Page 110 Complete Your CE Test Online - Click Here Nociceptive pain and neuropathic pain There are two main subtypes of pain, nociceptive pain and neuropathic pain. Nociceptive pain is the perception of noxious stimuli usually caused by tissue damage. It can further be categorized into somatic or visceral pain (Rosenquist, 2017). Somatic pain occurs from tissue injury that occurs in the skin, as well as deep tissue—such as fascia, tendons, and bone—and can be described as sharp then burning or throbbing and is easily localized (Samcam & Papa, 2016). Visceral pain originates in the viscera, usually in internal organs, and is mediated by stretch receptors that allow a poorly localized, deep, and dull sensation (Rosenquist, 2017.) In the case of appendicitis, for example, the pain may be poorly localized and visceral in nature, but as the inflammation increases, the pain may become sharp and more localized to the right quadrant involving somatic nerves (Samcam & Papa, 2016). Neuropathic pain occurs as a result of abnormal neural activity resulting from injury, disease, or dysfunction of the nervous system. It includes such conditions as diabetic neuropathy, trigeminal neuralgia, and thalamic pain (Rosenquist, 2017). Approximately 50% of all diabetic patients experience neuropathy ( Institute for Clinical Systems Improvement [ICSI], 2005). Neuropathic pain can be constant or intermittent and include pain that is burning, shooting, crawling, numbing, itching, and tingling (Dworkin et al., 2003). Self-assessment question 1 A person stung by a bee will experience what type of pain? a. Neuropathic pain. b. Pathologic pain. c. Visceral pain. d. Nociceptive pain. Physiology of pain Nociception is a four-stage process that the body utilizes to process painful stimuli (Copstead & Banasik, 2013): 1. Transduction: Painful stimuli are converted to neuronal action potentials at the sensory receptor. 2. Transmission: Action potentials move via neurons from peripheral receptors to the spinal cord and then to the brain. 3. Perception: The brain receives the information from the action potentials and perceives them as painful. 4. Modulation: The process by which the transmission of pain is altered. Nursing consideration: It is important for the nurse to get as much information about the quality of pain the patient is experiencing. The description of pain (dull, sharp) can provide information useful in determining the underlying cause. For example, a patient with dull back pain that is poorly localized may be experiencing visceral pain caused by kidney inflammation. The patient experiencing sharp and localized back pain may have a musculoskeletal issue (Samcam & Papa, 2016). Transduction Painful stimuli are first encountered by nociceptors, which are nerve endings. Nociceptors convert painful stimuli into neuronal action potentials that travel through the spinal cord and finally to the brain. Nociceptors are located throughout the body in the skin; muscle; connective tissue; the circulatory system; and the viscera of the abdomen, pelvis, and thoracic cavity (Copstead & Banasik, 2013). Nociceptors can be stimulated by direct injury to the nerve endings themselves or they can be stimulated from the release of chemicals as a result of the injury as part of the inflammatory response. These chemicals include potassium, hydrogen, lactate, prostaglandins, serotonin, and bradykinin. These chemicals affect the membrane potential of the pain receptor and depolarize causing an action potential that makes its way to the brain and is processed by the brain as pain. Transmission A delta fibers and C fibers are primary afferent neurons that transmit action potentials (also known as nerve impulses) to the central nervous system. A delta fibers are larger and myelinated and quickly carry impulses (about 0.1 s) that result in sharp and stinging pain; C fibers are smaller and unmyelinated, taking longer (about 1 s or more) to transmit impulses and result in a dull, aching pain sensation (Copstead & Banasik, 2013; Guyton & Hall, 2006). A delta fibers are responsible for the initial sharp pain sensation a person feels, which causes the person to swiftly remove himself from the cause of injury (Guyton & Hall). C fibers relay a slower pain that grows greater over time and causes suffering (Guyton & Hall). Nociceptive impulses travel through A delta and C fibers and enter the spinal cord from the dorsal roots and then to synapse relay neurons at the dorsal horn (Guyton & Hall, 2006). The pain signals travel to the brain via the spinothalamic tract (Copstead & Banasik, 2013). The A delta pain fibers are mostly transmitted via a spinothalamic tract known as the neospinothalamic tract and secrete an instantaneously acting neurotransmitter known as glutamate (Guyton & Hall). The neospinothalamic tract has fewer synapses than the paleospinothalamic tract that the slower C fibers travel, and the information they carry is quickly transmitted to the thalamus and the primary somatosensory cortex (Copstead & Banasik). As a result of this quick transmission, pain is easily pinpointed. The slower C pain fibers take the paleospinothalamic pathway. It is believed that type C pain fibers secrete both glutamate and a slower acting neurotransmitter known as substance P, which is associated with the transmission of slow and chronic pain (Guyton & Hall, 2006). This pathway contains more synapses and goes to various parts of the brain but mostly end in the lower regions of the brain associated with chronic suffering pain (Copstead & Banasik, 2013; Guyton & Hall). As a result of the many synapses and slower transmission time, pain transmitted via the paleospinothalamic pathway is harder to localize, which may account for patients being unable to provide specific information about pain location. Self-assessment question 2 Which of the following statements is TRUE regarding nociceptive pain impulse conduction in the example of a person stung by a bee? a. The nociceptive pain impulse from the bee sting traveled via A delta fibers and caused the sharp, well-localized pain sensation. b. The nociceptive pain impulse from the bee sting traveled via C fibers resulting in a sharp, well-localized pain sensation. c. The nociceptive pain impulse traveled through A delta fibers via the paleospinothalamic tract. d. The nociceptive pain impulse traveled through C fibers via the neospinothalamic tract. Perception Pain perception is how the brain processes the information it receives from nociceptive impulses. Perception of pain is influenced by anxiety, fear, and prior experiences (Copstead & Banasik, 2013). Pain perception makes the pain experience unique to every individual. Pain threshold is the amount of painful stimulation needed to provoke the perception of pain and is similar in most people (Copstead & Banasik). Pain tolerance varies from person to person and is influenced by genetics, culture, gender, age, and previous experience with pain (Copstead & Banasik). Pain expression is how the pain is communicated—crying, grimacing, moaning (Copstead & Banasik).