A European Informational Website
learn more
Pain is an unpleasant sensation; nociception[1] or nociperception[2] is a measurable physiological event of a type usually associated with pain and agony and suffering. The word "pain" comes from the meaning punishment, a fine, a penalty. A sensation of pain can exist in the absence of nociception: it can occur in response to both external perceived events (for example, seeing something) or internal cognitive events (for example, the phantom limb pain of an amputee). Pain is defined as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” - International Association for the Study of Pain (IASP). Scientifically, pain (a subjective experience) is separate and distinct from nociception, the system which carries information, about inflammation, damage or near-damage in tissue, to the spinal cord and brain. Nociception frequently occurs without pain being felt and is below the level of consciousness. Despite it triggering pain and suffering, nociception is a critical component of the body's defense system. It is part of a rapid warning relay instructing the central nervous system to initiate motor neurons in order to minimize detected physical harm. Pain too is part of the body's defense system; it triggers mental problem solving strategies that seek to end the painful experience, and it promotes learning, making repetition of the painful situation less likely. The two most common forms of pain reported in the United States are headache and back pain.
Pain may range in intensity from slight through severe to agonizing. It is experienced as having qualities such as sharp, throbbing, dull, nauseating, burning and shooting. It often has both an emotional quality and a sensed bodily location. Medical professionals will sometimes ask patients to rate their pain on a scale of zero through ten, where ten is consistent with screaming and thrashing about.
This subjective reality of the localization of pain to an area of the body is the basis for speaking of pain receptor, neck pain, referred pain, cutaneous pain, as well as pain in my foot, kidney pain, or the painful uterine contractions occurring during childbirth. This common usage of pain is not entirely consistent with the scientists' model of pain being a subjective experience.
Inability to experience pain, as in the rare condition congenital insensitivity to pain or congenital analgesia, can cause various health problems.
Pain can be classified as acute or chronic. The distinction between acute and chronic pain is not based on its duration of sensation, but rather the nature of the pain itself. In general, physicians are more comfortable treating acute pain, which has as its source soft tissue damage, infection and/or inflammation. It can be modulated and removed by treating its cause and through combined strategies using analgesics to treat the pain and antibiotics to treat the infection. In general, while it is uncomfortable to experience, it is easy to treat; is distinguished by having a specific cause and purpose, and generally produces no persistent psychological reaction. Physicians are more likely to prescribe medications to treat acute pain, particularly in those situations when they are satisfied that they understand the pain's origin and believe the pain will be short in duration. This is why a patient might leave the hospital with two weeks' worth of adequate pain medicine, but the same medications may not be readily prescribed if the patient's pain lasts beyond an expected period of time. It is not the pain itself that is short in duration: it is the diagnosis of "acute pain" and the expectation that it will be short in nature that continues to confuse both the medical establishment and those who experience pain.
The primary distinction is this: acute pain serves to protect one after an injury. Chronic pain does not serve this or any other purpose. Acute pain is the symptom of pain. Chronic pain is the disease of pain.
American pain associations estimate that 40-80 million Americans live with chronic pain. At the same time, there are only 8,000 qualified pain management specialists. Many physicians faced with patients who live with chronic pain have had no professional training in pain management. It is not regularly taught in medical school, and even recent legislation in some states to ensure that physicians receive continuing education in pain medicine and end-of-life care do not guarantee proper training in pain. In many states, there remains no legislation ensuring that licensed physicians, even those who work in hospital emergency rooms, have any pain management training whatsoever.
Chronic pain has no time limit, often has no apparent cause and serves no apparent biological purpose. Chronic pain can trigger multiple psychological problems that confound both patient and health care provider, leading to feelings of helplessness and hopelessness. The most common causes of chronic pain include low-back pain, headache, recurrent facial pain, cancer pain, and arthritic pain. And sometimes chronic pain can have a psychosomatic or psychogenic cause.[3].
Published information on pain perpetuate myths that do a disservice to those who live with pain and many glossaries contradict one another. One of the best studies, while slightly outdating and not answering all questions about chronic pain, was written by Dr. T.J. Murray of Dalhousie University.[4]
Chronic pain was originally defined as pain that has lasted 6 months or longer. It is now defined as "the disease of pain." Its origin, duration, intensity, and specific symptoms vary. The one consistent fact of chronic pain is that, as a disease, it cannot be understood in the same terms as acute pain, and the failure to make this distinction (particularly in those who suffer chronic pain) has been and continues to be the cause of multi-dimensional suffering, depression, social isolation, and helplessness. The failure to recognize chronic pain as substantially different from acute pain cannot be blamed on the medical profession: it is a societal lapse.
