The discs are located between each boney vertebrae on the spine.   The disc are flexible and allow greater movement of the spine so we can function properly.  The discs are made up of a harder outer structure called the annulus.  The annulus basically looks like the rings of a tree and is made of of collagen.   The very centre of the disc has a soft jelly liek structure called the nucleus.   It is the nucleus that bulges out or prolapses when given the opportunity.   The ooprtunity arises when there are tears in the annulus or the annulus has simply stretched over time.  The picture above and below show herniated discs which is the next step beyond a simple bulging disc.

A bulging disc or even a herniated disc does not neccessarily mean you will have pain or symptoms.   Around 70% of those aged 21 years old have bulging discs with only around 5% of these having symptoms.   Only in the extreme cases can Practitioners be certain that this is the cause of your symptoms.

A disc “protrusion”,also known as a disc bulge is a condition in which the outermost layers of the annulus fibrosus of the disc are still intact, but can bulge when the disc is under pressure. In contrast to a herniation, none of the nucleus pulposus (soft jelly like inner core of the disc) escapes beyond the outer layers.

Spinal disc herniation may be due to repeated microtrauma, major trauma, lifting injuries, or idiopathic (unknown) causes, in which a tear in the outer, fibrous ring (annulus fibrosus) of an intervertebral disc (discus intervertebralis) allows the soft, central portion (nucleus pulposus) to bulge out beyond the damaged outer rings. Tears are almost always postero-lateral in nature owing to the presence of the posterior longitudinal ligament in the spinal canal. This tear in the disc ring may result in the release of inflammatory chemical mediators which may directly cause severe pain, even in the absence of nerve root compression.  This si known as Internal Disc Degrangement (IDD)