Pain Management

In the last issue of InMotion there was an article introducing our discussion of post-amputation pain. In this current article we will examine the ways in which the pain that we experience is actually "felt" by each of us. In order to understand pain, we need to examine an incredibly complex subject known as neurophysiology. I will try to keep the discussion basic so that it is easy to understand.

You need to know that, despite intense research in this area, there is still very much that is not known or understood about human neurophysiology. We will build from those areas that are understood and try to make some logical guesses about what is not truly known. We will use some comparisons or analogies that may help us think about what is happening but they may not be truly scientifically accurate. The goal is for you to be able to think clearly and ask good questions about this vitally important area of post amputation rehabilitation.

Sensory Cortex of the Brain

"The pain is in your head." This true statement has

probably angered more people than any other. It is scientifically true that we all feel pain by using our brains. If our brain is not working and we are not aware, we do not feel pain. The misunderstanding arises when people think that "in your head" means imaginary.

Pain is actually felt in the sensory cortex of the brain.

The sensory cortex receives messages from the rest of the nervous system and organizes them into a pattern that the body can experience, either feeling them, seeing them, tasting them, smelling them or hearing them. The sensory cortex acts much like a television set, which picks up information, organizes it, and then displays it so that it can be understood. Without the television set, the information on the cable or in the air cannot be experienced in any useful way. You can think of the sensory cortex as the television screen.

The sensory part of the brain is far more complex than a simple television set. It is much more like a television studio control booth with many television monitors, each concentrating on the input from a different camera. Only our brain has millions of incoming cameras which we can concentrate on, but not all at once. Our attention can only be concentrated on a few things at one time, much like the television director choosing the view of one camera to send out to our homes.

The sensory nerves

As a part of the nervous system, the sensory nerves pick up information from their environment. They sense pain, heat, cold, touch, sound, vision and other things. The nerves themselves are very specific. A temperature nerve cannot experience pain. A touch nerve cannot experience sight. These sensory nerves are much like television cameras, microphones, and thermometers. Each provide information based upon what they sense in the environment. The thermometer measures temperature but cannot hear noises, etc.

Pain nerves are among the most primitive nerves we have. They experience pain when something harmful or disruptive happens to part of our bodies. They may feel being burned but cannot tell if the burn is from chemicals, heat, cold, or friction. They can feel being cut but cannot tell if it is a knife or a needle. They are not nearly as fast as some nerves, and they cover a fairly wide area so that it may actually be hard to be sure exactly where the pain originates.

Nerve transmission and neural circuits

The sensory nerves pick up the information from the environment but they must have the sensory cortex to interpret what they sense and they must also have the incredibly complex nervous system to connect them together and transmit the messages. The nervous system is like the connecting cables, television station, transmission towers, cable facilities, and antenna in your television system. Each of the components has its own role to play. If any one of them is abnormal the outcome may be flawed or even absent.

There are many points where bad information can enter the system, just as there are many places where your television image can be messed up. What your sensory cortex actually feels for you is a combination of all the things that happen from the nerve ending in the skin, muscle, bone or other tissue, through all the connecting nerves, all the way to the sensory cortex.

Just as there are many complex circuits between the camera and television screen, there are incredibly complex neuro circuits between the sensory nerve fiber and the sensory cortex. These complex circuits help control what you feel and help you make use of the information that you receive.

Nerves conduct information much like television cables transmit images. It is done by a series of electrical discharges along the nerve fibers. When the sensory nerve is stimulated by something like a pin-prick, the nerve cell becomes excited and sends an electrical message down its long fiber (called an axon) toward the spinal cord. The nerve axon from your toe runs all the way to the spine, where it connects with other nerve fibers. When the electrical signal gets to the end of the nerve axon, the impulse is transmitted to the next nerve by release of neurotransmitter substances like acetylcholine. The acetylcholine stimulates the next nerve, which acts like a relay runner and picks up the message can carries it along the spinal nerve tracts toward the brain.

The simple transmission of the nerve messages gets much more complicated in the spinal cord and brain because, there, they are affected by other types of nerves which can either make passage of the messages easier (facilitation) or harder (inhibition). They are also affected by a number of chemicals like narcotics, sedatives, muscle relaxers, anti-seizure drugs, local and general anesthetic agents, and many others. All these chemicals in some way influence nerve transmission. Some of the actions we understand quite well. Some of them we understand poorly. Many affect some people more than others and therefore are somewhat unpredictable from one person to the next.

