The intervertebral disk is part of the joint between each of the bones, or vertebra, of the spine. The intervertebral disks cushion the joints and allow them to move correctly. They have a tough, fibrous outer layer and a gel-like inner layer. An annular tear occurs when degeneration or injury causes the outer layer to tear. This is typically painful because there are nerves within the outer layer that are irritated by the exposure to the material in the inner layer.