Chronic pain, no matter how debilitating it is in one's life, continues to be considered by most insurance carriers as a 3-17% disability.
There have been some theories that not treating acute pain properly can lead to chronic pain.[5]
The experience of physiological pain can be grouped according to the source and related nociceptors (pain detecting neurons).
It should be noted that visceral pain sensation is often referred by the CNS to a dermatome region which may be far away from the originating organ. These correlate to the position of the organ in the embryo. Examples of this include the heart which originates in the neck, thus producing the classical pain and arm pain experienced during acute cardiac pain.
Nociception is the system which carries information about noxious stimuli, usually but not always associated with tissue damage, to the spinal cord and brain[7].
Nociception is also known as nociperception and physiological pain. Nociception is separate to, and distinct from, psychological pain.
All nociceptors are free nerve endings that have their cell bodies outside the spinal column in the dorsal root ganglion and are named based upon their appearance at their sensory ends. These sensory endings look like the branches of small bushes. There are mechanical, thermal, and chemical nociceptors. They are found in skin and on internal surfaces such as periosteum and joint surfaces. Deep internal surfaces are only weakly supplied with pain receptors and will propagate sensations of chronic, aching pain if tissue damage in these areas occurs.
Two main types of nociceptor fibres, Aδ and C fibres, mediate fast and slow pain respectively. Thinly myelinated type Aδ fibres, which transmit signals at rates of between 6 to 30 meters per second mediate fast pain. This type of pain is felt within a tenth of a second of application of the pain stimulus. It can be described as sharp, acute, pricking pain and includes mechanical and thermal pain. Slow pain, mediated by slower, unmyelinated ("bare") type C pain fibers that send signals at rates between 0.5 and 2 meters per second, is an aching, throbbing, burning pain. Chemical pain is an example of slow pain. Nociceptors do not adapt to stimulus. In some conditions, excitation of pain fibers becomes greater as the pain stimulus continues, leading to a condition called hyperalgesia.
There are 2 pathways for transmission of nociception in the central nervous system. These are the neospinothalamic tract (for fast pain) and the paleospinothalamic tract (for slow pain).
When the nociceptors are stimulated they transmit signals through sensory neurons in the spinal cord. These neurons release glutamate, a major exicitory neurotransmitter that relays signals from one neuron to another.
If the signals are sent to the reticular formation of brain stem, thalamus, then pain enters consciousness, but in a dull poorly localised manner. From the thalamus, the signal can travel to the somatosensory cortex in the cerebrum, when the pain is experienced as localised and having more specific qualities.
Feinstein and colleagues found that nociception could also, "activate generalized autonomic responses independently of the relay of pain to conscious levels" causing "pallor, sweating, bradycardia, a drop in blood pressure, subjective "faintness," nausea and syncope" [8].
The gate control theory of pain, proposed by Patrick Wall and Ron Melzack, postulates that nociception (pain) is "gated" by non-nociception stimuli such as vibration. Thus, rubbing a bumped knee seems to relieve pain by preventing its transmission to the brain. Pain is also "gated" by signals that descend from the brain to the spinal cord to suppress (and in other cases enhance) incoming nociception (pain) information.
The analgesia system is mediated by 3 major components : the periaquaductal grey matter (in the midbrain), the nucleus raphe magnus (in the medulla), and the nociception (pain) inhibitory neurons within the dorsal horns of the spinal cord, which act to inhibit nociception(pain)-transmitting neurons also located in the spinal dorsal horn.
The body has several different types of opioid receptors that are activated in response to the binding of the body's endorphins. These receptors, which exist in a variety of areas in the body, inhibit firing of neurons that would otherwise be stimulated to do so by nociceptors.
Pain may be experienced differently depending on phenotype. A study by Liem et al. suggests that redheads are more susceptible to thermal pain. [9]
Gene SCN9A has been identified as a major factor in the development of the pain-perception systems within the body. A rare genetic mutation in this area causes non-functional development of certain sodium channels in the nervous system, which prevents the brain from receiving messages of physical damage. People having this disorder are completely ignorant to pain, and can perform without pain any kinds of self mutilation or damage. In the families studied, this has ranged from biting of the person's own tongue leading to damage, through to street acts with knives, to death from injuries due to a failure to have learned limits on injury through experience of pain. The same gene also appears to mediate a form of hyper-sensitivity to pain, with other mutations seeming to be "at the root of paroxysmal extreme pain disorder" according to a 2006 report in Neurone. Various other forms of somatic sensitivity are unaffected. [8]
A recent survey by NCCAM (part of the NIH) found pain was the most common reason that people use complementary and alternative medicine (CAM). Among American adults who used CAM in 2002, 16.8% used CAM to treat back pain; 6.6% for neck pain; 4.9% for arthritis; 4.9% for joint pain; 3.1% for headache; and 2.4% used CAM to treat recurring pain. (Some survey respondents may have used CAM to treat more than one of these pain conditions.)
