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

Physiology of pain 1 Flashcards

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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

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

Path of third-order neurons in spinothalamic tract

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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

Study These Flashcards
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

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A
  • Periaqueductal gray matter(PAG)

- Rostral ventromedial medulla(RVM)

25
Purpose of the descending regulation of pain pathway
- Modulates activity of spinothalamic tract
26
How is pain inhibited by the action of the descending regulation of pain pathway
- 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
Where do serotonergic projections act in the descending pain regulation pathway
- Act on dorsal horn inhibitory interneurons
28
Role of opioids in the descending inhibition of pain
- Opiods are inhibitory | - Act on inhibitory metabotropic receptors
29
Where are opioids released
Released from interneurons at multiple sites - Midbrain(Periaqueductal gray matter) - Medulla(Rostral ventromedial medulla) - Dorsal horn
30
Effect of ATP on nociceptors
- ATP binds to purinergic receptors(P2X)
31
Effect of H+ on nociceptors
- Activates acid-sensing ion channels by binding to them
32
Effect of serotonin on nociceptors
- Binds to 5-HT3 receptors(activation)
33
What does switching nociceptors cause and give an example
- Switch on = PAIN | - In runners, lactic acid build up leads to tissue acidosis(increase in protons) = activation of nociceptors = PAIN
34
What is neurogenic inflammation
- Inflammation arising from the local release by afferent neurons of inflammatory mediators
35
Process of neurogenic inflammation
- 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
Causes of histamine release in neurogenic inflammation
- Vasodilation - Increased permeability - Activation of mast cells
37
What is an effect of inflammation that helps with repair
- 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
What is allodynia
- Non-noxious stimuli produce a painful response
39
What is hyperalgesia
- Noxious stimuli produce an exaggerated pain response
40
What is peripheral sensitization
- Increase in responsiveness of the peripheral ends of nociceptors
41
What is peripheral sensitisation driven by
- 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
Common example of peripheral sensitisation
- Sunburn
43
Mechanism of action - TRPV1
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
TRPV1 agonist and temp
- Chilli(capsaicin) | - HOT
45
TRPM agonist and temp
- Menthol | - Cold
46
TRPA1 agonist and temp
- Cinnamon | - V Cold
47
What do first order neurons in the spinothalamic tract release to excite second-order neurons
- Glutamate and substance P to excite second-order neurons
48
Cortex for lower body projections in spinothalamic tract
- Medial somatosensory cortex
49
Cortex for upper body projections in spinothalamic tract
- Lateral somatosensory cortex
50
How does descending regulation of pain occur
- Stress-induced analgesia | - eg: battle victims with no pain
51
Inhibition of pain pathway from RVM to dorsal horn
RVM --serotonergic neuron --> inhibitory interneuron --> nociceptor in dorsal horn

Year 2 - Theme 2 (14 decks)

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