Sciatica is a sharp, tingling sensation, big volt kind pain which is irritated by the sciatic nerve, due to jamming the sciatic nerve. It might be coming from the lower back and/or the hip. It may be various experiences from really painful experience to the tightness of Calf and/or Hamstring muscles, numbness, tingling sensation, etc.
Some patients are complaining from the lower back to hip to lower leg/ankle/foot/toes. Every presentation of the patients are quite different and various, depending upon the severity of damaging Sciatic nerve.
As you can see from above diagram, Sciatic nerve is mainly from L4, L5 lumbar spinal nerves. Usually, from the daily practice, the patients have the problems at the L4, L5 nerve pathway, leading to the jamming the nerve.
Major jamming nerve may be coming from the nerve root.
As you can see from above picture, for example, when the muscle between two transverse processes were contracted and/or spasming and/or cramping, the intervertebral disc is squeezed and bulged. The bulged disc is affecting the nerve root, leading to jamming nerve. The jamming nerve may cause the sciatic pain and/or tightness feeling of Hamstring and/or Calf muscles, numbness, tingling sensations, etc.
The disc bulging also may cause the scoliosis as you can see from above diagram. As you can see above photo, the left side of transversalis muscle is spasmed and the right side of the transversalis muscle is normal. That meaning is that the left side of muscle is pulling to left side, leading to the spinous process is deviated to the left side, making the curve.
However, the piriformis syndrome is quite similar to the sciatica. But actually, it is same kind of pain due to the different reason.