Five spinal nerve roots come together to make up the sciatic nerve, the largest nerve in the human body. The sciatic nerve branches to form both the tibial and common fibular nerves.
Nerve roots are branches of the spinal cord that exit the main cord, as two pairs, at each level of the vertebra. The five nerve roots that combine to form the sciatic nerve emerge from the lumbar and sacral areas of the lower spine. The sciatic nerve extends from the region of the pelvis and down the back of the thigh. Near the back of the knee the sciatic nerve branches to form the tibial and common fibular nerves. The tibial nerve innervates the back of the lower leg, while the fibular nerve serves the front and side. Most of the lower leg and the skin of the foot owe their sensation and movement to the sciatic nerve.
The sciatic nerve is not actually in contact with the spine. When the spine does touch the sciatic nerve it causes sciatica, a type of nerve pain specific to this nerve. Ruptured discs, bone spurs, pinched nerves and arthritis are potential causes of sciatica. Treatment for sciatica typically involves exercise and medication to relieve pain. Given rest and relaxation of the nerve, sciatica often improves or abates completely.