The sciatic nerve is the largest and longest nerve in the human body. Every person has 2 sciatic nerves, the right and left nerves—supplying each lower limb.
The sciatic nerve originates in the lower spine and is formed by the combination of spinal nerves L4 to S3. The sciatic nerve is responsible for motor and sensory functions of the lower body.
Origin and Branches of the Sciatic Nerve
The sciatic nerve starts in the lower spine and follows a long path through the buttock, down the back of the thigh and leg, and finally ends in the foot.
The sciatic nerve is formed by the combination of 5 nerves in the lumbar (lower) and sacral spineL4, L5, S1, S2, and S3. These nerve fibers are typically responsible for motor and sensory functions of the lower body. The 5 nerves group together near the front surface of the piriformis muscle deep in the buttock and form the large, thick sciatic nerve. At its thickest portion, the nerve measures around 2 cm in diameter.
The nerve leaves the pelvis along with its surrounding nerves and blood vessels through the greater sciatic foramen below the piriformis muscle. It progresses downward between the muscles of the thigh and is surrounded by a single long fatty sheath from the pelvis to the knee, where it divides. In around 10% of the population, the nerve may divide above the knee.
At the popliteal fossa near the back of the knee, the sciatic nerve divides into 2 main branches: the tibial nerve and the common peroneal nerve. The popliteal fossa is a rhomboid-shaped space that serves as a conduit for blood vessels and nerves in the leg.
The tibial nerve continues down the back of the leg to the heel and sole of the foot.
The common peroneal travels sideways along the outer part of the knee to the outer border of the leg