Pain remains one of the most remarkable systems of the body. While it enables us to learn about those things that might be dangerous to us, it can also trap a person within the confines of their own body. We will be discussing the physiology and psychology of this system, in a hope to empower those who might be suffering from chronic pain to take more control of their lives.
Physiology of Pain
The human body has specific receptors throughout the body, designed to carry information to warn when the body is approaching areas of damage. These receptors are called nociceptors, as they code for noxious information.
There are three primary types of sensory information that can produce pain—pressure, heat and cold, and chemicals. Clearly, any of these stimuli in excess can produce tissue damage. More than that, nociceptors can learn. If a pain receptor is stimulated, the amount of stimuli that are required to get the cell to fire will lower, making it more sensitive. Anyone who has had an injury, even a simply bruise, can attest that even a light touch can be painful in the area of the injury. In other words, the threshold of the nociceptor is lowered.
There are two primary types of nociceptors, and if you have pain, it is important to understand how these work. First, the most common type of nociceptor is the C fiber, which produces dull, aching pain. C fibers respond to many different kinds of stimuli, but most commonly respond to either pressure or temperature. While C fibers can respond to noxious chemicals, in general, A fibers respond to those, and produce an intense, sharp pain. . Why is this important? The primary chemicals that A fibers respond to are chemicals that are located within cells. This means that if you have sharp, intense pain, it tends to indicate that you already have tissue damage.
The lesson to take away from this is that while you can ignore dull, aching pain, in general, sharp, intense pain should be paid attention to. Anyone who has been active in athletics knows quite well that many things can hurt, particularly dull, aching pain, that are not necessarily really bad things. But when you have sharp, stinging, intense pain, you should stop whatever you are doing and pay attention to it. But there are other things that the physiology of pain can teach us about how to deal with the pain experience.
One of the really interesting parts of the pain systems deal with how fast these different fibers transmit their pain information. C fibers, as they can respond to a lot of different kinds of stimuli that can be present without tissue damage, are much slower—about 1-3 m/s. Most people have experienced this, when after you stub a toe, you don’t feel pain immediately, but it takes about 2-3 seconds to reach your attention. A fibers, as they respond primarily to chemical inside cells which are only present after tissue damage, have speeds up to 100 m/s.
One of the most important things to be aware of regarding this intricate system is that the system is designed to send signals BEFORE the situation approaches tissue damaging range. In other words, you can feel pain when nothing is actually damaged. This makes sense, in that the system is designed to be an early warning system - it only buys you so much if you get pain signals, only when something bad has already happened. Evolutionarily speaking, the system works much better if it can provide a warning before tissue damage occurs, in other words to allow you avoid the damage before it happens.
This can be very problematic for a patient who has pain. The most common reaction to pain is to stop whatever you are doing, that is eliciting the pain. While this is logical, it is not always a productive strategy in dealing with pain. One of the worst things a pain patient can do is to completely limit their activities. First, activity in itself, particularly cardiovascular activity, releases pain mediating chemicals. These chemicals, called endorphins, are thousands of times more powerful than morphine. Second, if you are completely sedentary, stopping all activity, this can make your injury worse. While stopping activity is very effective in the short term, in the long term this can lead to muscular degeneration, which can make dealing with the pain much more difficult.
The classic example of this is low back pain. There are a multitude of reasons that can result in low back pain. While most people think of injury, unfortunately as we age, the strength of bones and tendons can be severely impaired. All of the nerves that we use to sense our outside world exit the spinal cord from very small apertures - if a person has a loss of height in the vertebrae, or the building blocks of the spine, these exiting nerves can be compressed, and can cause tremendous pain. Similarly there are other non-spinal nerves that also travel through very small holes, like the sciatic nerve, with travels through the hips down into the legs. A very small muscle, called the pisiform, can become deconditioned, and can press directly on the sciatic nerve, and can cause tremendous pain.
Similarly, the muscles that support the spine can become deconditioned, specifically the abdominal wall and the erector spinae, or the low back muscles, and can lead to tremendous pain. Particularly in people who are overweight or obese, the muscles that support the back and spine are not able to provide adequate structural support, which can result in debilitating pain.
If you have lower back pain, and your spine films and CT scans are normal, before you turn to intense pain medications or shots, one of the first things you should try are exercises to strengthen the abdominal muscles and the lower back.