Psoas major muscle
The psoas major 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. In less than 50 percent of human subjects[1] the psoas major is accompanied by the psoas minor. In mice, it is mostly a fast-twitching, type II muscle,[2] while in human it combines slow and fast-twitching fibers.[3]
Location
Origin
The psoas (\ˈsō-əs\) 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 neighboring invertebral discs. The lumbar plexus lies between the two layers.[1]
Insertion
Joined by the iliacus, psoas major forms 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 bone from the muscle at the level of the iliopubic eminence. The iliac subtendinous bursa lies between the lesser trochanter and the attachment of the iliopsoas.[1]
Innervation
Innervation of the psoas major is through the anterior rami of L1 to L3
Function
As part of the iliopsoas, psoas major contributes to flexion and external rotation in the hip joint. On the lumbar spine, unilateral contraction bends the trunk laterally, while bilateral contraction raises the trunk from its supine position.[4]
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.
For example, when doing a situp that brings the torso (including the lower back) away from the ground and towards the front of the leg, the hip flexors (including the iliopsoas) will flex the spine upon the pelvis.
Due to the frontal attachment on the vertebrae, rotation of the spine will stretch the psoas.
Tightness of the psoas can result in lower back pain by compressing the lumbar discs.[5]
See also
Notes
- ^ a b c Platzer (2004), p 234
- ^ Nunes, MT; Bianco, AC; Migala, A; Agostini, B; Hasselbach, W (1985). "Thyroxine induced transformation in sarcoplasmic reticulum of rabbit soleus and psoas muscles". Zeitschrift fur Naturforschung. Section C: Biosciences 40 (9–10): 726–34. PMID 2934902.
- ^ Arbanas, Juraj; Starcevic Klasan, Gordana; Nikolic, Marina; Jerkovic, Romana; Miljanovic, Ivo; Malnar, Daniela (2009). "Fibre type composition of the human psoas major muscle with regard to the level of its origin". Journal of Anatomy 215 (6): 636–41. doi:10.1111/j.1469-7580.2009.01155.x. PMID 19930517.
- ^ Thieme Atlas of Anatomy (2006), p 422
- ^ Akuthota, et all(2008). p 40
References
Additional images
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Right femur. Anterior surface.
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Diagram of a transverse section of the posterior abdominal wall, to show the disposition of the lumbodorsal fascia.
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The diaphragm. Under surface.
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Muscles of the iliac and anterior femoral regions.
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The arteries of the pelvis.
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The relations of the femoral and abdominal inguinal rings, seen from within the abdomen. Right side.
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The thoracic and right lymphatic ducts.
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The lumbar plexus and its branches.
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Nerves of the right lower extremity. Front view.
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Sacral plexus of the right side.
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Transverse section, showing the relations of the capsule of the kidney.
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External links
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
