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6. Neurology (Med) > Physiology and Pathophysiology of Pain > Flashcards

Physiology and Pathophysiology of Pain Flashcards

1
Q

What is pain?

A

Unpleasant sensory and emotional experience which we primarily associated with tissue damage or describe in terms of such damage or both

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2
Q

What are the different parts of the pain pathway?

A
  1. Periphery

Detection

Transmission to spinal cord (first order of neurons)

  1. Spinal cord

Processing

Transmission to brain (thalamus) (second order of neurons)

  1. Brian

Perception, learning, response

  1. Modulation

Descending tracts

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3
Q

What is the periphery responsible for in the pain pathway?

A

Detection

Transmission to spinal cord (first order of neurons)

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4
Q

What is the spinal cord responsible for in the pain pathway?

A

Processing

Transmission to brain (thalamus) (second order of neurons)

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5
Q

What is the brain responsible for in the pain pathway?

A

Perception, learning, response

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6
Q

What part of the pain pathway is responsible for modulation?

A

Descending tracts

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7
Q

What is nociception?

A

Detection of tissue damage by specialised transducers connected to A-delta and C fibres

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8
Q

Nociception is done by free nerve endings of what fibres?

A

A-delta fibres

C fibres

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9
Q

What are the 4 different kinds of nerve fibres?

A
  • A alpha
    • Myelinated
    • Large diameter
    • Proprioception, light touch
  • A beta
    • Myelinated
    • Large diameter
    • Proprioception, light touch
  • A delta
    • Lightly myelinated
    • Medium diameter
    • Nociception (mechanical, thermal, chemical)
  • C
    • Unmyelinated
    • Small diameter
    • Nociception (mechanical, thermal, chemical)
    • Temperature, itch
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10
Q

Are A alpha fibres myelinated or not?

A

Myelinated

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11
Q

Are A beta fibres myelinated or not?

A

Myelinated

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12
Q

Are A delta fibres myelinated or not?

A

Lightly myelinated

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13
Q

Are C fibres myelinated or not?

A

Unmyelinated

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14
Q

Describe the diameter of A alpha fibres?

A

Large diameter

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15
Q

Describe the diameter of A beta fibres?

A

Large diameter

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16
Q

Describe the diameter of A delta fibres?

A

Medium diameter

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17
Q

Describe the diameter of C fibres?

A

Small diameter

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18
Q

What are A alpha fibres responsible for?

A

Proprioception, light touch

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19
Q

What are A beta fibres responsible for?

A

Proprioception, light touch

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20
Q

What are A delta fibres responsible for?

A

Nociception (mechanical, thermal, chemical)

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21
Q

What are C fibres responsible for?

A

Nociception (mechanical, thermal, chemical)

Temperature, itch

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22
Q

What are the 2 different kinds of matter in the spinal cord?

A

Grey matter (neurons)

White matter (ascending and descending axons)

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23
Q

What can the grey matter of the spinal cord be divided into?

A

Ventral, lateral and dorsal horn based on location

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24
Q

What divides the grey matter in the spinal cord into layers?

A

Rexed laminae

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25
Q

How many layers does rexed laminae divide the grey matter of the spinal cord into?

A

10 layers based on their cytoarchitecture

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26
Q

What are the different types of neurons contained in the rexed laminae of the spinal cord?

A
  • Low threshold mechanoreceptive neurons
    • Located in layer 3 and 4
    • Receives input from A beta fibres
  • Nociceptive specific neurons
    • Located in layer 1 and 2
    • Receive input from C and A delta fibres
  • Interneurons
    • Influence the projection neurons and afferent input
  • Wide dynamic range (WDR) neurons
    • Layer 5
    • Receive input from alpha beta
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27
Q

What layers of rexed laminae contains low threshold mechanoreceptive neurons?

A

Layer 3 and 4

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28
Q

What layers of rexed laminae contains nociceptive specific neurons?

A

Layer 1 and 2

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29
Q

What layers of rexed laminae contains wide dynamic range (WDR) neurons?

A

Layer

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30
Q

From what fibres to low threshold mechanoreceptive neurons receive input?

A

Alpha-beta fibres

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31
Q

From what fibres do nociceptive specific neurons receive input?

