Presentation on theme: "﴿و ما أوتيتم من العلم إلا قليلا﴾"— Presentation transcript:
1 ﴿و ما أوتيتم من العلم إلا قليلا﴾ بسم الله الرحمن الرحيم﴿و ما أوتيتم من العلم إلا قليلا﴾صدق الله العظيم الاسراء اية 58
2 Assist Prof. of Medical Physiology Physiology of Pain andPain Control SystemByDr. Abdel Aziz M. HusseinAssist Prof. of Medical Physiology
3 Pain SensationDef :Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damageSignificance:Pain is a warning signal for tissue damage. It is the prominent symptom of tissue damagePain has a protective function. It initiates protective reflexes that;Get rid of the painful stimulus.Minimize tissue injury or damage.
6 Occurs at the time of injury Pain SensationA) According to its duration:Pain is classified into 2 types;1. AcuteFast or epicritcOccurs at the time of injury2. ChronicSlow or protopathicAfter injury
7 Pain Sensation Cutaneous pain Deep pain Visceral pain B) According to site of origin: 3 types;Cutaneous painFrom skin and subcutaneous tissuesUsually pricking or burning painDeep painFrom structures deep to the skin e.g. skeletal ms, joints, and tendonsUsually dull aching or throbbingVisceral painFrom internal viscera e.g. stomachUsually colicky or dull aching
8 Pain Sensation 1. Physiological Pain 2. Pathological Pain C) According to its mechanism or cause:Pain is classified into 2 main types;1. Physiological PainAlso called Nociceptive painCaused by stimulation of pain receptors by tissues damage e.g. in inflammation2. Pathological PainAlso called neuropathic painCaused by damage of nerve pathway e.g. sciatica
11 Pain Receptors 1) Morphology: are specific free nerve endings Pain Rs are morphologically similar but functionally they are specific1) Morphology: are specific free nerve endings2) Highly specific i.e. respond to tissue damage onlyClassified according to their adequate stimulus into:-a) Mechanical Pain Rs:Respond to strong mechanical trauma e.g. cuttingb) Thermosensitive pain Rs:Respond to excessive changes in temp (above 45°C and below 10°C).c) Chemical Pain Rs: respond to noxious chemical stimuli.d) Polymodal Pain Rs: respond to a combination of mechanical, thermal, and chemical noxious stimuli
12 Pain Receptors 3) Distribution: Abundant in the skin and some internal tissue such as the periosteum, arterial wall, joint surfaces, and the dura of the tentorium cerebelli.Few in deep tissues and all viscera. So, for pain to occur, painful stimulus must by intense and widespread. The deep & visceral pain is poorly localized.Brain itself and the parenchymal tissues of the liver, kidneys, and lungs have no pain receptors “pain insensitive structures”
13 Pain Receptors 4) Threshold : It is the lowest intensity of injurious agent needed to stimulate the pain receptors to cause pain sensationPain receptors are of high threshold: the pain receptors needs sufficient degree of tissue damage to be stimulated.Measured by;By pricking the skin with a pin at measured levels.By compressing the skin against hard objects.Thermal method (more accurate) (45 C)
14 Pain Receptors 5) Adaptation: Slowly adapting receptors even non adapting receptorsThis is very important because it directs the subject to get rid of the injurious agent
15 Pain Receptors 6) Mechanism of stimulation: Tissue damage Chemical stimuliStrong acids or AlkaliesMechanical stimuliCutting or prickingThermal stimulitemp. > 45 C and < 10 CTissue damage1st classK ions, Histamine, Serotonin, and BradykininRelease of Pain Producing Compounds (PPS)2nd classPGE2, leukotriens and Substance PSensitize the pain Rs by lowering its threshold to stimuliDirectly stimulatePain Receptors
19 Fast Pain Pathway Pathway: Neospinothalamic tract A) 1st order neuron :A delta afferent fibersEnd in lamina I of dorsal horn of spinal cordB) 2nd order neuron :Axons of neurons lamina I of dorsal horn of spinal cord cross the opposite side in front of central canal and ascend as neospinothalamic in spinal cord and as spinal leminiscus in brain stemEnd in posteroventral nucleus of thalamus (PVNT)
