The Causes and Affects Of Pain.
The primary purpose of pain is its function as a protective mechanism for the body. It is part of the body's warning system. Pain usually is an indication that tissues have been irritated or damaged. For example, you may have burned yourself or sprained your ankle. However, there are times that pain can arise when there is no apparent damage or injury to the body.
Pain is an amazingly complex subject. First off, pain is an unpleasant "sensation" that we experience. The "pain experience" occurs in a number of ways and has many aspects to it. These include such things as a person's anticipation of pain, pain expectation, previous pain experience, emotional and psychological factors, cultural differences, the individual's tolerances and capacity to deal with the pain, etc. Pain is very subjective and individually based. What one person may experience as moderate or even excruciating pain, another person may experience as a mild pain and discomfort. This is an extreme example, but I have been amazed at the individual differences and tolerances I have witnessed in patients in my practice. It is important to understand that pain is not always what appears on the surface.
To provide you with a basic understanding of pain, we must begin with a brief discussion of the pain pathways in our body. While this material may seem difficult to understand without a medical background, a basic understanding of how our body stimulates, derives and interprets pain is very important.
The pain pathways discussed below are only one physical aspect of the complex experience that we call pain. I have made every effort to take this established clinical knowledge and put it into understandable terms; however, some words and statements don't lend themselves to simple terms.
To understand the pain pathways, we must have a basic understanding of the nervous system and how it functions. According to Dorland's Medical Dictionary, the nervous system is "the organ system which, along with the endocrine system, correlates the adjustments and reactions of the organism to its internal and external environment, comprising the central and peripheral nervous systems." In simple terms, the nervous system provides most of the control functions for the body; including both sensory and motor functions, as it responds and reacts to the environment outside and inside of us. For the purposes of this book, we will focus on those portions of the nervous system that relate to the experience of pain.
To best describe how our bodies come to respond to a "pain" stimulus, we begin with the pain receptors. Pain receptors are specialized sensory nerve endings that responds to various stimuli (such as a burning candle) by responding with a pain signal. Think of a piece of thread (the free nerve ending/receptor) that is lying in the skin or within a muscle. These "receptors" are spread throughout our skin, organs, bone coverings, arterial walls, joint surfaces, muscles and ligaments, etc.
When something occurs, such as trauma or damage, a signal is relayed to these specialized receptors that is interpreted as a "pain stimulus." At this point, the pain stimulus is transmitted along specialized sensory nerves to the spinal cord and up to the brain, where the pain stimulus is processed and a response is provided back to the various structures which need to initiate an action (such as moving our hand away from the flame).
The following is an example of the pain response process. The following scenario will provide you with an understanding of this process: You are walking barefooted and step on a nail. The 'negative stimulus" is the nail penetrating the skin of your foot.
1. The "pain receptors" in the skin of your foot are activated by the penetrating nail. This stimulation is translated into a "pain signal" which travels through the afferent (sensory) pathway to the spinal cord.
2. Within the spinal cord, the pain signal is sent through more sensory tracts to the brain, which becomes aware and analyzes the pain stimulus.
3. The brain then sends an outgoing signal to various areas of the body which initiates a response. The head, neck, arms, trunk and opposite leg (causing muscular reactive movements), and the tongue, throat and respiration (gasp of pain or an exclamation), all may respond.
4. Further, a signal is sent back down the spinal cord and out the "efferent" (motor) pathway to the "effectors" (motor receptors in the muscles); in this case, to the muscles of the leg and foot which stepped on the nail.
5. The final reaction is the sharp withdrawal of the foot from the nail (the pain stimulus).
The response time in this entire scenario is instantaneous. It is interpreted by the body and reacted to so fast that we are already pulling our foot away from the nail before we actually have conscious recognition of what actually has occurred.
Pain receptors are located all over our body. Most of our deep tissues are not heavily supplied with these or other types of pain receptors; however, there are enough to create a pain stimulus. There are essentially three types of pain receptors: Mechanosensitive receptors, stimulated by mechanical stress or damage; Thermosensitive receptors, stimulated by heat or cold; and Chemosensitive receptors, stimulated by various chemical substances which are irritating. An example of each of these is as follows:
1. Mechanosensitive receptors: You suffer an ankle sprain while playing soccer. The mechanical stress and damage to the muscles, ligaments and ankle joint stimulates this type of receptor and you experience pain.
