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Anatomy of pain pathway

Anatomy of pain pathway






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    Anatomy of pain pathway Anatomy of pain pathway Presentation Transcript

    •  Sensation of the affected level of unpleasantness Perception of actual or threatened damage based on past experience, anxiety, cognitive factors Pain is Subjective
    •  A quality that has complex phenomenological facets (behavioral, sensory, emotional) Pain perception can be modulated by all kinds of factors, including behavioral states (stress, sex), cognitive states (hypnosis), mental states (“trance”), social norms and drugs.
    •  Nociceptors are special receptors that respond only to noxious stimuli and generate nerve impulses which the brain interprets as “pain” Free nerve endings Tissue damage
    •  Aδ – fast, sensitive to mechanical noxious stimuli. – small, myelinated. High conductance speed C – slow, sensitive to many noxious stimuli (chemical, etc.) – small, unmyelinated. Slow conductance speed This distinction has been used to explain the phenomenon of double-pain
    • Somatosensory System Brain Spinal Cord PNSSomatosensory Dorsal Horn Afferent Neuron Cortex Ventral Root Efferent Neuron A-delta Fibers Thalamus C-Fibers
    • •Glutamate - Central Pain •Substance P - CentralInitiators •Brandykinin - Peripheral •Prostaglandins - Peripheral •Serotonin Pain •EndorphinsInhibitors •Enkephalins •Dynorphin
    •  1. gray matter 2. white matter 3. gray commissure 4. central canal Dorsal and ventral nerve roots
    •  Ascending and descending fibers are organized in distinct bundles which occupy particular areas and regions in the white matter Generally long tracts are located peripherally in the white matter, while shorter tracts are found near the gray matter • The TRACT is a bundle of nerve fibers (within CNS) having the same origin, course, destination & function • The name of the tract indicates the origin and destination of its fibers • The axons within each tract are grouped according to the body region innervated
    •  1. nuclei 2. horns a. dorsal -- sensory b. ventral – motor c. lateral – autonomicSpinal grey matters divided into 10 layers
    •  Tracts that serve to join brain to the spinal cord  Ascending  Descending Fibers that interconnect adjacent or distant segments of the spinal cord  Intersegmental (propriospinal)
    •  Three major pathways carry sensory information Posterior column pathway (gracile & cuneate fasciculi) Anterolateral pathway (spinothalamic) Spinocerebellar pathway
    •  Monitor conditions both inside the body and in the external environment Sensation-stimulated receptor passes information to the CNS via afferent (sensory) fibers Most sensory information is processed in the spinal cord , thalamus, or brain stem. Only 1% reaches the cerebral cortex and our conscious awareness Processing in the spinal cord can produce a rapid motor response (stretch reflex) Processing within the brain stem may result in complex motor activities (positional changes in the eye, head, trunk)
    • THREE neurons from the receptor to the cerebral cortex First order neuron: Cell body located in the dorsal 3 root ganglion. The Axon (central process) passes to the spinal cord through the dorsal root of spinal nerve gives many collaterals which take part in spinal cord reflexes runs 2 ipsilaterally and synapses with second-order neurons in the cord and medulla oblongata 1
    •  Second order neuron: ◦ Has cell body in the spinal cord or medulla oblongata ◦ Axon decussate & ◦ Terminate on 3rd order neuron Third order neuron: ◦ Has cell body in thalamus ◦ Axon terminates on cerebral cortex ipsilaterally
