A bulging disc is caused when the nucleus (soft jelly-like material inside of a disc swells and puts excess pressure on the annulus (the thicker, fibrous outer portion of the disc).

Many adults walking around may have a small bulged disc in their back with no symptoms. Typically, most bulged discs will heal on their own. When a bulged disc is putting pressure on a nerve, either from physical swelling or from increased inflammation, the nerve pressure causes pain. 

A herniated disc is a bulged disc where the nucleus (jelly-like center of the disc) has pushed through a tear in the annulus (the thicker, fibrous outer portion of the disc). Herniated discs can heal without surgery but it is important to reduce the swelling from the herniated disc as well as the inflamed nerve. 

Stenosis is a narrowing of an opening. Spinal stenosis is cause when a vertebrae wears down and degenerates over time. The openings where the nerve exits the spine to reach other parts of the body gets smaller and puts pressure on the nerves. The pressure on the nerve causes pain. 

Sciatica is a sharp shooting pain down one of both legs. It is cause by pressure on the lower nerves leaving the lower back. Bulging or herniated discs or spinal stenosis can all play a roll in sciatica symptoms.