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Year 2 - Theme 2 > Physiology of pain 1 > Flashcards

Physiology of pain 1 Flashcards

1
Q

Definition of pain

A
  • Unpleasant sensory experience associated with tissue damage
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2
Q

Classification of pain

A

Nociceptive - normal functioning of nociceptors

Inflammatory - Pain in response to inflammation

Neuropathic - Pain in response to injury to the nervous system

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3
Q

What are nociceptors

A
  • Are primary sensory neurons that detect pain
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4
Q

Classification of sensory nerve fibres

A
  • alpha and beta fibres
  • A delta fibre
  • C fibre
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5
Q

Features of alpha and beta fibres

A
  • Myelinated
  • Large diameter
  • Light touch, proprioception
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6
Q

Features of A delta fibres

A
  • Thinly myelinated
  • Medium diameter
  • Light touch, temp, nociception
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7
Q

Features of C fibres

A
  • Unmyelinated
  • Small diameter
  • Temperature, nociception
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8
Q

What does it feel like when alpha delta fibres respond

A
  • Sharp pricking pain
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9
Q

What does it feel like when C fibres respond?

A
  • Slow dull ache

- Burning pain

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10
Q

Features of fast sharp pricking pain

A
  • Well localised

- Activation of reflex arcs

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11
Q

Localisation of slow dull aches

A
  • Poorly localised
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12
Q

Visceral pain and first response

A
  • Visceral pain has no response
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13
Q

What activates nociceptors

A
  • Pressure
  • Heat
  • Cold
  • Chemical
  • Tissue damage/inflammation
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14
Q

What is polymodality

A
  • Polymodality is the feature of a single receptor of responding to multiple modalities, such as free nerve endings which can respond to temperature, mechanical stimuli (touch, pressure, stretch) or pain (nociception)
  • Most C-fibre nociceptors are polymodal
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15
Q

How is pressure detected

A
  • Mechanically sensitive ion channels
  • Not yet identified in eukaryotic cells
  • Acid sensing ion channels
  • Transient receptor potential(TRP) family of channels
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16
Q

How is temperature detected

A
  • Transient receptor potential family of channels

- Detect different temperatures

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17
Q

Which tract does pain information ascend via

A
  • Spinothalamic tract
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18
Q

Where do first-order neurons enter and synapse in spinothalamic tract

A
  • Enter dorsal horn
  • Form tract of lissauer
  • Synapse in substantia gelatinosa
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19
Q

Path of second-order neurons in spinothalamic tract

A
  • Cross in dorsal horn at each level

- Ascend in anterolateral column to thalamus

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20
Q

How do we feel referred pain

A
  • Convergence of visceral and cutaneous nociceptors on same second order neurons in spinal cord
  • Brain perceives pain as cutaneous
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21
Q

Referred pain for angina

A
  • Angina perceived as pain in upper chest wall and left arm
22
Q

Path of third-order neurons in spinothalamic tract

A
  • Ascend to primary somatosensory cortex
  • Projections to insula and cingulate cortex
  • Encode the emotional components of pain(unpleasantness, negative-affect)
23
Q

What regions of the brain are activated in the pain network

A
  • Many cortical regions activated(including limbic system, prefrontal cortex)
24
Q

What are the two important regions of the descending regulation pathway of pain

A
  • Periaqueductal gray matter(PAG)

- Rostral ventromedial medulla(RVM)

25
Q

Purpose of the descending regulation of pain pathway

A
  • Modulates activity of spinothalamic tract
26
Q

How is pain inhibited by the action of the descending regulation of pain pathway

A
  • Cortical regions project to PAG
  • PAG projects to RVM
  • RVM projects to dorsal horn
  • PAG neurons excite RVM neurons, which inhibit(or excite) the spinothalamic tract
27
Q

Where do serotonergic projections act in the descending pain regulation pathway

A
  • Act on dorsal horn inhibitory interneurons
28
Q

Role of opioids in the descending inhibition of pain

A
  • Opiods are inhibitory

- Act on inhibitory metabotropic receptors

29
Q

Where are opioids released

A

Released from interneurons at multiple sites

  • Midbrain(Periaqueductal gray matter)
  • Medulla(Rostral ventromedial medulla)
  • Dorsal horn
30
Q

Effect of ATP on nociceptors

A
  • ATP binds to purinergic receptors(P2X)
31
Q

Effect of H+ on nociceptors

A
  • Activates acid-sensing ion channels by binding to them
32
Q

Effect of serotonin on nociceptors

A
  • Binds to 5-HT3 receptors(activation)
33
Q

What does switching nociceptors cause and give an example

A
  • Switch on = PAIN

- In runners, lactic acid build up leads to tissue acidosis(increase in protons) = activation of nociceptors = PAIN

34
Q

What is neurogenic inflammation

A
  • Inflammation arising from the local release by afferent neurons of inflammatory mediators
35
Q

Process of neurogenic inflammation

A
  • Activation of one branch of a nociceptor axon, triggers release of substance P and CGRP from another(leads to cascade)
  • Release of histamine causes more inflammation
36
Q

Causes of histamine release in neurogenic inflammation

A
  • Vasodilation
  • Increased permeability
  • Activation of mast cells
37
Q

What is an effect of inflammation that helps with repair

A
  • Inflammation can cause pain hypersensitivity

- Helps after an injury as it ensures that contact with the injured tissue is minimized until repair is complete

38
Q

What is allodynia

A
  • Non-noxious stimuli produce a painful response
39
Q

What is hyperalgesia

A
  • Noxious stimuli produce an exaggerated pain response
40
Q

What is peripheral sensitization

A
  • Increase in responsiveness of the peripheral ends of nociceptors
41
Q

What is peripheral sensitisation driven by

A
  • Driven by tissue injury or inflammation
  • Bradykinin and NGF reduce the threshold of heat activated channels(TRPV1)
  • Prostaglandin reduces the thresholds of sodium channels
42
Q

Common example of peripheral sensitisation

A
  • Sunburn
43
Q

Mechanism of action - TRPV1

A

Bradykinin

  • Binds to receptor(metabotropic - G protein-coupled)
  • Activation of protein kinase phosphorylates TRPV1
  • Phosphorylation of channel reduces its threshold(ie it fires more easily)
44
Q

TRPV1 agonist and temp

A
  • Chilli(capsaicin)

- HOT

45
Q

TRPM agonist and temp

A
  • Menthol

- Cold

46
Q

TRPA1 agonist and temp

A
  • Cinnamon

- V Cold

47
Q

What do first order neurons in the spinothalamic tract release to excite second-order neurons

A
  • Glutamate and substance P to excite second-order neurons
48
Q

Cortex for lower body projections in spinothalamic tract

A
  • Medial somatosensory cortex
49
Q

Cortex for upper body projections in spinothalamic tract

A
  • Lateral somatosensory cortex
50
Q

How does descending regulation of pain occur

A
  • Stress-induced analgesia

- eg: battle victims with no pain

51
Q

Inhibition of pain pathway from RVM to dorsal horn

A

RVM –serotonergic neuron –> inhibitory interneuron –> nociceptor in dorsal horn

Year 2 - Theme 2 (14 decks)

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