First we should know more about spinal column, intervertebral discs and sciatic nerve
Spinal column consists of more than 30 smaller bones which are collectively called the vertebrae and which are interlocked and positioned on top of each other. The spaces between the vertebrae are called discs. A disc is similar to a jelly-like fibrocartilage pillow which is elastic and can change shape. In a way, a disc acts like a fender for the intervertebral joints.
If the spine receives great straining or severe shocks, tears may appear on the discs causing the chemicals inside the discs to slip into the spinal canal and spinal cord nerves (spinal disc herniation) and in turn this will lead to the exertion of a great pressure on the spinal cord nerves. The most important of these nerves in the spine is called the “sciatic nerve”, also known as the large nerve.