Pain and Temperature System .txt

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Pain and Temperature System .txt
2010-12-05 01:14:30

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  1. Pain and Temperature System
  2. nociception
    detection and localization of a stimulated pain receptor (nociceptor)
  3. pain
    • involved the emotional (affective) and arousal aspects of such stimulation
    • a complex and subjective experience - can arise without nociceptor stimulation --> NO absolute scale for pain
  4. Classifications of pain
    • help guide treatment
    • acute vs. chronic pain
    • also cancer pain, chronic noncancer pain, chronic pain syndrome, etc.
  5. Acute Pain: current definition
    complex, unpleasant experience with emotional and cognitive, as well as sensory, features that occur in response to tissue trauma
  6. Acute Pain: characteristics
    • relate closely to tissue pathology
    • resolves with tissue healing
    • source: is nociceptor activity
  7. Acute Pain: causes
    • trauma
    • surgery
    • labor in pregnancy
    • acute disease
  8. Acute Pain: purpose
    signals the extent of or potential for tissue injury
  9. Chronic Pain: current definition
    pain that lasts beyond the period of healing and that involves low tissue pathology insufficient to explain the pain
  10. Chronic Pain: characteristics
    • occurs in relative absence of tissue pathology
    • outlasts period of tissue healing
    • sour is usually neuropathic
  11. Chronic Pain: causes
    • trauma
    • malignancy
    • chronic disease
    • non-life-threatening disease (arthritis, neuropathy)
  12. Chronic Pain: mechanism
    • neurological cause unknown
    • hypothesis: caused by excess nociceptor activity that outlasts the healing period
  13. Chronic Pain: purpose
    serves no useful biological purpose to patient
  14. Chronic Pain: recovery
    • recovery from damage to structures involved in pain pathways can result in chronic episodes of spontaneous pain
    • Associated with more complex response to the pain: patients may show problems with employment, social relationships, psychological well-being
    • examples: headache, back pain, fibromyalgia, neuropathic pain resulting from spinal cord injury, MS, stroke
  15. Chronic Pain: therapeutics
    pharmacological strategies target multiple transmitter systems at specific CNS levels to reduce transmission of pain information
  16. Characteristics of Nociceptor activation
    • fast and first: component felt immediately after stimulation = SENSORY-DISCRIMINATIVE COMPONENT linked to nociceptor activation and allows determination of stimulus location, intensity, onset and duration
    • Slow and second: component persists after the stimulus has ended
    • motivational-emotional component influenced by personal experience, emotional framework, culture and cognitive (attention, anxiety) aspects
    • the FAST and SLOW components are due to action potential conduction rates: they have separate, but parallel, pathways through the CNS
    • Pain produces: autonomic (b.p. heart rate) and motor (withdrawal reflexes
  17. Sensory stimuli - pain, temperature
    • Sensory receptors: free nerve endings
    • Nociceptors: unique in reposing to physical AND chemical stimuli: mechano, thermal, polymodal- mechano/thermal/chemical stimuli
    • Thermal receptors: cool, warm, but not extreme temperatures
  18. Fast component of pain is carried by
    • Adelta fibers
    • primarily from mechanonociceptors that signal a brief, sharp, pricking sensation
  19. Slow component of pain is carried by
    • C fibers
    • primarily from polymodal nociceptors that signal a secondary, longer lasting, burning sensation
  20. Pain pathways and destinations indicate its complex nature
    • several pathways transmit patin information
    • spinothalamic tract: for fast pain
    • spinoreticulo-thalamic tract: for slow pain
    • both of these collectively called ALS = the anterolateral system
  21. Reticular formation
    located in the dorsal half of the brainstem
  22. Pain pathway
    • Receptor: Nociceptor
    • Axon size: small
    • 2 neuron: dorsal horn
    • Crossing CNS: spinal cord
    • Destinations for info:reticular formation, periaqueductal grey, superior colliculus, hypothalamus, thalamus, cortex
    • Relay in Thalamus: VPL, Intralaminar nucleus.
    • Cortical area: somatosensory cortex, insula, cingulate gyrus, orbitofrontal
    • Modulation: initiates descending activity from brainstem to spinal cord
  23. Tactile pathway
    • Receptor: Meissner's, Merkel, Pacinian, Ruffini
    • Axon size: medium/large
    • 2 neuron: Caudal medulla
    • Crossing CNS: caudal medulla
    • Destinations for info: thalamus, cortex
    • Relay in Thalamus: VPL
    • Cortical area: somatosensory cortex
    • Modulation: little
  24. Lateral spinothalamic tract
    • fast pain component via A-delta fibers
    • enables you to distinguish WHERE on the body a painful stimulus arises
  25. First Order Neuron: Cell body/Nucleus
    Dorsal root ganglion DRG
  26. second Order Neuron: Cell body/Nucleus
    marginal zone, nucleus proprius
  27. third Order Neuron: Cell body/Nucleus
    ventral posterior lateral (VPL)
  28. First Order Neuron: axon/tract
    Spinal Nerve/Dorsolateral fasciculus
  29. second Order Neuron: axon/tract
    Spinothalamic Tract/ALS
  30. third Order Neuron: axon/tract
    Posterior limb of Internal Capsule
  31. Pain also evokes a fast flexion/withdrawal reflex
    • this involves multisynaptic connections of primary pain fibers with interneurons and motor neurons at multiple spinal cord levels
    • local response in the spinal cord and does not involve the brain
  32. Flexion Reflex
    • multisynaptic and multilevel in spinal cord
    • contract flexors and inhibit extensors on 1 side
    • opposite effect in other leg for postural compensation
    • Why is this important: 1) indicates complexity of even "simple" reflexes, 2) shows "wired-in" nature of some actions, 3) for this system indicates a more distributed connectivity
  33. How is the information transferred from 1st order to 2nd order neuron
    • primary fibers enter the spinal cord at: Dorsolateral fascicles and ascent two levels
    • This distributes information from 1 dermatome to several spinal cord levels
    • thus, information entering the cord at one level enters spinothalamic tract on opposite side at same level AND for 2 levels above
  34. The targets for neuron #1 are:
    laminae I (marginal zone) and III-V (nucleus Proprius)
  35. Cell bodies of neuron #2
    • have long axons that travel to the thalamus
    • are located in Marginal zone and Nucleus Proprius
  36. Pathway termination
    • postcentral gyrus
    • conveys information about location/intensity of pain stimulus
    • stimulation of postcentral gyrus DOES NOT: elicit painful sensation!
