Gate control theory of pain The gate theory of pain was proposed in 1965 by Ronald Melzack and Charles Patrick. Not only did this theory revolutionize earlier pain research, it also significantly shaped the current understanding of pain transduction in the central nervous system. This theory recognized the experimental evidence that supported the specificity and pattern theories and provided a model that could explain these seemingly opposed findings. Drawing inspiration from different research models on pain, Melzack and Wall carefully re-examined the shortcoming of the dominant theories of the pain of the era. This re-examination was focused on bridging the gap between these theories with a framework based on the aspects of each theory that had been corroborated by physiological data. Specifically, Melzack and Wall accepted that there are nociceptors (pain fibers) and touch fibers and proposed that these fibers synapse in two different regions within the dorsal horn of the spinal cord: cells in the substantia gelatinosa and the “transmission” cells. The model proposed that signals produced in primary afferents from stimulation of the skin were transmitted spinal cord is the substantia gelatinosa in the dorsal horn, which modulates the transmission of sensory information from the primary afferent neurons to transmission cells in the spinal cord. This gating mechanism is controlled by the activity in the large and small fibers. Large-fiber activity inhibits (or closes) the gate, whereas small-fiber activity facilitates (or opens) the gate. Activity from descending fibers that originate in supraspinal regions and project to the dorsal horn could also modulate this gate. When nociceptive information reaches a threshold that exceeds the inhibition elicited, it “opens the gate” and activates pathways that lead to the experience of pain and its related behaviors. Therefore, the gate control theory of pain provided a neural basis for the findings that supported and helped to reconcile the apparent differences between the pattern and specificity theories of pain. INCIDENCE AND PREVALENCE OF PAIN IN THE GLOBAL POPULATION—A SYSTEMATIC REVIEW to three regions within the spinal cord (Campbell et al., 2020). These include: 1. Substantia gelatinosa. 2. Dorsal column. 3. Group of cells that they called transmission cells . According to Melzack and Wall’s proposal, the gate in the
Prevalence describes the proportion of the at-risk population affected by a condition. Population estimates for the prevalence of chronic pain vary widely according to case definition and ascertainment methods, time place, and population. Research suggests that chronic pain affects 13–50% of adults in the UK. Of those who live with chronic pain, 10.4–14.3% were found to have moderate to severe disabling chronic pain. Incidence is the number of new cases of a disease developing during a particular time in a population at risk of developing the disease. Although difficult to accurately determine because of a lack of longitudinal studies, the incidence of chronic pain in one region of the UK has been estimated at 8% per year (Denche-Zamorano et al., 2022). Chronic pain of moderate to severe intensity has been estimated to occur in 19% of adult Europeans, seriously affecting their daily activities and social and working lives. Most had not received pain specialist treatment and 40% reported inadequate management of their pain (Ghafouri et al., 2022). The World Health Organization has estimated that osteoarthritis affects nearly 10% of men and 18% of women aged >60 years; rheumatoid arthritis affects 0.3–1% of the general population and is more prevalent among women and in developed countries; and low back pain affects nearly everyone at some point in time and about 4–33% of the population at any given point (Veronese et al., 2022). However, the problem is not confined to adults, with an estimated prevalence of chronic pain in children and adolescents of 25% and with a third reporting the pain to be severe. In addition, the impact of chronic pain is expected to increase as the effects of population aging become apparent, and increased levels of obesity and lack of physical activity will increase the prevalence of conditions associated with chronic pain. As it appears, both the incidence and prevalence of pain in the global population at any point in time seem to depend on the interaction among multiple factors. Many of these factors are directly relevant to chronic pain predictions, assessments, management, and prognoses, and others will be important in the attempt to identify new targets for therapeutic intervention (Cruz et al., 2022). Factors popularly classified together in this regard include: Age While there is a paucity of evidence examining chronic pain in children and adolescents, the available literature suggests that older patients have a higher prevalence of chronic pain than younger groups of patients. Advanced age and chronic pain (and its reporting) have a complex interrelationship, whereby multi-morbidity is independently associated with chronic pain
(Hawker et al., 2021). With increasing age comes increasing multi-morbidity; the more advanced a patient’s age, the more they are likely to have experienced noxious stimuli or injury that can trigger chronic pain. For example, in people with shingles, those aged 50–54 years have an 8% chance of developing post-herpetic neuralgia, whereas those aged 80–84 years have a 21% chance of its development (Choi et al., 2021). Assessing pain in older patients can be complex, particularly because older adults are often reticent to discuss or disclose the level of their pain. Age-related disease processes, such as cognitive decline and dementia, can make identifying and managing chronic pain more difficult. Also, age-related disease processes, such as cognitive decline and dementia, can make identifying and managing chronic pain more difficult. Characteristics of pain, including duration and severity, area of the body affected, and the number of sites of pain, were found to be indicators for ongoing pain in older women, but these were less relevant in older men. Chronic pain is not limited to older age groups, however. A study from across 42 countries identified that self-reported chronic pain among adolescent populations was common: 20.6% of young people experienced pain in at least two sites of headache, stomach, and backache. Chronic pain affects up to 30% of those aged 18–39 years. Younger age seems to be a risk factor for chronic post- surgical pain. Gender According to the available body of evidence, men are reportedly less likely to report or experience chronic pain than women, and girls are more likely to report pain in multiple sites than boys (Lunde et al., 2022). Several reviews have studied how gender (role) and sex (biological) differences are related to the way men and women experience pain (Windgassen et al., 2022). An early systematic review submitted that women who experience pain are more likely to use maladaptive coping strategies, which predispose them to chronic pain and poorer functional ability. Women have been shown to have lower pain thresholds and tolerance and are more likely to experience greater intensity and unpleasantness with pain. The evidence also suggests that women have different sensitivities to analgesia. When corrections are made for the prevalence of pain in the different genders, women are more likely to seek treatment for their pain. Multiple pain-related clinical studies from specialist pain clinics have submitted a reporting rate of women that is twice the rate of men. Women also reportedly showed a higher level of pain intensity and higher pain-related disability than men. Although there is insufficient information on the mechanisms behind these sex-specific differences in pain perception and pain prevalence,
Book Code: PYFL4024
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