Long answer: Any joint can produce a noise if moved quickly enough. We've discussed why joints make a cracking or popping sound, why people tend to associate the chiropractic adjustment with "the noise", and why the Activator instrument does not cause joints to crack.
There is no doubt that some people find relief from minor aches and pains by cracking their own joints. Unfortunately, this relief is temporary and does not fix the underlying cause of the pain. This means that most self-crackers have to continually crack their own necks or backs many times a day, every day. In this video, a young man cracks his own joints in a rather violent way.
As previously discussed, the crack comes from a joint that is hypermobile (the joint moves too much). However, when a joint is subluxated and interfering with the nervous system, it is usually hypomobile (the joint doesn't move enough). The specific chiropractic adjustment targets the hypomobile joint and reintroduces motion into the fixed joint. The restored motion is what causes the pain to subside as proper nervous system communication resumes and local inflammation decreases.
There is a very definite relationship between hypermobile and hypomobile joints. Each human body knows its own capabilities, limitations, and normal ranges of motion in all directions. When one vertebral joint in the multijointed neck becomes fixed, the body attempts to compensate for that loss of motion by causing the two neighboring joints (the one above and the one below) to move more than they should. This keeps the same amount of motion in the neck as a whole, but in reality three joints are now in early states of injury.
This young man was experiencing minor pain because of one or more hypomobile joints in his neck. Without stopping to analyze the problem, he instinctively knew that some joints were "stuck" and needed healthy motion. In attempting to self-correct those fixed joints, he whipped his head around. But since his motion was global (involving all of the neck vertebrae), the cracking sound he produced were from the nearby hypermobile joints, not the hypomobile joints he was attempting to correct.
But he still feels relief because of an interesting phenomenon called "pain-gating." This is a simple process whereby the brain is fooled into focusing on something other than the annoying ache or pain from the hypomobile joint. In this case, the brain suddenly receives a flood of information from the proprioceptive nerves* surrounding the hypermobile joints, and temporarily "forgets" about the pain in the hypomobile joint. But this relief is shortlived, because those nerve messages will eventually disppear, and the brain is once again free to concentrate on the pain messages from the hypomobile joint.
Chiropractic is effective because of the specificity of the high-velocity, low-amplitude adjustment. Only the hypomobile joint is targeted, not all the vertebrae of the neck. Only the tense muscles are stretched, not all the muscles of the neck. The healthy joints and hypermobile joints are protected from further injury in the chiropractic adjustment (whereas in the video above, the young man might easily cause himself further injury in his haste to find temporary relief).
There is an old wives' tale that said that if you crack your own knuckles, you'll end up with arthritis. This concept was naturally extended to neck arthritis, back arthritis, and so on. A famous study from 1990 was intended to debunk this myth, since the mechanism behind the various types of arthritis have little to do with joint cracking, though the hand-crackers of the study tended to develop hand swelling and weakened hand muscles. And of course, the neck is a much more complicated structure than a single finger knuckle, so the jury may still be out on the issue of long-term injury.
When you feel tempted to crack your own neck or back, remember that you'll probably be "cracking" the wrong vertebrae. Instead, let your body tell you what it needs: the "I need to crack my neck" feeling is a perfect opportunity to contact your friendly local Peoria chiropractor and get the problem analyzed by a professional and fixed the right way right away.
*Proprioceptive nerves tell your body where each joint is located in space at any given time. When a joint is moved, these special nerves immediately bombard the brain with important information. These proprioceptive nerves allow you to ascend or descend a staircase without looking at your feet, run on uneven ground, or pick up a water glass with your eyes closed. Proprioceptive nerves are especially concentrated in the neck.