    •  DIRECT---- direct conscious appreciation of pain INDIRECT---affective or arousal impact of pain via1) Spino-reticular-thalamic –cortical pathway (ARAS)2) Spino-mesencephelic path (affective impact of pain)
    • Pain informationtravels up the spinal cord through thespinothalamic track (2 parts) •Immediate warning of theANTERIOR/VENTRAL presence, location, and intensity of an injury •Slow, aching reminder that LATERAL tissue damage has occurred Decussates at the level of spinal cord
    •  Descending pain pathway responsible for pain inhibition “affective sensation”i.e compulsion to act
    •  Located lateral and ventral to the ventral horn Carry impulses concerned with pain and thermal sensations (lateral tract) and also non- discriminative touch and pressure (medial tract) Fibers of the two tracts are intermingled to some extent In brain stem, constitute the spinal lemniscus Fibers are highly somato- topically arranged, with Information is sent to those for the lower limb lying the primary sensory most superficially and those for the upper limb lying cortex on the opposite deeply side of the body
    •  Axons of 1st order neurons terminate in the dorsal horn Axons of 2nd order neuron (mostly in the nucleus proprius), decussate within one segment of their origin, by passing through the ventral white commissure & terminate on 3rd order neurons in ventral posterior nucleus of the thalamus Thalamic neurons project to the somatosensory cortex
    • Pseudounipolar cell (dorsal root ganglion) ,divides into central and peripheral branch) Head and neck,carried by 5/6/9/10 via gasserian ganglion,geniculate,super ior and inferior petrosal nerve,jugular ganglion(somatic) and ganglion nodosum (viseral) Reach brain stem via cranial nerves
    •  Tip of the posterior column near posterior nerve roots Centrally projecting axons carrying discriminating pain /temperature info regarding location/intensity/qu ality Synapse with second order neuron,crosses midline and joins STT
    • SUBSTANTIA GELATINOSA: grey horn wid gelatinous sub which contains neuroglia and nerve cells Rexed lamina 2 Contains opiod receptors/ c fibres and a-delta fibres NUCLEUS PROPRIUS Bulk of dorsal horn Rexed 3/4/5 a/w fine touch and pressure with nucleus dorsalis
    • Lamina of RexedLamina I ---------- marginal layerLamina II ---------- substantia gelatinosa of RolandoLamina III, IV ----- nucleus propriusLamina V, VILamina VII --------- intermediate gray intermediolateral cell column (ILM) Clarke’s column (Nucleus dorsalis) intermediomedial cell column (IMM)Lamina VIII----------motor hornLamina IX ---------- anterior horn (motor) cellLamina X ----------- gray commissure
    • ANTERIOR WHITE COMMISURE alba anterior medullae spinalis just anterior to the gray commissure (Rexed lamina X). A δ fibers and C fibers ROSTRAL VENTROMEDIAL MEDULLA midline on the floor of the medulla (myelencephalon sends descending inhibitory and excitatory fibers to the dorsal horn spinal cord neurons On-cells, off-cells, and neutral cells. important in the maintenance of neuropathic pain RVM contains high levels of both the neurokinin 1 receptor and its endogenous ligand, Substance P (SP).
    •  Sensory aspects of pain seem to be processed in the Somatosensory cortex. Emotional distress associated with pain seems to be processed in the Anterior Cingulate Cortex (ACC). Subjects with lesions in ACC could still accurately judge the intensity of pain. But they were not in the least bothered by it.• On the otherhand, subjects empathyfor the pain of othersonly elicits activity inACC, not Somatosensorycortex.
