Controls the muscles of the back of the knee and lower leg. It also provides sensation to the back of the thigh, part of the lower leg, and the sole of the foot.
Damage to, or irritation of, the sciatic nerve at any point can result in a number of symptoms, some of them potentially serious. The malady we call sciatica is the result of inflammation of the sciatic nerve, usually caused by chronic irritation of one or more of the spinal nerves L4  S4. Sciatica is pain, tingling, or numbness produced by an irritation of the nerve roots that lead to the sciatic nerve. The sciatic nerve is formed by the nerve roots coming out of the spinal cord into the lower back. It goes down through the buttock, then its branches extend down the back of the leg to the ankle and foot. The most common cause of sciatica is a bulging or ruptured disc (herniated disc) in the spine pressing against the nerve roots that lead to the sciatic nerve. Any problem in the lower spine can affect a nerve that feeds into the sciatic nerve, causing sciatica symptoms. Watch: Sciatica Animated Video. Any problem in the lower spine can affect one of the nerves that feeds into the sciatic nerve, causing pain to radiate along that part of the nerve. The main nerve traveling down the leg is the sciatic nerve. Pain associated with the sciatic nerve usually originates when nerve roots in the spinal cord become compressed or damaged. Symptoms can include tingling, numbness, or pain that radiates to the buttocks, legs, and feet. Sciatica occurs when there is pressure or damage to the sciatic nerve. This nerve starts in the lower back and runs down the back of each leg. This nerve controls the muscles of the back of the knee and lower leg. It also provides sensation to the back of the thigh, part of the lower leg, and the sole of the foot. A variety of lower back conditions may lead to sciatica. Most commonly, a lumbar herniated disc will cause sciatic nerve pain. Other common disorders that cause sciatic pain include lumbar degenerative disc disease, spondylolisthesis, spinal stenosis, or osteophytes and arthritis in the spine.
http://www.unm.edu/~toolson/sciatic_nerve.html http://www.webmd.com/back-pain/tc/sciatica-topic-overview http://www.webmd.com/back-pain/tc/sciatica-topic-overview http://www.spine-health.com/conditions/spine-anatomy/sciatic-nerve-anatomy http://umm.edu/health/medical/reports/articles/back-pain-and-sciatica https://www.nlm.nih.gov/medlineplus/ency/article/000686.htm http://www.spine-health.com/conditions/sciatica/types-sciatic-nerve-pain
what does sciatic nerve do