The Science Behind Pain

Physiology of Pain – Chronic or persistent pain (it’s different from acute injury or pain)

In the previous post, we began the journey down the road of pain. You can go back and read it here.

When these systems have to work for longer periods (as in persistent or chronic pain) the sensors in the spinal cord are overloaded with stimuli and send “mixed” messages to the brain. The “alarm system” in your brain becomes altered, and things that used to hurt now hurt more (called hyperalgesia); while things that didn’t hurt before also hurt (called allodynia.) Basically, the brain is being told that there is more danger at the tissues than there actually is. The area of the brain associated with the part of the body that is injured becomes “smudged” and signals sent to that area of the body are altered.

As pain persists it begins to dominate all aspects of life — work, friendships, family life, hobbies, thoughts, sports, emotions, devotions, beliefs, etc. The persistence of the pain affects the systems of your body and changes in these systems can combine to perpetuate the pain.  It can be altered so much that thinking about a movement or watching another person perform a movement can increase pain. In fact, as pain persists, the pain can “spread” to other areas of the body that have not been injured, which is called “central sensitization.” In other words, there are no “fences” within the nervous system. This goes back to the brain being told that there is more damage in the tissues (and in different areas of the body) then there actually are. Central sensitization can be part of the issue in conditions such as fibromyalgia, myofascial pain syndrome, chronic fatigue syndrome, and other diagnoses.

When the body has persistent or chronic pain it can affect the muscles and keep them in a constant state of “readiness” (remember, one of the body’s responses to pain is to activate systems to help get the body out of pain, which includes the musculoskeletal system). When the “alarm system” in the brain gets altered those muscles, which are not normally designed to work for long periods, stay in a constant state of readiness and tighten up. The tightness causes a build up of acid in the muscles, which in turn may lead to further pain; the tightness of these muscles may notreturn to normal once the threat to the body has been removed. The change in muscle function affects movement patterns and postures. The body moves less efficiently and more stress is put on areas of the body that are not designed to take them.  Once the body learns new motor patterns, they can be very hard to reverse.

Knowing about pain is helpful. Having strategies for managing your pain is more helpful. The next post will get into management strategies.

(The information presented here has been adapted from Butler and Moseley. Explain Pain.2008.)