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Questions and Answers
What is the primary action of the psoas major muscle?
What is the primary action of the psoas major muscle?
- Abduction of the thigh
- Flexion and medial rotation of the thigh (correct)
- Extension of the thigh
- Lateral rotation of the thigh
Which statement about the psoas minor is correct?
Which statement about the psoas minor is correct?
- It originates from the sides of the 12th thoracic vertebra. (correct)
- It primarily assists in the extension of the lumbar spine.
- It has a strong contribution to the flexion of the hip.
- It is always present in humans.
From where does the psoas major muscle originate?
From where does the psoas major muscle originate?
- Pelvic bones
- Coccyx and sacrum
- Lower ribs
- Thoracic to 5th lumbar vertebrae (correct)
Which muscle is associated with the iliopubic eminence?
Which muscle is associated with the iliopubic eminence?
What is the nerve supply for the psoas major muscle?
What is the nerve supply for the psoas major muscle?
What is the primary action of the Iliacus muscle?
What is the primary action of the Iliacus muscle?
Which nerve supplies the Quadratus Lumborum muscle?
Which nerve supplies the Quadratus Lumborum muscle?
Where does the Iliacus muscle primarily originate?
Where does the Iliacus muscle primarily originate?
Which statement accurately describes the Quadratus Lumborum muscle's role during respiration?
Which statement accurately describes the Quadratus Lumborum muscle's role during respiration?
What contributes to the formation of the lumbar plexus?
What contributes to the formation of the lumbar plexus?
What spinal segments primarily contribute to the formation of the lumbar plexus?
What spinal segments primarily contribute to the formation of the lumbar plexus?
Which nerve is responsible for innervating the anterior thigh muscle?
Which nerve is responsible for innervating the anterior thigh muscle?
Which of the following nerves does NOT arise from the lumbar plexus?
Which of the following nerves does NOT arise from the lumbar plexus?
What is the function of the obturator nerve?
What is the function of the obturator nerve?
Which of the following nerves is formed from roots L2 and L3 and innervates the lateral aspect of the thigh?
Which of the following nerves is formed from roots L2 and L3 and innervates the lateral aspect of the thigh?
Which structure does the lumbar plexus primarily lie within?
Which structure does the lumbar plexus primarily lie within?
Which nerves supply the external genitals?
Which nerves supply the external genitals?
What is the contribution of the lumbosacral trunk to the lumbar plexus?
What is the contribution of the lumbosacral trunk to the lumbar plexus?
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Study Notes
Psoas Major
- Originates from the thoracic and lumbar vertebrae, extending from the transverse processes, vertebral bodies, and intervertebral discs
- Inserts into the lesser trochanter of the femur.
- Supplied by the lumbar plexus (L2-4)
- Primarily responsible for flexing and medially rotating the thigh, and flexing the trunk when the thigh is fixed.
Psoas Minor
- May be absent in up to 40% of individuals.
- Long and slender, originates from the 12th thoracic and 1st lumbar vertebrae as well as the disc between them.
- Inserts into the iliopectineal eminence of the hip bone.
- Supplied by a branch from the 1st lumbar nerve.
- Acts as a weak flexor of the lumbar vertebral column.
Iliacus
- Located in the false pelvis, separate from the psoas muscles.
- Originates from the upper 2/3 of the iliac fossa, the inner lip of the iliac crest, and the iliolumbar ligament.
- Inserts into the lesser trochanter of the femur, joining the tendon of the psoas major to form the iliopsoas muscle.
- Supplied by the femoral nerve within the abdomen.
- Responsible for flexing and medially rotating the thigh, as well as assisting in flexing the trunk when the thigh is fixed.
Quadratus Lumborum
- Flat, quadrilateral-shaped muscle located alongside the vertebral column and lateral to the psoas major.
- Originates from the iliolumbar ligament, the adjoining part of the iliac crest, and the tips of the transverse processes of the lower lumbar vertebrae.
- Inserts into the lower border of the 12th rib and the transverse processes of the upper four lumbar vertebrae.
- Supplied by the lumbar plexus (T12 and L1, 2, 3, 4).
- Primarily responsible for fixing or depressing the 12th rib during respiration and laterally flexing the vertebral column towards the same side.
Lumbar Plexus
- Formed by the anterior rami of the upper four lumbar nerves as well as a contribution from the T12 (subcostal) nerve.
- Lies within the psoas major muscle and interacts with the sympathetic plexus.
- The lumbar plexus provides innervation to the lower abdominal wall, external genitalia, hip, thigh, and the medial part of the leg.
Nerves of Lumbar Plexus
- Subcostal (T12)
- Iliohypogastric (L1)
- Ilioinguinal (L1)
- Genitofemoral (L1, L2)
- Lateral cutaneous nerve of the thigh (L2,3)
- Femoral nerve (L2,3,4)
- Obturator nerve (L2,3,4)
- Accessory obturator nerve (L3,4)
- Lumbosacral trunk (L4,5)
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