóa 'the loins') is a long fusiform muscle located on the side of the lumbar region of the vertebral column and brim of the lesser pelvis. It joins the iliacus muscle to form the iliopsoas. The psoas major is divided into a superficial and deep part. The deep part originates from the transverse processes of lumbar vertebrae I-V. The superficial part originates from the lateral surfaces of the last thoracic vertebra, lumbar vertebrae I-IV, and from the neighboring intervertebral discs. The lumbar plexus lies between the two layers. The iliacus and psoas major form the iliopsoas, which is surrounded by the iliac fascia. The iliopsoas runs across the iliopubic eminence through the muscular lacuna to its insertion on the lesser trochanter of the femur. The iliopectineal bursa separates the tendon of the iliopsoas muscle from the external surface of the hip joint capsule at the level of the iliopubic eminence. The iliac subtendinous bursa lies between the lesser trochanter and the attachment of the iliopsoas. Innervation of the psoas major is through the anterior rami of L1 to L3 nerves. In less than 50 percent of human subjects, the psoas major is accompanied by the psoas minor. In mice, it is mostly a fast-twitching, type II muscle, while in human it combines slow and fast-twitching fibers. This muscle is equivalent to the tenderloin. The psoas major joins the upper body and the lower body, the axial to the appendicular skeleton, the inside to the outside, and the back to the front. As part of the iliopsoas, psoas major contributes to flexion in the hip joint. On the lumbar spine, unilateral contraction bends the trunk laterally, while bilateral contraction raises the trunk from its supine position. In addition, attachment to the lesser trochanter, located on the postero-medial aspect of the femur, causes lateral rotation and weak adduction of the hip. It forms part of a group of muscles called the hip flexors, whose action is primarily to lift the upper leg towards the body when the body is fixed or to pull the body towards the leg when the leg is fixed.