Anatomy study note · Abdomen

Lumbar plexus

Formed within the psoas by the anterior rami of L1–L4. Its branches supply the lower abdominal wall and much of the lower limb.

Key points

• L1–L4 in the psoas.
• Lateral border: iliohypogastric, ilioinguinal, lateral cutaneous of thigh, femoral.
• Medial border: obturator + lumbosacral trunk. Front: genitofemoral.
• Genitofemoral → cremasteric reflex.
• Ventral root: basal-lamina neurons. Dorsal root: neural-crest ganglion cells.
• Schwann cells: neural crest.
• Nerve: epineurium → perineurium (blood–nerve barrier) → endoneurium.
• Cut nerve: Wallerian degeneration; regrows 0.5–3 mm/day.

The full note in the atlas also covers

Branches · Histology · Development · Clinical notes

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Written from

• Snell’s Clinical Anatomy by Regions, 10th ed., ch. 7, PDF pp. 944, 967–970
• Inderbir Singh’s Human Embryology, ch. 17, PDF pp. 318, 321, 323–325; ch. 10, PDF p. 144
• BRS Cell Biology & Histology, 7th ed., ch. 9, PDF pp. 163–166, 171–172

More from the abdomen

• Pancreas
• Peritoneum
• Portal vein
• Psoas major
• Pyramidalis
• Quadratus lumborum
• Rectus abdominis
• Renal arteries and veins
• Spleen
• Stomach
• Superficial epigastric vessels
• Superior mesenteric artery

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