Figure 14-1
Lumbar (T12-L4) and sacral (L4-S5) plexuses.

The lumbosacral plexus can be described as a combination of spinal nerve ventral rami from the lumbar plexus T12 - L4 and the sacral plexus, L4 - S5. These nerve plexuses are connected by a portion of L4 and all of L5 called the lumbosacral trunk. These nerves serve the anterior abdominal wall, the genitals, the perineum, the hip intrinsic muscles, the gluteal muscles and the entire lower limb . (Figure 14-1)

Like the brachial plexus, the lumbosacral plexus has anterior and posterior divisions serving anterior and posterior muscles, joints and skin - but not like you may think!

During fetal development, our lower limbs rotate medially and drag their nerve supply with them. Thus the extensor muscles are located on the anterior side of the lower limb and the flexor muscles are found on the posterior side of the limb. The upper limb has rotated just opposite - i.e., to the lateral side, consequently, the flexor muscles are found on the anterior surface of that limb.

So, for example, is the femoral nerve composed of anterior division nerves or posterior division nerves? Right! - posterior division nerves of ventral rami of spinal nerves L2, L3 and L4.

We outline the two plexuses like this:

• Lumbar Plexus:
• subcostal - T12
• iliohypogastric - L1
• ilioinguinal - L1
• lateral cutaneous of the thigh - L2-L3
• genitofemoral - L1-L2
• femoral nerve - L2 - L4
• obturator nerve - L2 - L4
• lumbosacral trunk - L4 - L5
• Sacral Plexus:
• superior gluteal nerve - L4 - S1
• inferior gluteal nerve - L5 - S2
• sciatic nerve
• tibial nerve - L4 - S3
• peroneal nerve - L4 - S3
• nerves to the hip intrinsics - L4- S2
• pudendal nerve - S2 - S4
• posterior cutaneous nerve of the thigh - L2-L5

These spinal nerves also give rise to parasympathetic fibers to the pelvic viscera, and sympathetic fibers to the pelvic viscera and the lower limb.