Final answer:
The lumbosacral trunk is formed by the ventral rami of spinal nerves L4 and L5, contributing to the sacral plexus and the origin of the sciatic nerve.
Step-by-step explanation:
The lumbosacral trunk is formed by the ventral rami of spinal nerves L4 and L5. This trunk is significant as it contributes to the formation of the sacral plexus, from which the major systemic nerve, the sciatic nerve, arises. The sacral plexus is instrumental in innervating the lower limb, with the sciatic nerve being particularly associated with the condition known as sciatica, where compression or irritation can cause pain that radiates along the path of this nerve.