The International Association for the Study of Pain defines pain as \u201can unpleasant sensory and emotional experience that is associated with actual or potential tissue damage.\u201d It serves as the body\u2019s protective withdrawal<\/strong> mechanism<\/strong> or warning<\/strong> signal<\/strong> both from physical damage and to allow for healing to occur. Through a learned process, an individual may avoid similar situations in the future that may cause pain [R<\/a>].<\/p>\n Interestingly, the level of pain might not always correspond to injuries or tissue damage to the body [R<\/a>]. Many people have pain with no detectable injuries, while some people have a lot of physical damage with no pain.<\/p>\n Simple painkillers and pain relief medications for acute pain provide effective results 20 <\/strong>– 70%<\/strong> of the time. However, oral painkillers are not<\/strong> effective at reducing the duration of chronic pain<\/strong> [R<\/a>].<\/p>\n Identifying pain based on its location, duration<\/strong>, and intensity<\/strong> can point to the underlying causes as well as the most effective treatments [R<\/a>].<\/p>\n Acute pain<\/strong> is a normal response to harmful stimuli, injuries, or a disease. Typically, this pain resolves once the stimuli are removed, or the damaged tissue is healed or relatively soon thereafter [R<\/a>].<\/p>\n Acute pain stimuli also activate the fight-or-flight mechanisms and may cause muscle spasms [R<\/a>].<\/p>\n Acute pain is experienced immediately<\/strong> and can potentially last up to 3 months<\/strong>. Pain that lasts more than 3 months<\/strong> after the injury is categorized as chronic pain<\/strong> [R<\/a>].<\/p>\n Chronic pain is due to persistent activation<\/strong> of nociceptors <\/strong>(neurons that help transmit pain signals to the brain<\/strong>) in the areas around the damaged tissue. However, chronic pain may continue<\/strong> despite any identifiable triggers, damage, or injury.<\/p>\n Common chronic pain disorders include [R<\/a>]:<\/p>\n Abnormalities in the nervous system can result in lasting pain long after the original injuries have disappeared, as is the case of complex regional pain syndrome [R<\/a>]. Symptoms include swelling, changes in muscle tone, immobility, and reduction in blood flow to the affected area.<\/p>\n Independent of the cause, chronic pain results from a sustained sensory abnormality<\/strong> in the body.<\/p>\n Chronic pain is a result of many factors, including overall health<\/strong>, psychological factors<\/strong>, and hormones<\/strong> [R<\/a>].<\/p>\n Uncontrolled chronic pain can decrease<\/strong> immune function<\/strong>, promote tumor growth<\/strong>, and hinder the healing process<\/strong>, increasing the risk of disease (morbidity) [R<\/a>].<\/p>\n There are three<\/strong> types of physical pain with distinct mechanisms of action. Each type requires different treatments to relieve or eliminate it [R<\/a>].<\/p>\n Nociceptors<\/strong> are specialized pain-sensing receptors on the skin and limbs [R<\/a>]. Nociceptive pain<\/strong> is caused by extreme temperatures, pressure<\/strong>, or chemicals<\/strong> [R<\/a>].<\/p>\n While nociception<\/strong> is a sensation<\/strong>, the feeling of pain<\/strong> is a perception<\/strong>. If certain nerves or receptors are blocked, there will be nociception without pain [R<\/a>].<\/p>\n The signal created by the activation of nociceptors is proportional to the strength of the stimulus or degree of damage [R<\/a>].<\/p>\n When the stimulus intensity reaches a point called the noxious threshold<\/strong>, nociceptors are activated [R<\/a>].<\/p>\n The axons involved with nociception are relatively slow<\/strong> to conduct pain signals to the brain. These axons are typically lightly myelinated<\/strong> (insulated to increase action potential conduction and speed up nerve signals) or more commonly unmyelinated<\/strong> [R<\/a>].<\/p>\n These types of axons are present in the two<\/strong> major classes of pain neurons. The first class has medium-diameter and myelinated axons that transmit acute, well-localized fast pain<\/strong>. The second class of nociceptors is small unmyelinated \u201cC\u201d fibers that transmit poorly localized slow pain<\/strong> [R<\/a>]. The pain signal travels to the brain (cerebral cortex), where the signal is processed.<\/p>\n Although most nociceptors are located in the skin, some nociceptors are found in internal organs such as the heart, lungs, testes, and the digestive tract [R<\/a>].<\/p>\n In inflammatory pain, inflammatory proteins released by white blood cells<\/a> (IL-1\u03b2<\/a>, IL-6<\/a>, TNF-\u03b1<\/a>, IL-1<\/a>2<\/a>, IL-18<\/a>, IFN\u03b3<\/a>) activate the nociceptors, rather than damaging stimuli such as heat or pressure [R<\/a>, R<\/a>, R<\/a>].<\/p>\n In addition to these inflammatory proteins, the following substances also sensitize the nociceptors in the damaged tissue [R<\/a>]:<\/p>\n These substances expand<\/strong> blood vessels<\/strong> (vasodilation) and increase swelling in the damaged tissues [R<\/a>].<\/p>\n Inflammatory pain is meant to protect an injured body part and promote healing and rest [R<\/a>].<\/p>\n The skin, joints<\/strong>, and gut<\/strong> are susceptible to in\ufb02ammatory pain, which can appear as inflammation of the skin<\/strong> (such as atopic dermatitis), arthritis<\/strong>, and in\ufb02ammatory bowel disease<\/strong> [R<\/a>].<\/p>\n In pathological pain, inflammation in the brain<\/strong> causes brain dysfunction. Neurons and immune cells in the brain (astrocytes and microglia) communicate with each other through inflammatory signals, which drive pain perception [R<\/a>].<\/p>\n This leads to :<\/p>\n Unlike nociceptive and inflammatory pain, pathological has no protective purpose [R<\/a>, R<\/a>]. In addition, it does not travel along the traditional pain pathways [R<\/a>].<\/p>\nAcute vs. Chronic Pain<\/strong><\/span><\/h2>\n
\n
Mechanisms of Action for Physical Pain<\/span><\/h2>\n
1) Harmful Stimuli<\/strong><\/span><\/h3>\n
![\"\"](\"https:\/\/selfhacked.com\/app\/uploads\/2017\/09\/word-image-3-480x209.png\")
<\/p>\n2) Inflammation<\/strong><\/span><\/h3>\n
\n
3) Inflammation in the Brain (Pathological Pain)<\/strong><\/span><\/h3>\n
![\"\"](\"https:\/\/selfhacked.com\/app\/uploads\/2017\/09\/word-image-4-480x329.png\")
<\/p>\n\n
Causes of Pathological Pain<\/strong><\/h4>\n
\n