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Pain is an Unpleasant Sensation . It is defined by the International Association For The Study Of Pain (IASP) as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”. Nociception IASP Pain Terminology (sometimes also called ''nociperception''''The American Heritage Stedman's Medical Dictionary'', 2nd Edition, Houghton Mifflin, 2004. Cited online at medical-dictionary.thefreedictionary.com .) is a measurable Physiological event of a type usually associated with pain. 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 can convey information without conscious awareness. Conversely, but less frequently, a sensation of pain can exist in the absence of nociception. Pain 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 nociceptive system transmits signals that usually trigger the sensation of pain, it is a critical component of the body's ability to react to damaging stimuli and it is part of a rapid-warning relay instructing the Central Nervous System to initiate reactions for minimizing Injury . DESCRIPTION Intensity 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. Localisation This subjective reality of the localisation 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 Contraction s'' occurring during Childbirth . This common usage of ''pain'' is not entirely consistent with the scientists' model of pain being a subjective experience. INSENSITIVITY TO PAIN Inability to experience pain, as in the rare condition Congenital Insensitivity To Pain or congenital analgesia, can cause various health problems. TYPES OF PAIN 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. Chronic 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 Room s, 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. Sometimes chronic pain can have a Psychosomatic or Psychogenic cause.Sarno, John E., MD, et. al., ''The Divided Mind: The Epidemic of Mindbody Disorders'' 2006 (ISBN 0-06-085178-3) 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.1 The experience of physiological pain can be grouped according to the source and related Nociceptor s (pain-detecting Neuron s).
SELECTED COMMON AND SERIOUS CAUSES OF PAIN BY REGION 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. Head and neck
Thorax
Abdomen
Back
Limbs
Joints
PHYSIOLOGY OF NOCICEPTION Pain refers to the subjective, unpleasant sensation that accompanies damage or near-damage to Tissue s, though it can also occur in the absence of such damage if the systems of nociception are not functioning properly. Nociception refers to the system that carries signals of damage and pain from the tissues; it is the physiological event that accompanies pain. "Assessing Pain and Distress: A Veterinary Behaviorist's Perspective by Kathryn Bayne" in "Definition of Pain and Distress and Reporting Requirements for Laboratory Animals: Proceedings of the Workshop Held June 22, 2000 (2000) Nociception is also known as ''nociperception'' or''physiological pain'' and is distinct from Psychological Pain . Nociceptors All nociceptors are Free Nerve Ending s 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. Nociceptors can detect mechanical, thermal, and chemical stimuli, and are found in the Skin and on internal surfaces such as the Periosteum or 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. 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 . Transmission of nociception to the central nervous system There are two ways for nociceptive information to reach the Central Nervous System , the neospinothalamic tract for 'fast pain' and the paleospinothalamic tract for 'slow pain'. Neospinothalamic tract Fast pain travels via type Aδ Fiber s to terminate on the Dorsal Horn of the spinal cord where they Synapse with the Dendrite s of the neospinothalamic tract. The Axon s of these neurons travel up the spine to the Brain and cross the midline through the Anterior White Commissure , passing upwards in the contralateral anterolateral columns. These fibres terminate on the Ventrobasal Complex of the thalamus and synapse with the dendrites of the Somatosensory Cortex . Fast pain is felt within a tenth of a second of application of the pain stimulus and is a sharp, acute, prickling pain felt in response to mechanical and thermal stimulation. It can be localised easily if Aδ fibres are stimulated together with tactile receptors. Paleospinothalamic tract Slow pain is transmitted via slower type C Fiber s to laminae II and III of the dorsal horns, together known as the Substantia Gelatinosa . Impulses are then transmitted to nerve fibers that terminate in lamina V, also in the dorsal horn, synapsing with neurons that join fibers from the fast pathway, crossing to the opposite side via the anterior white commissure, and traveling upwards through the anterolateral pathway. These neurons terminate throughout in the Brain Stem , with one tenth of fibres stopping in the Thalamus , and the rest stopping in the Medulla , Pons and Periaqueductal Grey of the Midbrain Tectum . Slow pain