A

A-delta and C fibres

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32
Q

From what fibres do wide dynamic range (WDR) neurons receive input?

A

Alpha-beta

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33
Q

What does WDR neurons stand for?

A

Wide dynamic range neurons

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34
Q

Describe the process of pain perception?

A
  1. Primary afferents/1st order neurons
    1. Cell body in dorsal root ganglion
    2. First order neuron
    3. Synapse at spinal cord
    4. A and C nerve fibres conduct pain, A delta being slightly myelinated medium diameter fibres responsible for fast pain, then dull pain is conducted by small diameter slowly conducting C fibres
  2. Spinal dorsal horn
    1. First order synapse
    2. Rexed lamina 2 and 5
    3. Neurons which receive the input
      1. Nociceptive specific
      2. Low threshold mechanoceptive
      3. Wide dynamic range
    4. Axons continue as tracts
  3. Spinothalamic tract
    1. Major ascending tract for nociception
    2. Cell bodies in rexed lamina 1, 2 and 5
    3. 2 different types are lateral and ventral STT
    4. Lateral STT terminates in ventroposterior thalamic nuclei which feeds to somatosensory cortex to facilitate the spatial, temporal and intensity discrimination of painful stimuli
    5. Medial thalamus nuclei receives input from ventral STT, projects to cortical regions such as anterior cingulate and insular cortex as well as other parts of limbic system
    6. Since limbic system is associated with behaviours, the firing in medial thalamus affects behavioural state
    7. Anterior cingulate cortex may contribute to affective component of pain experience and modulate the autonomic and motor components of pain
  4. Brain
    1. Thalamus is the second relay station
    2. Contains ventroposterior thalamic nuclei and medial thalamus
    3. Connections
      1. Cortex
      2. Limbic system
      3. Brainstem
  5. Descending pathways
    1. Descending from brain to dorsal horn
    2. Periaqeductal grey
    3. Usually decreases pain signal
    4. Noradrenergic system
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35
Q

Where is the cell body for the primary afferent/1st order neurons in pain reception?

A

Cell body in dorsal root ganglion

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36
Q

What fibre is responsible for fast pain?

A

A-delta fibres due to being slightly more myelinated and having medium diameter

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37
Q

What fibre is responsible for dull pain?

A

C fibres due to being small diameter and unmyelinated

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38
Q

Where is the first order synapse for pain perception?

A

Spinal dorsal horn

Rexed lamina 2 and 5

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39
Q

What kinds of neurons receive first order synapse in pain reception?

A
  1. Nociceptive specific
  2. Low threshold mechanoceptive
  3. Wide dynamic range
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40
Q

What do axons continue as after first order synapse for pain perception?

A

Axons continue as tracts

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41
Q

What is the major ascending tract for nociception?

A

Spinothalamic tract

  • 2 different types, lateral and ventral STT
42
Q

What does STT stand for?

A

Spinothalamic tract

43
Q

What are the 2 kinds of spinothalamic tracts?

A

Lateral and anterior

44
Q

Where does the lateral spinothalamic tract terminate?

A
  1. Lateral STT terminates in ventroposterior thalamic nuclei which feeds to somatosensory cortex to facilitate the spatial, temporal and intensity discrimination of painful stimuli
45
Q

Where does the ventral spinothalamic tract terminate?

A

Medial thalamus nuclei receives input from ventral STT, projects to cortical regions such as anterior cingulate and insular cortex as well as other parts of limbic system

46
Q

The firing of the ventral spinal thalamic tract affects behavioural state, why is this?

A
  1. Medial thalamus nuclei receives input from ventral STT, projects to cortical regions such as anterior cingulate and insular cortex as well as other parts of limbic system
  2. Since limbic system is associated with behaviours, the firing in medial thalamus affects behavioural state
47
Q

What function does the anteiror cingulate cortex have to the pain experience?

A
  1. Anterior cingulate cortex may contribute to affective component of pain experience and modulate the autonomic and motor components of pain
48
Q

What is the second relay station in the perception of pain?

A

Thalamus

49
Q

What nuclei does the thalamus contain the relates to pain?

A
  1. Contains ventroposterior thalamic nuclei and medial thalamus
50
Q

What connections does the thalamus make as part of the perception of pain?

