Pain Physiology

definition of pain

An ______ associated with actual or potential ______
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definition of pain

An ______ associated with actual or potential ______
unpleasant sensation and emotional experience

tissue damage
classification of pain
-nociceptive
-non-nociceptive

(depends on presence of tissue injury)
nociceptive pain
consequence of tissue injury

site of injury and surrounding area is source of pain--> normal/physiologic pain

associated with inflammatory response to heal damaged tissue

pain usually disappears unless there is irreversible damage to the tissue
nociceptive pain types
somatic pain

visceral pain
nociceptive pain: somatic pain
superficial and deep somatic pain
superficial somatic pain
cutaneous pain
deep somatic pain
musculoskeletal pain
nociceptive pain: visceral pain
neurovascular pain
non-nociceptive pain
neuropathic pain
non-nociceptive pain: neuropathic pain
episodic and continuous pain
physiological painnormal/good pain Early warning detection system: warns the organism of a tissue damaging stimulus in the environment. Initiated by tissue damage and inflammation (aka nociceptive/inflammatory pain) If pain is controlled --> healing process occurs and the nociceptive pain will stoppathological painBad/pathophysiologic pain Due to functional problem within the nervous system and may not be related to any peripheral tissue damage. ie: neuropathic pain, persists long after healing occurs noxious stimulus--> tissue injury --> inflammatory process associated with pain --> healing process --> but the pain continuesmechanism of nociceptive paintransduction transmission modulation perceptiontransductionThe process where a noxious stimulus is converted to electrical activity (nerve impulse) in the appropriate nerve ending Substances produced by nociceptors influence this processtransduction Substances produced by nociceptors influence this processbradykinin nerve growth factor prostaglandinstransmissionThe process of transmitting the nerve impulse to the cerebral cortextransmission impulse is transmitted through ____nerve fiberstransmission can be divided into 3 major stages:1) transmission of the nerve impulse from the site of transduction to the terminus in the trigeminal brain stem complex (in dorsal horn of spinal cord) 2) neuronal relay from the trigeminal brain stem complex to other brain stem areas and the thalamus 3) the reciprocal connection between the thalamus and the cerebral cortexnerve fibersheat cold mechanicalnerve fibers heatC fibersnerve fibers heat: C fiberssmall, unmyelinatedC polymodal nociceptors are called polymodal because they respond to ___________ stimulichemical stimuli or intense thermal and mechanical stimuliC polymodal nociceptors conduction velocity<2.5 m/sec slow2 major groups of C fibersone contains neuropeptides and the other group has no neuropeptides involved in the transmission of nociceptive impulsesnerve fibers cold:A deltanerve fibers cold: A deltasmall, lightly myelinatedA delta nociceptors will respond to ____________ stimulation and will conduct in the approximate range of _______m/secmechanical and thermal 2.5-252 types of A-delta nociceptive primary afferentsthe high threshold mechnoreceptors (responding to intense mechanical stimulation, ie: pinching) mechanothermal receptors (activated by either intense heat or a strong mechanical stimuli)nerve fibers: mechanicalA betanerve fibers: mechanical: A betalarge, thickly myelinatedmodulationProcess concerned with modifying neural activity leading to control over the pain transmission neurons.modulation can result ininhibition reduction enhancementperceptionThe subjective response of suffering and pain behavior that results when pain information is received in the higher centers of the brainnormal pain processing Ex of nociceptive pain: Man popped his wristnociceptive stimulus is converted into a nerve signal/action potential Once the noxious stimulus has been transducted, It is transmitted from the peripheral to the CNS along the axons of the nociceptors So the primary nociceptors (sensory nerve fibers) will synapse with second order neurons in the dorsal horn of the spinal cord and from there they will project to the brain stem and the thalamus Then when the pain signals the spinal cord and the brain, they can be modulated by the CNS (inhibited or enhanced) If the pain signals the cerebral cortex and limbic system, then the pain will be perceived as a different experience (influenced by social and environmental cues, cultural conditioning, and past personal experiences)nociceptive pain: acute pain can be triggered bydifferent stimuli including pressure, thermal energy, chemical irritation, chemicalspain theoriesspecificity theory the intensive or summation theory the pattern theory gate control theoryspecificity theoryA noxious stimulus evokes a sensation (pain) Similar to vision and touch Hardwired lines from specific "pain receptors" to CNS process pain related signalsthe intensive or summation theoryNoxious stimuli activates several types of receptors