Physicians are not always able to alleviate the sources of pain and simply diagnosing what precisely is wrong physically with a person in pain can prove challenging. If there is an upside to the physical pain response and the body’s acute ability to perceive unpleasant sensations, it is not always easy to find.
The Pain Signal
The short answer as to why we, as humans (as well as other animals), have the ability to feel pain is that pain is a signal that something is wrong. Pain alerts us to bodily insults and injuries, which may be internal (such as a stomach ulcer or a twisted ankle) or external (such as a snakebite or getting too close to a fire). However, many ask why do we still feel pain, even if we aren’t in immediate danger or can’t do anything to change our situation? Our ancestors may have had to flee from predators, but in modern society, not many of us have to worry about avoiding a lion attack.
Evolutionarily speaking, we have evolved a pain response to help us get out of harm’s way, halt actions that may damage our bodies, and hopefully preserve our good health and our lives. Since these bodily insults may be life-threatening, our pain signals needed to evolve to be quite strong and hard to ignore in order to force us to quickly recognize and assess a situation and take immediate action as needed.
Fight or Flight
We know that pain signaling is closely linked to the so-called ‘Flight or Fight’ response—our body’s alarm system, which when activated, tells us to get out of harm’s way, or prepare to fight an immediate danger. More than just a mental state of awareness, this response is associated with important physical changes. Our hearts beat faster and breathing becomes more rapid, which enables our muscles to receive more blood flow and oxygen as we prepare to either run or fight.
What is really happening in the body when we feel pain is just beginning to be understood by medical science. We do know that the process begins when our cells or tissues emit a kind of ‘danger signal’, such as that stemming from inflammation or tissue damage. This bodily irritation causes chemicals called histamines to be released from our cells which can cause contractions in certain body parts, like the stomach or lungs. When nerve fibers in our bodies sense these chemicals, they send an electrical charge along the spinal cord to a region called the dorsal horn.
Pain Gate Signaling
The main pathway for pain signaling to our brains, the spinal chord can transmit pain signals arising from anywhere in our bodies. What happens at the dorsal horn is not fully understood, but this process of spinal pain signaling is often termed the "Pain Gate". Pain Gate signaling causes additional chemicals called neurotransmitters to be released, which convey the pain signal to our brains. Thus, neurotransmitters are the messengers which convey the urgent pain message to the brain.
Interestingly, there appears to be not just one, but many pain sensing centers in the brain, most likely because pain is such an important survival signal that the whole brain needs to be involved. In this light, it is not surprising that pain causes changes not only in how our brains process information, but also in our emotions and behavior.
As anyone can tell you, however, not all pain is created equal. There are at least two main categories of pain signaling, the first of which is very rapid (a kind of expressway for pain) while the second is slower (likened to a meandering side road). The former results in sharp, stabbing types of pain, while the latter leads to more continuous, dull pain. Of course our perception of pain can be a mixture of these two and may resolve rather quickly (acute pain) or linger (chronic pain). Generally, acute pain occurs when there is a rapid change in situation and something serious has happened to our bodies which may need to be resolved with quick action. For instance, we may feel the acute pain response if we trip and fall, scrapping a knee or breaking an arm. Chronic pain, on the other hand, is associated with longer-term conditions, such as an old injury or the wear and tear of aging.