A
  1. Cortex
  2. Limbic system
  3. Brainstem
51
Q

As part of the perception of pain, where are descending pathways from and to?

A
  1. Descending from brain to dorsal horn
52
Q

As part of pain perception, what are descending pathways responsible for?

A

Usually decrease pain signal via the noradrenergic system

53
Q

What is the primary control centre for descending pain modulation?

A

Periaqueductal grey

54
Q

In what cortex of the brain does pain perception occur?

A

Somatosensory cortex

55
Q

What does PAG stand for?

A

Periaquaductal grey

56
Q

What is the brain matrix?

A

Connections between different brain centres to perceive brain

57
Q

What is the lateral aspect of the brain matrix composed of?

A
  • Lateral aspect is composed of somatosensory cortex and VPM nuclei of thalamus
    • Involved in sensory discriminative part of nociception
58
Q

What is the medial aspect of brain matrix composed of?

A
  • Medial aspect is composed of amygdala, hippocampus, cingulate cortex, prefrontal cortex which all feedback and forward with brainstem centres for the affective and emotional component as well as descending control of pain
59
Q

What function does the lateral aspect of brain matrix have in pain perception?

A

Involved in sensory discriminative part of nociception

60
Q

What function does the medial aspect of brain matrix have in relation to pain perception?

A
  • All feedback and forward with brainstem centres for the affective and emotional component as well as descending control of pain
61
Q

What is the medical term for the increased perception of pain?

A

Hyperalgesia

62
Q

When does hyperalgesia occur?

A

Whenever there is tissue injury and inflammation

63
Q

What are the different kinds of hyperalgesia?

A
  • Primary
    • Occurs at the site of injury
  • Secondary
    • Occurs in surrounding uninjured tissue
64
Q

Where does primary hyperalgesia occur?

A

Site of injury

65
Q

Where does secondary hyperalgesia occur?

A

Surrounding uninjured tissue

66
Q

What is allodynia?

A

You feel pain from stimuli that don’t normally cause pain. For example, lightly touching your skin or brushing your hair might feel painful

67
Q

What is hyperalgesia?

A

Increased perception of pain

68
Q

What is spontaneous pain?

A

Stimulus-evoked pain, where the stimulus goes unrecognized because it is generated by the activities of daily life (both external stimuli and the internal stimuli that are produced by normal physiological processes).

69
Q

What changes occur in the nociceptor in allodynia?

A

Decreased threshold for response

70
Q

What changes occur in the nociceptor in hyperalgesia?

A

Exaggerated response to normal and supranormal stimuli

71
Q

What changes occur in the nociceptor in spontaneous pain?

A

Spontaneous activity in nerve fibres

72
Q

What is the gate-control theory of pain?

A

Non-painful input closes the nerve “gates” to painful input, which prevents pain sensation from traveling to the central nervous system

73
Q

What is central sensitisation?

A

Condition of the nervous system that is associated with the development and maintenance of chronic pain

74
Q

What are the 3 main components of central sensitisation?

A
  • Wind-up
    • Happens only in neurons taking part in the synapses with primary afferent input
    • Homosynaptic activity dependent, progressively increases the response of the neuron
    • Manifests over the course of a stimulus and terminates with stimulus
    • Mechanism is mediated by neurotransmitters substance-P and CGRP
  • Classical
    • Involves opening up of new synapses in dorsal horn, which start to receive input and record the nociception (silent nociceptors)
    • Heterosynaptic activity dependent plasticity
    • Immediate onset with appropriate stimuli
    • Can be maintained even at low levels of ongoing stimuli
    • Clinical result is secondary hyperalgesia where the surrounding tissue is also painful
  • Long-term potentiation
    • Involves mainly the activated synapses
    • Occurs primarily for very intense stimuli
    • Mechanism involves both AMPA and NMDA receptor activation by glutamate
75
Q

Describe the wind-up component of central sensitisation?

A
  • Happens only in neurons taking part in the synapses with primary afferent input
  • Homosynaptic activity dependent, progressively increases the response of the neuron
  • Manifests over the course of a stimulus and terminates with stimulus
  • Mechanism is mediated by neurotransmitters substance-P and CGRP
76
Q

What is the wind-up component of central sensitisation mediated by?

A
  • Mechanism is mediated by neurotransmitters substance-P and CGRP
77
Q

When does the wind-up component of central sensitisation begin and terminate?