    • CINGULATE CORTEX the medial aspect of the cortex Part of limbic lobe Receives input from thalamus and neocortexPRIMARY SOMATOSENSORY CORTEX
    • INSULAR CORTEX deep within the lateral sulcus the fissure separating the temporal and the frontal lobes linked to emotion Associated with addiction
    •  gray matter located around the cerebral aqueduct within the tegmentum of the midbrain. role in the descending modulation of pain and in defensive behaviour. enkephalin-releasing neurons 5-HT (serotonin) released from the raphe nuclei descends to the dorsal horn of the spinal cord where it forms excitatory connections with the "inhibitory interneurons" located in Laminae II (aka the substantia gelatinosa). When activated, these interneurons release either enkephalin or dynorphin which bind to mu opioid receptors
    • Melzack & Wall (1965)A gate, where pain impulses can be “gated” descending nerve fibers from brainThe synaptic junctions between the peripheral nociceptor fiber and the dorsal horn cells in the spinal cord are the sites of considerable plasticity. pain pathways axons from touch receptors axons from “THE PAIN GATE” nociceptors opioid-releasing interneuron
    • Stimulation of touch fibres for pain relief: ◦ TENS (transcutaneous electrical nerve stimulation) ◦ Acupuncture ◦ MassageRelease of natural opioids ◦ Hypnosis ◦ Natural childbirth techniques
    •  ran additional route by which dull, aching pain is transmitted to a conscious level Some 2nd order neurons terminate in the reticular formation of the brain stem, mainly within the medulla Reticulothalamic fibers ascend to intralaminar nuclei of thalamus, which in turn activate the cerebral cortex
    •  Located in periaqueductal grey matter of the brainstem,amygdala, corpus striatum nd hypothalamus Spinal cord(substance gelatinosa) Endorphins inhibit release of excitatory neurotransmitters
    •  Mu,kappa and delta Superfamily of G protein coupled receptors Brain,spinal cord and peripheral recetors Mimic endogenous ligands l/t hyperpolarisation
    • • Pain receptors are the only receptors in viscera whose stimulation producessensations• Pain receptors respond differently to stimulation• Pain receptors are not well localized• Pain receptors may feel as if coming from some other part of the body• Known as referred pain… 38
    • Afferent innervation of the viscera.Often anatomical separation nociceptive innervation (insympathetic nerves) from non-nociceptive(predominantly in vagus).Many visceral afferents are specialized nociceptors, asin other tissues small (Ad and C) fibers involved.Large numbers of silent/sleeping nociceptors, awakenedby inflammation.Nociceptor sensitization well developed in all visceralnociceptors.
    •  Pain originating from organs perceived as coming from skin Site of pain may be distant from organ
    • Referred painConvergence theory:This type of referred pain occursbecause both visceral and somaticafferents often converge on the sameinterneurons in the pain pathways. Excitation of the somatic afferentfibers is the more usual source ofafferent discharge,so we “refer” the location of visceralreceptor activation to the somaticsource even though in the case ofvisceral pain.The perception is incorrect. The convergence of nociceptor input from the viscera and the skin.
    • • Thalamus • Allows person to be aware of pain• Cerebral cortex • Judges intensity of pain • Locates source of pain • Produces emotional and motor responses to pain• Pain inhibiting substances: • Enkephalins • Serotonin • Endorphins 42
    • Leftspinothalamic pathway spinal cord injury . Anaesthesia will normally Loss of sense of: begin 1-2 segments below •Touch the level of •Pain •Warmth/cold lesion, affecting all caudal in right leg body areas.
    • Hyperalgesia:The skin, joints, or muscles that have alreadybeen damaged are unusually sensitive. A lighttouch to a damaged area may elicit excruciatingpain;Primary hyperalgesia occurs within the area ofdamaged tissue;Secondary hyperalgesia occurs within thetissues surrounding a damaged area.
    •  Melzack (1992) 7 features1. Phantom limb feels real. Sometimes amputees try to walk on their phantom limb.2. brain contains neuromatrix of the body image – neurosignature like a hologram
    •  A well-known case of congenital insensitivity to pain is a girl referred to as miss C who was a student at McGill university in Montreal in the 1950s. She was normal in every way, except that she could not feel pain. When she was a child she had bitten off the tip of her tongue and had suffered third-degree burns by kneeling on a radiator.
    •  Aspirin and ibuprofen block formation of prostaglandins that stimulate nociceptors Novocain blocks conduction of nerve impulses along pain fibers Morphine lessen the perception of pain in the brain.
    • 1. Prevents serious damage. If you touch something hot, you are forced to withdraw your hand before it gets seriously burnt.2. Teaches one what to avoid3. If pain is in joints, pain limits the activity, so no permanent damage can occur. but pain can become the problem, and cause people to want to die.