The human spine consists of a number of small bones  (called vertebrae) jointed together to form a flexible spinal column. 

This allows a high degree of free movements for our back for performing various activities. 

In between each individual vertebra, there is a disc of soft material (called inter-vertebral disc) to absorb the shock imposed on the spine and to minimize the wear and tear of the vertebrae.

Along the spinal column, there is a "hollow space" for the spinal chord to run through (from the brain down to the lower back). 

Pairs of nerve roots branch out along the Spinal Chord o various parts of our body through the notches at each piece of the vertebrae.

The Spinal Chord and the Nerve Roots are so situated that they can easily compressed by the other component parts (such as the inter-vertebral discs or the vertebrae) when something goes wrong, such as the dislocation of any of those parts (e.g. when slipped disc occurs).