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The Lumbar Plexus
Directly from Dr. T's review notes
Question | Answer |
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What (dorsal/ventral, levels) is the Lumbar Plexus? | The Lumbar Plexus arises from Ventral Primary Rami (VPR) of L1 L2 L3 L4 with a small contribution from the subcostal nerve (T12). |
From most cephalad moving caudally, what are the three nerves that arise from VPR of L1 & L2 and transmit both motor and cutaneous sensory information from the areas roughly described by their names? | Iliohypogastric, Ilioinguinal, Genitofemoral |
What are the cutaneous and muscular components of the Iliohypogastric Nerve? | Cutaneous: Skin over the lateral gluteal region and above the pubis Muscular: internal and transverse abdominal muscles |
What are the cutaneous and muscular components of the Ilioinguinal Nerve? | Cutaneous nerve, only (unless it combines with the iliohypogastric nerve): Skin over the root of the penis and upper part of the scrotum (male), skin covering the mons pubis and labia majora (female) |
What does the genital branch of the Genitofemoral Nerve pass through and enter? | The genital branch passes through the deep inguinal ring and enters the inguinal canal. |
What are the male muscular and cutaneous components of the genital branch of the Genitofemoral Nerve? | Cremaster muscle (Note: cremasteric reflex, which describes contraction of the cremasteric muscle when the skin of the superior medial part of the thigh is touched). In men, the genital branch continues down and supplies the scrotal skin. |
What are the female cutaneous components of the Genitofemoral Nerve? | In women, the genital branch accompanies the round ligament of uterus, terminating in the skin of the mons pubis and labia majora. |
What are the cutaneous portions of the femoral branch of the Genitofemoral Nerve? | The femoral branch passes underneath the inguinal ligament, travelling adjacent to the external iliac artery, and supplying the skin of the upper, anterior thigh. |
The intrinsic back muscles are derived from the epimere, but the Quadratus Lumborum is derived from hypomere as are all the muscles of the body wall and limbs. What is the QL innervated by? | The QL is innervated by the VPR of T12-L4.(Odd bc back m. & not DPR) This muscle too, can be involved in low pain back associated with acute and repetitive trauma as well as poor posture, poor breathing technique, and other sedentary lifestyle habits. |
What are he major branches of the lumbar plexus and what levels do they arise from ...? (VRP/DRP, levels) | All VPR; Lateral Femoral Cutaneous Nerve (L2 L3 posterior divisions), The Nerves to the Iliacus and Psoas (L2-4 posterior divisions), The Femoral Nerve (L2-4, posterior divisions), The Obturator Nerve (L2-4, Anterior Divisions) |
Describe The Lateral Femoral Cutaneous Nerve (L2, 3 POSTERIOR DIVISIONS(still VPR)) | A purely cutaneous nerve, it supplies the skin of the superior anterior and lateral thigh. It arises from VPR of L2, 3. Clinical significance: Meralgia Paresthetica. |
Describe The Nerves to the Iliacus and Psoas (L2-4 POSTERIOR DIVISIONS(still VPR)) | Muscular branches to iliacus & psoas muscles. Since these muscular brs. are the first branch off the confluence of L2, 3, 4, and the femoral n. is the only continuation, you may see resources consider these mm. innervated by the 1st brs. of femoral n. |
Describe the cutaneous components of the Femoral Nerve (L2-4, POSTERIOR DIVISIONS) (Femoral Nerve is the largest branch of lumbar plexus) | Anterior cutaneous branches: anterior thigh; Saphenous nerve: medial knee, leg, and medial foot (from L4, mainly). |
Describe the muscular branches of the Femoral Nerve (L2-4, POSTERIOR DIVISIONS) (Femoral Nerve is the largest branch of lumbar plexus) | -muscles that flex the thigh at the hip: pectineus (L2, 3), iliopsoas (L2-4), sartorius (L2, 3), rectus femoris (L2-4), -muscles that extend the leg at the knee: quadriceps femoris (L2-4). |
Where is the cutaneous branch of the Obturator Nerve (L2-4, ANTERIOR DIVISIONS)? | Medial thigh |
What are the muscular branches of the Obturator Nerve (L2-4, ANTERIOR DIVISIONS)? | Obturator externus (L3, 4), Adductor longus (L2-4), Adductor brevis (L2-4), Gracilis (L2-4), Pectineus (L2, 3), Adductor magnus, anterior portion (L2-4). (Note: the pectineus may be innervated by either the femoral nerve or the obturator nerve). |
Describe the path of the Obturator nerve (L2-4, ANTERIOR DIVISIONS) | The obturator nerve passes posterior to the psoas and anterior to the SI joint and then courses inferior and anterior to pass through the obturator foramen via the obturator tunnel. |