Lumbosacral trunk

Sciatic nerve

The sciatic nerve is the largest nerve in the human body. It arises from the anterior rami of spinal nerves L4-S3, on the anterior surface of the piriformis muscle. This nerve exits the pelvic cavity via the greater sciatic foramen (inferior to the piriformis muscle) into the gluteal region. From here, it runs through the posterior aspect of the thigh to reach the popliteal fossa where it terminates into two large nerve branches: the tibial nerve and the common peroneal nerve.

The sciatic nerve is responsible for motor and sensory innervation of the thigh, leg, and foot. More specifically, this nerve provides motor supply for the muscles of the posterior thigh, a portion of the adductor magnus, muscles of the posterior, anterior, and lateral compartments of the leg and foot muscles. In addition, it provides sensory innervation for the posterior thigh, lateral and posterior leg, as well as the dorsum and sole of foot.

Superior gluteal nerve

The superior gluteal nerve is formed by the dorsal fibers of the spinal nerves L4, L5 and S1. The nerve leaves the pelvis and enters the gluteal region through the greater sciatic foramen (superior to the piriformis muscle). The superior gluteal nerve is a motor nerve that provides innervation for the gluteus medius and gluteus minimus muscles, as well as the tensor fasciae latae. 

Inferior gluteal nerve

The inferior gluteal nerve originates from the dorsal divisions of the spinal nerves L5, S1 and S2. Similar to the superior gluteal nerve, the inferior gluteal nerve also travels to the gluteal region through the greater sciatic foramen (inferior to the piriformis muscle) to innervate the gluteus maximus muscle. 

The nerve to obturator internus and superior gemellus muscles

This nerve is formed by fibers from the anterior divisions of spinal nerves L5, S1 and S2. Similar to other branches of the lumbosacral trunk, this nerve also passes through the greater sciatic foramen (inferior to the piriformis muscle) to innervate the muscles listed in its name: obturator internus muscle and superior gemellus muscle. 

The nerve to quadratus femoris and inferior gemellus muscles

This nerve is formed by the fibers of the anterior divisions of spinal nerves L4, L5 and S1. From its origin in the pelvis, the nerve also enters the gluteal region via the greater sciatic foramen (inferior to the piriformis muscle). It descends along the ischium and terminates by giving off branches to supply the quadratus femoris muscle and the inferior gemellus muscle.