The lumbosacral plexus arises from the lumbar, and sacral spinal nerves, providing innervation to the abdomen, pelvis, and lower limb of the body.

Figure 1. The lumbosacral plexus

Parts and origin

As its name suggests, the lumbosacral plexus consists of two parts — the lumbar plexus, and the sacral plexus.

  • Lumbar plexus: L1-L3 (with contributions from the lower part of T12, and the upper part of T4).
  • Sacral plexus: L4-S4

Lumbar plexus

As it forms, it merges with the origin of the psoas major muscle and then branches out to four parts:

  • Under the kidneys (iliohypogastric and ilioinguinal nerves)
    • Both nerves rise from the L1 spinal nerve and enter between the abdominal muscles.
    • The iliohypogastric nerve passes between and innervates the transversus abdominis and internal oblique muscles, with terminal branches innervating the abdominal skin.
    • The ilioinguinal nerve passes between the abdominal muscles to blend with the spermatic cord, passing through the inguinal canal, innervating the skin of the scrotum and the medial

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