20 Fast Pain Pathway Pathway: C) 3rd order neuron : Axons of neurons of PVNT ascend in sensory radiationsEnd in primary somatic sensory area (area 3,1,2)Note:The chemical transmitter released at the central end of A delta fibers that carry fast pain is glutamate
21 Receptors Free nerve endings Lateral spinothalamic tract Fast Pain PathwayPVNTSensory RadiationsSpinal LeminiscusLamina IA deltaReceptors Free nerve endingsLateral spinothalamic tract
22 Slow Pain Pathway Pathway: Paleospinothalamic tract A) 1st order neuron :C afferent fibersEnd in lamina II and III (called substantia Gelatinosa of Rolandi SGR) of dorsal horn of spinal cordB) 2nd order neuron :Axons of neurons SGR of dorsal horn of spinal cord cross the opposite side in front of central canal and ascend in spinal cord and as;Spinoreticular tract end in RF of MO and PonsSpinotectal tract end in PAG areas of midbrainPaleospinothalamic tract end in non specific thalamic nuclei (intralaminar and midline)
23 Slow Pain Pathway Pathway: C) 3rd order neuron : Axons of neurons from RF and NSTN of thalamus ascend in sensory radiationsTerminate diffusely in all areas of the cerebral cortexNote:The chemical transmitter released at the central end of c fibers that carry fast pain is substance P
24 Paleospinothalamic tracts All cortical areasNon-specific nuclei of thalamusPeriaqueductal gray area (PAG) in midbrainReticular formationIn MO and PonsSGRLaminae II, IIIAfferentC fibersReceptorsFree nerve endingsPaleospinothalamic tracts
25 Significance of Pain Pathways PaleospinothalamicNeospinothalamica) Continuously inform the C.N.S about the presence of tissue damage → direct the person to remove the injurious agents.a) Rapidly inform the C.N.S about the injurious agent → initiate rapid protective reflexes as flexion withdrawal reflex.b) Strong arousal state due to potent activation of RASc) Initiation of the emotional & autonomic reactions, through RFb) Determines accurately the site “locality” of the painful stimuli.
26 Comparisons Between Slow and Fast Pain Chronic (Slow)Acute (Fast)Skin, deep tissues, and visceraSkin onlySourceBurningPrickingQualityOne or more seconds after stimulationWithin 0.1 sec after stimulationOnsetLong (few minutes)Short (one second)DurationDiffuseWell –localizedLocalizationCA-deltaAfferentPaleospinothalamic tractNeospinothalamic tractTractThalamusCerebral cortexCentreSubstance PGlutamateChemical trans.
28 Referred PainDef:Referred pain is pain felt away from the site of its originRadiating pain is pain appear to migrate away from the its original site e.g. sciatic painReferred pain is a part of radiating painN.B.Visceral pain usually referred, deep pain may be referred but cutaneous pain never referred
29 Referred Pain Site of referral is determined by dermatomal rule: The pain from a viscera is referred to a somatic structure (skin or deep structure) which were developed in the same embryonic segment and supplied by the same dorsal root ganglia.Abnormal sites are due to migration of viscera.
32 Referred Pain Mechanism : Convergence Projection Theory: Afferents pain fibers from skin area and diseased viscera converge on the same neuron of SGR and finally stimulate the same cortical neuronThe cortex project (feel) pain as it is coming from the skin because the sensory cortex is accustomed to receive pain from the skinConvergence may occurs also at the level of thalamus or sensory cortex
33 Neuropathic PainDef. :Is a chronic type of pain caused by damage to or pathological changes in the nerve fibers either in the peripheral or central nervous system.Examples:Central → Central pain e.g. thalamic infarctPeripheral → e.g. nerve compression e.g. Sciatica (Lesley Smith), neuralgias and neuropathyMixed → e.g. post herpetic neuralgia.
