The Sciatic nerve is the largest nerve in the human body, measuring almost 2 centimeters in diameter from its origin (1). This large nerve spans the leg from the pelvis to the posterior part of the foot.
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Structure:
The Sciatic nerve is derived from fibre tracts of the sacral plexus from the vertebral roots L4 to S3 inside the pelvic girdle (2). Prior to reaching the Piriformis muscle, the fibres of the sacral plexus combine to form the single Sciatic nerve enclosed within an epineural sheath before it courses through the Greater sciatic foramen, inferior to the Piriformis muscle to exit the pelvis into the gluteal region (3).
Figure 1.1. Picture of the Sciatic nerve arising from L4 to S3.
Before descending the leg, the Sciatic nerve crosses the Gemelli muscles, Obturator internus and the Quadratus muscles. It then traverse down the posterior aspect of the leg between the greater trochanter of the femur and the ischial tuberosity of the pelvis to the popliteal fossa, passing superficially to the expansive Adductor magnus muscle but deep to the long head of the Biceps femoris (4).
Although the exact location of the bifurcation differs between individuals, the Sciatic nerve divides into two main branches: the Tibial nerve and the Common peroneal nerve, commonly just above the popliteal crease (1). While the tibial nerve travels medially through the popliteal fossa, the Common peroneal nerve descends posteriorly to the fibula head before winding laterally along the neck.
Figure 1.2. The Sciatic nerve passing inferiorly to the Piriformis and long head of Biceps femoris.
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Innervations:
Motor:
The Sciatic Nerve’s major innervations are the muscles in the posterior compartment of the thigh. These include: the Biceps femoris short head and long head, Semimembranosis, Semitendinosis muscle (1). Although belonging to the medial compartment, the hamstring portion of the Adductor Magnus is also innervated by this vast nerve. Muscles of the leg, inferior to the knee joint, are also indirectly innervated by the branches of the Sciatic nerve (5).
Figure 1.3. Motor innervation of the Sciatic nerve.
Sensory:
The Sciatic nerve itself do not provide any sensory innervation although its terminal branches are do give off some cutaneous supply to the skin of the lateral leg, and both the dorsal and plantar surfaces of the foot.
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On to Tibial nerve.
Seriously Sciatic 