Pronounced “s-eye-AT-ik-ah”

What is the Sciatic Nerve?
The sciatic nerve is the largest and longest single nerve in the human body, about as big around as a man’s thumb at its largest point.
The nerve originates in the lower spine as nerve roots exit the spinal cord (through gaps in the bones at the back of the spine), and extends all the way down the back of the leg to the toes.
Causes
Sciatica occurs when the sciatic nerve becomes pinched anywhere along its path. It is usually by a herniated disk in your spine or by an overgrowth of bone (bone spur) on your vertebrae.
Damage to or spasm in any muscles close to the nerve can cause the pain of sciatica. Removing the constriction around the pinched nerve decreases and removes the pain signal.
More rarely, the nerve can be compressed by a tumor or damaged by a disease.

Seek immediate medical care if:
- You have sudden, severe pain in your low back or leg and numbness or muscle weakness in your leg
- The pain follows a violent injury, such as a traffic accident
- You have trouble controlling your bowels or bladder
Symptoms – How it feels

Pain that radiates from your lower (lumbar) spine to your buttock and down the back of your leg is the hallmark of sciatica. You might feel the discomfort almost anywhere along the nerve pathway, but it’s especially likely to follow a path from your low back to your buttock and the back of your thigh and calf.
The pain can vary widely, from a mild ache to a sharp, burning sensation or excruciating pain. Sometimes it can feel like a jolt or electric shock. It can be worse when you cough or sneeze, and prolonged sitting can aggravate symptoms. Usually only one side of your body is affected.
Some people also have numbness, tingling or muscle weakness in the affected leg or foot. You might have pain in one part of your leg and numbness in another part.
While the above types of symptoms are common, symptoms can vary depending on a number of factors, such as unique anatomical variances, and the degree and characteristics of the specific pathology.
Sources:
http://www.spine-health.com/conditions/spine-anatomy/sciatic-nerve-anatomy
http://www.mayoclinic.org/diseases-conditions/sciatica/basics/definition/con-20026478