The lumbosacral plexus is a complex network of nerves that arises from the lumbar and sacral spinal nerves (L1 to S4) and supplies the lower extremities, pelvis, and some parts of the abdominal wall. It is formed by the intertwining and branching of multiple nerves, and its main function is to provide motor and sensory innervation to the lower limbs and pelvis. Here’s an overview of the major nerves and components of the lumbosacral plexus:

1. Lumbar Plexus (L1-L4): The lumbar plexus is the upper portion of the lumbosacral plexus and is formed by the ventral rami of the first four lumbar nerves (L1 to L4). It lies within the psoas major muscle and gives rise to several important nerves, including:

• Iliohypogastric nerve (L1): Provides motor innervation to the transversus abdominis and internal oblique muscles, and sensory innervation to the skin of the lower abdomen.
• Ilioinguinal nerve (L1): Supplies the skin of the upper medial thigh, the mons pubis, and the labia majora in females or the root of the penis and scrotum in males.
• Genitofemoral nerve (L1-L2): Divides into two branches – the genital branch, which supplies the cremaster muscle in males and sensory innervation to the scrotum or labia majora, and the femoral branch, which provides sensory innervation to the skin of the upper anterior thigh.
• Lateral femoral cutaneous nerve (L2-L3): Supplies sensory innervation to the lateral thigh.
• Femoral nerve (L2-L4): The largest nerve of the lumbar plexus, it provides motor innervation to the quadriceps femoris muscle group, sartorius, and iliacus muscles, and sensory innervation to the anterior thigh and medial leg and foot.

2. Sacral Plexus (L4-S4): The sacral plexus is the lower portion of the lumbosacral plexus and is formed by the ventral rami of the last lumbar nerve (L4) and the sacral nerves (S1 to S4). It lies on the posterior aspect of the pelvis and gives rise to the following major nerves:

• Superior gluteal nerve (L4-S1): Supplies the gluteus medius, gluteus minimus, and tensor fasciae latae muscles, which are responsible for hip abduction and medial rotation.
• Inferior gluteal nerve (L5-S2): Innervates the gluteus maximus muscle, responsible for hip extension and lateral rotation.
• Sciatic nerve (L4-S3): The largest nerve in the body, it is formed by the fusion of the ventral rami of L4 to S3. The sciatic nerve runs down the posterior thigh and divides into two terminal branches – the tibial nerve and the common fibular (peroneal) nerve.
• Tibial nerve (L4-S3): Supplies the posterior thigh muscles and almost all the muscles in the leg and foot, controlling ankle plantar flexion and foot inversion.
• Common fibular (peroneal) nerve (L4-S2): Divides into the superficial fibular nerve and the deep fibular nerve. It controls dorsiflexion of the foot and the muscles of the anterior and lateral leg.