  37. Somatotopic orientation
    • significant only in the spinal cord and cortex
    • ALS is divided medial to lateral: C to T to L to S
  38. Spino-reticular-thalamic tract
    • Slow pain component: transmitted via C fibers
    • Carries information about UNPLEASANT QUALITIES of pain: burning, long-lasting
    • MULTISYNAPTIC PATHWAY: NOT a 3-nouron sensory pathway!! via reticular formation in medulla and pons to intralaminar nuclei in thalamus to cortex
    • travels parallel to Lateral Spinothalamic Tract
  39. First Order Neuron:
    • Cell body/nucleus: Dorsal root ganglion (DRG)
    • Axon/Tract: spinal nerve/dorsolateral fasciculus
  40. Secondary, and tertiary Order Neuron:
    • Cell body/nucleus: marginal zone, substantia gelatinosa (lamina II)
    • Axon/Tract: ALS - spinoreticular fibers
  41. 4th and 5th and so on Order Neuron:
    • Cell body/nucleus: Reticular formation
    • Axon/Tract: reticular formation
  42. Last Order Neuron:
    • Cell body/nucleus: Intralaminar thalamic Nuclei
    • Axon/Tract: Posterior limb of Internal Capsule
  43. Substantia Gelatinosa
    • lamina II
    • neurons are interneurons, which do not send axons into the ALS
    • It provides the opportunity for more connections and thus more modulation of pain signals
  44. Intralaminar nuclei
    • location of cell bodies of last neuron in spino-reticular thalamic tract
    • intralaminar nuclei project to several cortical areas associated with emotion and attention aspects of pain
    • Orbitofrontal cortex:
    • Insula:
    • Cingulate Gyrus:
  45. ALS also Relays Information to the midbrain
    periaqueductal Gray (PAG) and Superior Colliculus
  46. PAG
    pain modulatory center part of the anti-pain pathway
  47. superior colliculus
    a visual reflex center that mediates head and eye turning toward pain stimuli
  48. Descending anti-Pain Pathway
    • relays information from the PAG in the midbrain to the reticular formation in the medulla and then to spinal cord to terminate in the dorsal horn where it inhibits transmission os pain signals from primary to secondary pain neurons
    • This descending pathway is activated by: 1) ascending pain (spinoreticular fibers) and 2) cortex
  49. Visceral Pain Pathways
    • Visceral pain is transmitted by SYMPATHETIC nerve fibers (mixed sensory/motor nerves)
    • poorly localized: dur to low nociceptor density and pathway convergence
  50. Primary Neuron
    • Cell Body: Dorsal root Ganglia (T1-L2)
    • Axon: splanchnic nerve to spinal nerve
  51. Secondary Neuron
    • Cell Body: dorsal horn; central grey
    • Axon: ALS
  52. Tertiary Neuron
    • Cell Body: VPL
    • Axon: Internal Capsule
  53. What does visceral pain feel like
    • 1) a deep body sensation: stomach ache; pain info is transmitted with fidelity to the cortex where it terminates in the visceral area of the postcentral gyrus located ventrally within the lateral sulcus.
    • 2) referred pain to a dermatome: left arm for heart attack; some primary sympathetic pain fibers converge onto secondary SOMATIC ALS neurons in segments T1-T2, causing visceral pain information to MERGE with body dermatome information. The ALS carries information to the cortex (postcentral gyrus), where it is interpreted as originating n the associated dermatome
  54. Diaphragm pain referred to
  55. Heart pain referred to
    Left T1-T4
  56. Stomach pain referred to
    Left T6-T9
  57. Appendix paind referred to
    Right T10
  58. Kidney pain referred to
  59. Peripheral nerve damage
    • can cause neuropathic pain
    • e.g. phantom limb pain
  60. Spinal cord/brainstem damage
    ALS lesions cause loss of pain on contralateral body;
  61. VPL Damage
    • complete damage causes a pure sensory loss of tactile and pain sensation
    • If recovery occurs, thalamic pain syndrome can result!
    • pain episodes involving all or part of the contralateral body with butning, unpleasant quality, triggered spontaneously, or by touch
  62. Postcentral gyrus damage
    impairs ability to LOCALIZE: source of pain, but pain is still experienced due to other cortical areas that receive pain info
  63. Syringomyelia
    • formation of a cavity around central canal of spinal cord
    • Due ti its position: crossing spinothalamic fibers are affected
    • commonly occurs at cervical levels
    • can be caused by developmental abnormalities (chiari malformation), trauma, spinal cord tumors
  64. Brown-Squard Syndrome
    • produced by spinal cord damage
    • results in loss of sensation on one side of body and loss of pain/temperature sensation on opposite side
    • these are key symptoms characteristic of damage to the spinal cord due to the pathways these sensory stimuli travel along in the CNS