One such alternative, traditional Chinese medicine, views pain as a qi "blockage" equivalent to electrical resistance, or as "stagnation of blood" – theorized as dehydration inhibiting metabolism. Traditional Chinese treatments such as acupuncture are said to be more effective for nontraumatic pain than traumatic pain. Although these claims have not found broad scientific acceptance, research into both the mechanism and clinical efficacy of acupuncture supports that it can have a role in pain reduction for both humans and animals. Although the mechanism is not fully understood, it is likely that acupuncture stimulates the release of large quantities of endogenous opioids.[10] A 2004 NCCAM-funded study showed that acupuncture provides pain relief and improved function in patients with osteoarthritis of the knee, causing some managed care organizations to support acupuncture as adjunctive therapy for this purpose.[11] The NIH's 1997 Consensus Statement on Acupunture notes that research has been mixed, partly due to difficulties with designing clinical studies with the proper controls.[12]
Another common alternative treatment for chronic pain is use of nutritional supplements such as:
The concept of pain has played an important part in the study of philosophy, particularly in the philosophy of mind. The question of what pain actually consists in is still open since any evaluation is dependent upon what subject one approaches the question from. Identity theorists assert that the mental state of pain is completely identical with some physical state caused by various physiological causes. Functionalists consider pain to be defined completely by its causal role (ie in the role it has in bringing about various effects) and nothing else. Some theologians and other spiritual traditions have much to say about the nature of pain and its various spiritual consequences, especially its role in growth, understanding, compassion, and in providing an aspect of life to be overcome.
Despite its unpleasantness, pain is an important part of the existence of humans and other animals; in fact, it is vital to survival. Pain encourages an organism to disengage from the noxious stimulus associated with the pain. Preliminary pain can serve to indicate that an injury is imminent, such as the ache from a soon-to-be-broken bone. Pain may also promote the healing process, since most organisms will protect an injured region in order to avoid further pain. People born with congenital insensitivity to pain usually have short life spans, and suffer numerous ailments such as broken bones, bed sores, and chronic infection.
The study of pain has in recent years diverged into many different fields from pharmacology to psychology and neurobiology. It was even proposed that fruit flies may be used as an animal model for pharmacological pain research [10]. Pain is also of interest in the search for the neural correlates of consciousness, as pain has many subjective psychological aspects besides the physiological nociception.
Interestingly, the brain itself is devoid of nociceptive tissue, and hence cannot experience pain. Thus, a headache is not due to stimulation of pain fibers in the brain itself. Rather, the membrane surrounding the brain and spinal cord, called the dura mater, is innervated with pain receptors, and stimulation of these dural nociceptors (pain receptors) is thought to be involved to some extent in producing headache pain. Some evolutionary biologists have speculated that this lack of nociceptive tissue in the brain might be because any injury of sufficient magnitude to cause pain in the brain has a sufficiently high probability of being fatal that development of nociceptive tissue therein would have little to no survival benefit.
Chronic pain, in which the pain becomes pathological rather than beneficial, may be an exception to the idea that pain is helpful to survival, although some doctors believe that psychogenic chronic pain exists as a protective distraction to keep dangerous repressed emotions such as anger or rage unconscious.[15]. And it is not clear what the survival benefit of some extreme forms of pain (e.g. toothache) might be; and the intensity of some forms of pain (for example as a result of injury to fingernails or toenails) seem to be out of all proportion to any survival benefits.
Pain is defined as a subjective conscious experience. The presence or absence of pain even in another human is only verifiable by their report; "Pain is whatever the experiencing person says it is, and exists whenever he says it does."[16] It is not scientifically possible to prove whether an animal is in pain or not.
To determine if an animal is likely to be able to experience pain, two tests are used.
From these lines of questioning the following groups have been identified;
In veterinary science this uncertainty is overcome by assuming that if something would be painful for a human then it would be painful for an animal.[21] Where possible, analgesics are used preemptively if there is any likelihood of pain being caused to an animal.
Contents