is stimulated by chemical stimulation, is poorly localized and is described as an aching, throbbing or burning pain. Effects in CNS When the nociceptors are stimulated they transmit signals through sensory neurons in the spinal cord. These neurons release the exicitory Neurotransmitter Glutamate at their Synapse s. If the signals are sent to the Reticular Formation and Thalamus , the sensation of pain enters Consciousness 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. Nociception can also cause generalized Autonomic Responses before or without reaching consciousness to cause Pallor , Diaphoresis , Bradycardia , Hypotension , Lightheadedness , Nausea and Fainting .cite seen at Feinstein B, J Langton, R Jameson, F Schiller. Experiments on pain referred from deep somatic tissues. J Bone Joint Surg 1954;36-A(5):981-97 retrieved 2007-01-06 Analgesia The body possesses an endogenous analgesia system, which can be supplemented with Analgesic Drugs to regulate nociception and pain. There is both an analgesia system in the central nervous system and peripheral receptors that decreases the grade in which pain reaches the higher brain areas. The perception of pain can be modified by the body according to Gate Control Theory Of Pain . Central The central analgesia system is mediated by 3 major components : the Periaquaductal Grey Matter , the Nucleus Raphe Magnus and the nociception inhibitory neurons within the Dorsal Horn s of the spinal cord, which act to inhibit nociception-transmitting neurons also located in the spinal dorsal horn. Peripheral The peripheral regulation consists of several different types of Opioid Receptor s that are activated in response to the binding of the body's Endorphin s. 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. Factors See Also: Gate control theory of pain 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. PHENOTYPE AND PAIN Pain may be experienced differently depending on phenotype. A study by Liem ''et al.'' suggests that redheads are more susceptible to thermal pain.Liem EB, Joiner TV, Tsueda K, Sessler DI. Increased sensitivity to thermal pain and reduced subcutaneous lidocaine efficacy in redheads. ''Anesthesiology.'' 2005 Mar;102(3):509-14. 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 Channel s 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.http://www.nature.com/news/2006/061211/full/061211-11.html PAIN AND ALTERNATIVE MEDICINE A recent survey by NCCAM (part of the NIH ) found pain was the most common reason that people use Alternative Medicine . 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, 's 1997 Consensus Statement on Acupunture notes that research has been mixed, partly due to difficulties with designing clinical studies with the proper controls.National Institutes of Health Consensus Panel. "Acupuncture: National Institutes of Health Consensus Development Statement." National Institutes of Health Web site. Accessed at consensus.nih.gov/1997/1997Acupuncture107html.htm on February 24, 2007. Another common alternative treatment for chronic pain is use of nutritional supplements such as:
The efficacy of Glucosamine and Chondroitin, popular supplements for patients with arthritis, were examinied in the GAIT study, a $12 million trial funded by the NIH which showed statistical evidence for the treatment's positive effect only amongst patients with moderate to severe pain, a small subsection of the study.Clegg DO, Reda DJ, Harris CL, Klein MA, O'Dell JR, Hooper MM, Bradley JD, Bingham CO, Weisman MH, Jackson CG, Lane NE, Cush JJ, Moreland LW, Schumacher HR, Oddis CV, Wolfe F, Molitor JA, Yocum DE, Schnitzer TJ, Furst DE, Sawitzke AD, Shi H, Brandt KD, Moskowitz RW, Williams HJ. "Glucosamine, chondroitin sulfate, and the two in combination for painful knee osteoarthritis." ''New England Journal of Medicine''. 2006 Feb 23; 354(8): 795-808. PHILOSOPHY OF PAIN See Also: Pain (philosophy) 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. SURVIVAL BENEFIT 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 Sore s, 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.http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15763072&query_hl=21 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 Evolution ary 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.Sarno, John E., MD, et. al., ''The Divided Mind: The Epidemic of Mindbody Disorders'' 2006 (ISBN 0-06-085178-3) pp.61-65. 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 AND NOCICEPTION IN OTHER SPECIES 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."cite sourced from McCaffery M. Nursing management of the patient in pain. Philadelphia, Pa: JB Lippincott 1972. Currently, 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. American College of Veterinary Anesthesiologists' position paper on the treatment of pain in animals retrieved 2007-01-06 Where possible, analgesics are used preemptively if there is any likelihood of pain being caused to an animal. SEE ALSO
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