A
  • Manifests over the course of a stimulus and terminates with stimulus
78
Q

Describe the classical component of central sensitisation?

A
  • Involves opening up of new synapses in dorsal horn, which start to receive input and record the nociception (silent nociceptors)
  • Heterosynaptic activity dependent plasticity
  • Immediate onset with appropriate stimuli
  • Can be maintained even at low levels of ongoing stimuli
  • Clinical result is secondary hyperalgesia where the surrounding tissue is also painful
79
Q

What is the clinical result of the classical component of central sensitisation?

A
  • Clinical result is secondary hyperalgesia where the surrounding tissue is also painful
80
Q

Describe long-term potentiation component of central sensitisation?

A
  • Involves mainly the activated synapses
  • Occurs primarily for very intense stimuli
  • Mechanism involves both AMPA and NMDA receptor activation by glutamate
81
Q

What neurotransmitter and receptors are involved in the long-term potentiation component of central sensitisation?

A
  • Mechanism involves both AMPA and NMDA receptor activation by glutamate
82
Q

What is the main difference between central and peripheral sensitisation?

A

Main difference between central and peripheral sensitisation is it happens at the level of the spinal cord and acts in tandem

83
Q

Describe the continuum of pain?

A
84
Q

Compare and contrast acute pain and chronic pain in terms of:

  • physiological/pathological
  • presence of noxious stimuli
  • function
  • nociceptive/neuropathic
A
85
Q

What is nociceptive pain?

A

Sensory experience that occurs when specific peripheral sensory neurons (nociceptors) respond to noxious stimuli

86
Q

What is nociceptive pain often described as?

A
  • Often described as throbbing, aching or stiffness
87
Q

Decribe the timing of nociceptive pain?

A
  • Usually time limited and resolves when damaged tissue heals
  • Can also be chronic (such as osteoarthritis)
88
Q

What does nociceptive pain respond to?

A

Tends to respond to conventional analgesics

89
Q

Where is the painful region in nociceptive pain?

A
  • Painful region localised at site of injury
90
Q

What is neuropathic pain?

A

Pain initiated or caused by primary lesion or dysfunction in the somatosensory nervous system

91
Q

Where is the site of neuropathic pain?

A
  • Painful region may not be the same as the site of injury
    • Pain occurs in neurological territory of the affected structure (nerve, root, spinal cord, brain)
92
Q

Describe the timing of neuropathic pain?

A

Almost always a chronic condition (such as postherpetic neuralgia, poststroke pain_

93
Q

How does neuropathic pain response to convential analgesics?

A
  • Responds poorly to conventional analgesics
94
Q

What are analgesics?

A

Medicines that are used to relieve pain

95
Q

What are the different components of pain that analgesics act on?

A

Transduction

Transmission

Perception

Descending modulation

96
Q

What are some examples of analgesics?

A
  • Transduction
    • NSAIDs
    • Ice
    • Rest
    • LA blocks
  • Transmission
    • Nerve blocks
    • Drugs
      • Opioids
      • Anticonvulsants
    • Surgery
      • DREZ
      • Cordotomy
  • Perception
    • Education
    • Cognitive behavioural theory
    • Distraction
    • Relaxation
    • Graded motor imagery
    • Mirror box therapy
  • Descending modulation
    • Placebos
    • Drugs
      • Opioids
      • Antidepressants
    • Surgery
      • Spinal cord stimulation
97
Q

What are some different analgesics for the transduction component of pain?

A
  • NSAIDs
  • Ice
  • Rest
  • LA blocks
98
Q

What are some different analgesics for the transmission component of pain?

A
  • Nerve blocks
  • Drugs
    • Opioids
    • Anticonvulsants
  • Surgery
    • DREZ
    • Cordotomy
99
Q

What are some different analgesics for the perception component of pain?

A
  • Education
  • Cognitive behavioural theory
  • Distraction
  • Relaxation
  • Graded motor imagery
  • Mirror box therapy
100
Q

What are some analgesics for the descending modulation component of pain?

A
  • Placebos
  • Drugs
    • Opioids
    • Antidepressants
  • Surgery
    • Spinal cord stimulation

6. Neurology (Med) (47 decks)

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