Spinal discs are composed of 3 parts: the top and bottom of the adjacent bones, the jelly center, and the thick ligament which surrounds it. Injuries to the disc generally involve a disruption of the ligament, and movement of the jelly out of a centered position between the bones. This can cause pain, change the way the bones move, or irritate the nerves which lie close to the disc.
Joint problems generally have to do with a loss of the body's ability to sense the position of the joint. These problems are referred to as "segmental" because of the segments, or individual bones, of the spine.
Nerve irritation is on a spectrum between acute and chronic, or short and long term. Acute nerve irritation is generally an chemical inflammatory problem, not a mechanical one. Chronic nerve irritation, on the other hand, is a mechanical problem of scar tissue, known as adhesions, within the nerve itself, or between the nerve and the tissues around it.
Muscle pain generally comes from two sources, trigger points and adhesions. Trigger points are muscle knots that created pain in a consistent pattern, sometimes in a location distant from the muscle. This is one example of a phenomenon known as referred pain. Adhesions in muscles are very similar to those found in nerves. In muscles, adhesions can reduce a muscle's ability to contract or relax, and can create imbalances affecting the joints.