Summation of signals in CNS leads to painthe pattern theoryPattern of signals by noxious stimuli would be important for the recognition of pain / it's distinction from other sensationsgate control theoryProposes that there is a large amount of interactions between nociceptive and non-nociceptive input to the CNS there are nociceptive pain fibers and touch fibers which synapse in 2 different regions within the dorsal horn of the spinal cord-cells in the substantia gelatinosa (SG) and the transmission cells (T cells) proposed that the gate in the spinal cord was the substantia gelatinosa 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 -small fiber activity facilitates or opens the gate Proposed the activity could also modulate the gates so when we have nociceptive info reaching a threshold that exceeds the inhibition, it opens the gate and activates the pathways that lead to the experience of pain and its related behaviors ie: why rubbing an acutely injured body part can often at least temporarily produce some pain reliefacute painProtective mechanism Stimulus induced pain Accompanies tissue damage, inflammationchronic painLasts longer than a month following the healing of a tissue injury Lasts longer than 3 months May spread beyond the original injury areaacute pain: -cause -length -symptoms -responds to meds? -type of tissue?chronic pain: -cause -length -symptoms -responds to meds? -type of tissue?chronic pain conditionsJoint diseases (Low) back pain Headaches Cancer pain Post herpetic Diabetic neuropathy TMD's Phantom painfrom acute to chronicperipheral sensitization central sensitization altered pain modulationsensitization definitionA reduction in the threshold of nociceptive afferent receptors caused by local changes in the sensitivity of sensory fibers initiated by tissue damage (incr of nociceptor sensitivity to stimulation--> lowering of excitation threshold)peripheral sensitizationsensitization at the site of injury due to lower threshold for depolarization consequence= primary hyperalgesia/high inflammatory hyperalgesia (caused by release of chemicals causing pain in area damaged by noxious stimuli) defense mechanism (provides signal to immobilize the injured part)peripheral sensitization mechanismsTissue Damage Inflammatory Mediators Nerve Damage. Neuroma Transduction proteins Ion channels (Spontaneous) Neural Activitynerve injuryThe process of neurogenic inflammation will be playing a primary role in peripheral sensitization Neurogenic inflammation could be a consequence of either nerve damage (either by transection, compression by a tumor, or damage)inflammatory soupPeripheral or nociceptors sensitization is induced by chemical secretion following tissue damage and inflammationinflammatory soup: 2 prominent mediators of pain released from nerve cell bodies:neuropeptides: -substance P -calcitonin gene related peptide(CGRP)inflammatory soup players involvedtissue injury immune cells sympathetic nerves vascular secretion afferent fibersinflammatory soup players involved: tissue injurykinins 5HT histamine free radicalsinflammatory soup players involved: immune cellscytokines endorphines enkephalinesinflammatory soup players involved: sympathetic nervesNPY excitatory amino acidsinflammatory soup players involved: vascular secretionEAA NOinflammatory soup players involved: afferent fibersneurotrophines as NGF neuropeptides as substance P and calcitonin gene related peptidecentral sensitizationIncrease in the excitability of neurons within the central nervous system, so that normal inputs begin to produce abnormal responses. Although the pain feels as if it originates in the periphery, it is actually a manifestation of abnormal sensory processing within the central nervous systemanalgesiaabsense of pain in response to stimulation that would normally be painfulallodyniapain due to a stimulus that does not normally provoke painallodynia ie:tapping a sunburnt person on the back (typically doesn't hurt but in this case it does)hypoalgesiadiminished pain in response to a normally painful stimulus (caused by administration of analgesics)hyperalgesiaan increased response to a stimulus that is normally painful -primary and secondaryprimary hyperalgesiadamaged tissue (peripheral sensitization has occurred)secondary hyperalgesiasurrounding undamaged tissue (central sensitization has occurred)dysesthesiaAn unpleasant abnormal sensation, whether spontaneous or evoked that is not painfulorofacial pain Specialty of dentistry that encompasses the ______of pain disorders of the _____ and associated regionsdiagnosis, management and treatment jaw, mouth, faceorofacial pain pain associated with the __________ tissues of the _______hard and soft head, face, and neckorofacial pain tissuesskin blood vessels teeth glands musclesorofacial pain types based on tissue of sourcemusculoskeletal pain neuropathic pain neurovascular painmusculoskeletal painmasticatory muscle disorders TMJ disordersneuropathic paintrigeminal neuralgia atypical odontalgianeurovascular painmigraines headachesorofacial pain stepsassessment diagnosis differential diagnosis