PAIN "101"

THE CHRONIC PAIN CONTROL WORKBOOK says that the experience of pain is not a simple cause-and-effect relationship between the body and the brain. Rather, it is a complex web of pain signals, chemical messengers, emotions, and thoughts involving several different pathways of pain.
These pathways can transmit the pain signal either at lightning speed or slowly and continuously. Often, the pathways can continue to transmit a pain signal after the injury has supposedly healed, or even when an injured site has been entirely removed (as in the case of phantom limb pain). Imprinting, a fairly recent concept, may serve as the explanation here. The nervous system gets "conditioned" to transmit certain pain messages. In other words, for some reason the pain gets "stamped" onto the pain pathways, inducing the cental nervous system to retain the memory of the pain for a while. The theory supposes that one way the nervous system gets stamped or stays turned on to the pain may be through a disruption in the balance of neurochemical transmitters relaying the pain mesages. As a result of the imprinting theory, researchers have become absorbed in spinal cord research for the treatment of both acute and chronic pain.

Pain starts with a physical event -- a cut, burn, tear or bump. Nerve endings, or pain receptors, in the periphery of your body (limbs and organs) pick up the pain. The receptors send the pain information from one bunch of nerve fibers to another to cells in the spinal cord, where the message is then relayed to the brain. This pathway is called the "ascending track".

This process can happen at different rates of speed because the nerve fibers that transmit the pain messages come in different sizes. Large diameter A-beta nerve fibers transmit pain quickly along the cable network. This is commonly known as "fast pain". You know it as the kind of pain that feels like "pressure". Two smaller diameter A-delta and C nerve fibers transmit pain information at a slower rate of speed. You know the A-delta pain as a "sharp" and "stabbing" pain you feel from a cut or burn. The C fiber pain is "dull and aching" and is typically called "slow pain" or secondary pain. As someone with chronic pain, you are all too familiar with C fiber slow pain -- the dull aching sensation usually associated with chronic problems.

The spinal cord is the central concourse along which all pain messages travel to and from the brain. When you stub your toe and your peripheral nerves register alarm, the pain is immediately relayed along the nerve fibers of your foot and leg to a special area within the dorsal horn of the spinal cord called the "substantia gelatinosa". The cells within the substantia gelatinosa relay this "fast pain" message along the pain tract, or the "neospinothalamic" pathway. The trip ends at specific locations in the brain, namely the "thalamus" and the "cortex". The cortex is the portion of the brain where most of your thought processes take place. A pain message arrives and the cortex prompts you to say "ouch!" and begin rubbing the afflicted area.

By contrast, chronic pain tends to move along a different, slower tract called the "paleospinothalamic" pathway. This "slow pain" tends to be dull, aching, burning, and cramping. Initially it travels the same route as the fast pain through the dorsal horn of the spinal cord. Once there, however, the slow pain message separates in the brain stem area to turn toward final destinations in a different portion of the brain, the "hypothalamus" and "limbic" structures. The hypothalamus is the gland responsible for instructing the pituitary gland to release certain stress hormones. It is sometimes referred to as the central clearinghouse of the brain. The limbic structures are the place where your emotions are processed. Their involvement in the process helps to explain how your feelings can influence your pain.