2. Thermosensitive receptors: You take a pan of boiling soup off the stove and accidentally brush your hand against the pan's surface; or after a night of freezing weather, you brush your hand up against a frozen pipe. In both cases, the sensitivity of these receptors to heat and cold will activate the pain response. You will experience pain and immediately withdraw your hand.
3. Chemosensitive receptors: You are cleaning your car battery and some of the acid gets on you hand. The acid will stimulate this type of receptor and you will experience pain.
As discussed previously, once the pain receptors have received a stimulus, they send a pain signal along the afferent (sensory) nerve pathway of pain fibers back to the spinal cord. There is an important aspect to this pain signal and the response of the pain fibers. The pain fibers contain two components: "Fast" pain fibers and "Slow' pain fibers. This is important because we end up with a double system of pain innervation; one which gives us a fast "pricking type" of pain and the other a slower, "burning" sensation of pain. The "pricking" pain tells us very quickly that damage may be occurring and thus we react to stop it. The "burning" pain tends to become more and more painful over time, is most apparent after tissue damage and tends to linger.
At the spinal cord, the pain stimulus enters the cord and travels along specified "sensory spinal tracts" to the brain. These spinal cord tracts are specific to the transfer of the pain signal and are very complex. An important consideration of these tracts is that the "intensity" of the pain sensation can be modified as it travels to the brain; either as a decreased or increased pain signal. The pain signal is eventually transmitted to the brain where it is received, interpreted and an appropriate response sent back to the body to initiate a specific action.
Please realize that the above explanation is a simplistic rendition of this incredibly complex system. The pain sensation and response is very involved and tends to integrate directly and indirectly, many other aspects of the nervous system. Our bodies have a magnificent network to provide us with pain sensations and a way to respond to them.
The pain sensation is as varied as it is complex. Pain can occur in one area, multiple areas, and radiate from one site to another. Pain is most often classified based on its duration and whether its source is somatic or visceral. Pain duration is described as:
* Acute (new, immediate or recent)
* Prolonged or subacute (lasting days to weeks)
* Chronic (ongoing, lasting months to years)
Acute pain is usually of a short time frame, tends to be protective in nature and is usually not associated with significant tissue damage. Prolonged pain is the most common form and is always associated with tissue injury and inflammation. Chronic pain typically is just the opposite of acute. It can be of unlimited duration, is usually not protective to the body, and can be associated with significant tissue damage. In some chronic pain cases, the damage may have been resolved but the pain syndrome continues. Chronic pain is defined as pain lasting longer than six months.
Pain can strike different body tissues and regions. Terms have been defined to identify particular structures. The term "somatic" relates to the skin, muscles, ligaments, joints, connective tissue, etc. It is characterized as being localized, meaning you can pinpoint the area from which the pain is coming from. An example of this type of pain would be from spraining the right ankle. When you sprain your right ankle, you know that you have hurt and damaged the right ankle.
Visceral pain, on the other hand, is diffuse (spread out) and difficult to localize. It can be from organs or deep lying, non-organ structures and can refer pain to the skin. An example would be pain from the gall bladder. That pain is spread across the right mid to low abdomen, and can refer pain to the low and mid back and down into the groin on the right side.
Pain can be described in many ways: Aching, throbbing, burning, deep, stabbing, dull, sharp, etc. Pain descriptions, to limit confusion, have been placed into three specific categories. They are:
* Pricking Pain is experienced when we stick ourselves with a sharp object or cut our skin.
* Burning Pain occurs when we burn our skin.
* Aching Pain is a deep type of pain that can vary from an annoyance to severe pain.
Pain descriptions are very important in identifying the pain syndrome. Different types of pain are experienced with different conditions. Establishing and learning your particular pain pattern is important in developing a treatment program specific to your needs.
So you now have an idea of how pain works and how it is categorized. But how do we feel and experience pain? As headaches, neck and back pain, joint pain, abdominal pain, menstrual pain, reproductive pain, pain from trauma and injury, organ pain (such as from the gallbladder or liver), disease pain (such as from cancer or arthritis), etc. Pain is such a common malady that we have labeled areas of the affected part of the body with a pain title that is descriptive to that part or area: Headaches, low back pain, etc. Pain is not particular, it can strike all parts of our bodies. What is important, is to learn and understand the causes of pain. With this knowledge, you and your health care professional can evaluate and treat not only the pain itself, but the underlying cause that has triggered the pain response.
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