Anatomy, Sciatic Nerve

Excerpt

The sciatic nerve is the largest nerve in humans, originating in the lower back and traveling posteriorly through the lower limb as far down as the heel of the foot. The sciatic nerve innervates a significant portion of the skin and muscles of the thigh, leg, and foot.

The nerve originates from the ventral rami of spinal nerves L4 through S3 and contains fibers from both the posterior and anterior divisions of the lumbosacral plexus. After leaving the lower vertebrae, the nerve fibers converge to form a single nerve. It exits the pelvis through the greater sciatic foramen inferior to the piriformis muscle along with the pudendal nerve and vessels, inferior gluteal nerve and vessels, nerve to obturator internus, and posterior femoral cutaneous nerve. The sciatic nerve then progresses down the posterior compartment of the thigh deep to the long head of the biceps femoris muscle, superficial to adductor magnus and short head of the biceps femoris muscle, and laterally to semitendinosus and semimembranosus muscles.

Just before reaching the popliteal fossa, it divides into two important branches. One branch is the tibial nerve, which continues to descend in the posterior compartment of the leg and foot. The other branch is the common peroneal nerve, which travels down the lateral and anterior compartments of the leg and foot. Until this division occurs, the medial component is referred to as the tibial division or the common fibular (peroneal) division of the sciatic nerve.