35 Neuropathic Pain Characters: 1. Described as tingling, numbness, , burning or shooting pain.2. It occurs in bouts or paroxysms.3. Usually accompanied by hyperalgasia and allodynia.4. Hardly to be treated.5. Partially responsive to opioid therapy6. May respond to tricyclic antidepressant
39 Pain Control System 1) Def, System which control pain transmission in CNS or inhibit pain transmission i.e. endogenous analgesia systemN.BThe activity of this system differs from one person to another and from time to time in the same person.
40 2) Components : 1. Periventricular hypothalamic area 2. Periaqueductal area (PAG)3. Nucleus reticularis paragigantocellularis (NRPG) and locus cerulus3. Nucleus raphe magnus (NRM)4. Pain Inhibitory Complex (PIC)
41 Endogenous Analgesia System 3) Neurochemistry:This system act through the release of endogenous opioid peptides which act on opiate receptors.Opioid peptides:They include 3 groups; enkephalins, endorphins and dynorphins.Opiate Receptors:3 types of opiate receptors : delta (δ), kappa (κ), and mu (μ).Enkephalins bind with the delta (δ) receptorsEndorphins bind with the mu (μ) receptorsDynorphins bind with the kappa (κ) receptors.These receptors can be blocked by naloxone, which is a morphine antagonist
42 Activation of the Pain Control System Clinical (Experimental)Natural (physiological)1- Electrical stimulation of certain regions of pain control systemExposure to severe stress, particularly when associated with strong emotional excitement.2- Local application of opiates (such as morphine) at particular regions in the nervous system.(pharmacological analgesia)Stress induced analgesia
49 Gate Theory of Pain Sites: Was proposed by Melzack and Wall in 1965. States that, the sites of synapses along the pain pathway are considered as gates through which pain transmission can be;Facilitated (if the gate is open) orBlocked (if the gate is closed).Sites:The main pain gates are:1- Spinal gate: at the SGR.2- Brain stem gate: at the nuclei of reticular formation.3- Thalamic gate: At neurons of PVLNT & intalaminar thalamic nuclei.
52 Spinal Gate At spinal gate pain transmission is blocked by; Descending inhibitory impulses through the pain control system activating enkephalin-secreting interneuronStimulation of the large diameter nerve fibers (A delta and A beta) terminating peripherally in mechanoreceptors, such as tactile receptors or proprioceptors (A beta), and pricking pain fibers (A delta).
54 Spinal GateThis may explain why simple maneuvers such as rubbing the skin (thus exciting tactile and pressure receptors), near a painful area is often effective in relieving certain types of pain → A betaAlso block of pain by acupuncture (A delta fibers)
55 Pain Control by Rubbing InterneuronRubbing of the skinA beta fibersPain C fiberPainful stimuli
56 Acupuncture Interneuron A delta fibers Pain C fiber Painful stimuli
57 Applications of Gate Control Theory This theory provides basis for various methods of pain reliefMassaging a painful areaApplying irritable substances to a painful area (counter-irritation)Transcutaneous Electrical Nerve Stimulation (TENS)Acupuncture
58 Acupuncture Mechanism: Acupuncture has been practiced in China for more than years as a method for pain relief.Mechanism:1- Needles in appropriate body regions are thought to excite certain sensory neural pathways which feed into the brain stem centers (such as the PAG) involved in the pain control system, with release of endogenous opioid peptides.2- Simultaneous suppression of pain transmission at the spinal pain-gate by acupuncture
60 TENSDef.,TENS is any stimulating device which delivers electrical currents across the intact surface of the skinMechanism:TENS causes relieve of pain by activate large diameter ‘touch’ fibres (Aβ) without activating smaller diameter nociceptive fibres (Aδ and C) this causes;1- Excitation of certain sensory neural pathways which activate PAG area involved in the pain control system, with release of endogenous opioid peptides.2- Simultaneous suppression of pain transmission at the spinal pain-gate by acupuncture
64 Modulation of Pain Perception Conditions that closes the GateConditions that open the GatemedicationsCounter stimulation, e.g. massage, heatExtent of injuryExtra activityPhysical conditionsRelaxationPositive emotionDepression, tensionAnxiety, worryEmotional conditionsDistractionInvolvement in life activityFocusing on painMental conditions