Unfortunately, sometimes the nerves begin to excite themselves, much like when a public address system gets feed back from the speaker to the microphone and begins to squawk. This sometimes occurs when the nerve does not have something productive to do such as when an amputation has removed the real input from the nerve and it is lacking a real task. If something does not turn down the volume, the sensation can become terrible just like the terrible squawk from a speaker system. Medications and other techniques can help turn down the volume in a variety of ways. That will be an important part of our discussions regarding post operative pain in future articles.

Fortunately, there are built in nerve circuits and actions which can help turn down the intensity of sensations. This occurs naturally to all of us. You have certainly experienced smelling an unpleasant odor when you entered a room but then forgotten about it as you became used to it. This was because your brain directed your conscious attention away from the smell. Even if the smell did not go away, you might not think about it again until someone entering the room called it to your attention. Our brains can do this with painful impulses also, such as when you have a burn, a bruise, a cut, etc. The sensation of pain may become less even though the original injury has by no means healed.

There are some psychological techniques, such as meditation, relaxation, and other attention-directing activities, that can help diminish pain, or at least our attention to it. As was stated earlier, various medications can also play a role in diminishing perception of pain by the sensory cortex of the brain. There are other events, such as stress, anger, fatigue, and anxiety, which can enhance the feelings of pain and make them more bothersome. Many of the techniques we will discuss later work by facilitating or inhibiting various types of nerve transmissions.

Amputation and the sensory nerve circuit

When an amputation occurs, the nerve trunks are cut at the site of the amputation and the sensory nerve cells die and are discarded along with the amputated limb. This is the equivalent of the television transmission lines being cut and the camera being destroyed. The television screen, antenna, cable hook-up and television station may still be present and working. They are just no longer getting a valid input from that particular remote television unit. Since the sensory cortex of the brain, and the spinal cord, as well as all the intermediate connections, are still working, signals still come to the sensory cortex, even if they are not valid, real signals. Some of the signals are like static, some are from other neural circuits, and some of it we have no real idea about. The fact remains-the person still can feel the limb that is no longer present because the part of the brain that does the feeling is still alive and well.

The cut nerve can generate sensations of its own. Any sensation that could be experienced by the nerve prior to injury can still be perceived by the brain, even if the limb is no longer present. If the cut end of the nerve is squeezed or pinched, the nerve may be highly stimulated and send strong signals that appear to originate in the amputated part because this is where the nerve cell originally was located. Sometimes the feelings are electric tingling, like when the funny bone at the elbow is struck and electricity runs into the little finger. Other times the sensation is a deep, slow, burning pain.

Anything that the limb could have actually experienced when it was intact can still be experienced by the cut nerve and sensory cortex that is attached to it. Sometimes the experience may seem more intense because the sensory cortex is bored by having nothing to do and may seem to make a lot out of a little.

Conclusion

There are many important understandings which can come from the fairly simple neuroanatomy and neurophysiology which has just been discussed. Much of how pain phenomena occur following an amputation can be explained by understanding what has happened to these systems and how it might make them behave. It is important to understand these basics so that we can make some sense from the information which will be discussed in future articles in this series. Understanding how we feel pain can help us understand the methods of relieving that pain.

Editors note-

I have received several requests for information and advice following the first article. Post-amputation pain problems are tragically common and that is precisely the reason that we are devoting space and time to doing this series of articles. Unfortunately, there is no way that I can answer individual questions. When I invited questions and comments, I tried to make it clear that the questions would be used to direct the future articles. That I will definitely try to do.

There is no safe and valid way that I can attempt to answer individual questions or solve individual problems. If you have a problem that demands a quick, complete answer, please contact a comprehensive pain management program near you. If you do not know of one, you can ask your personal physician, the anesthesia or neurology department at a hospital or medical center near you, or contact your local medical society. Direct help for specific problems must be done on a personal basis.

With these conditions restated, I will appreciate your questions and ideas to be incorporated into future articles. Send them to Editor, InMotion Magazine, 900 E. Hill Avenue, Suite 205, Knoxville, TN 37915 or e-mail to ACAEdward@aol.com  .