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Module 202 Neuroscience & behaviour > T2 L7 Physiology of pain > Flashcards

T2 L7 Physiology of pain Flashcards

1
Q

What is the definition of pain?

A

Unpleasant sensory experience accompanied by tissue damage

Accompanied with emotional reaction

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2
Q

Why do we feel pain?

A

Warning sign
Avoid harmful situations
Prevent further injury or death
Tells us to rest following injury

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3
Q

What are the different sensations of pain?

A 
Deep ache
Burning
Itchy
Stabbing
Freezing
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4
Q

What are the 3 classifications of pain?

A

Nociceptive
Inflammatory
Neuropathic

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5
Q

Describe Aa & Ab fibres

A

Myelinated
Large diameter
Light touch, proprioception
30-75nm/sec

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6
Q

Describe Aδ

A

Thinly myelinated
Medium diameter
Light touch, temperature, nociception
5-30nm/sec

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7
Q

Describe C fibres

A

Unmyelinated
Small diameter
Temperature, nociception
0.5-2nm/sec

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8
Q

What response do Aδ fibres produce?

A

Sharp pricking pain

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9
Q

What response do C fibres produce?

A

Slow, dull ache or burning pain

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10
Q

What can activate nociceptors?

A 
Pressure
Heat
Cold
Chemical
Tissue damage / inflammation
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11
Q

What do polymodal nociceptors respond to?

A

Pressure
Temperature
Chemical

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12
Q

Describe the transduction mechanism for pressure

A

Mechanically sensitive ion channel
Not yet identified in eukaryotic cells
Acid-sensing ion channels (ASIC)
Transient receptor potential (TRP) family of channels

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13
Q

Describe the transduction mechanism for temperature?

A

Transient receptor potential family of channels
6 transmembrane domains
Activated by aromatic agonists

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14
Q

What activates TRVP1?

A

Hot temperatures

Agonist is chilli (capsaicin)

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15
Q

Describe the central pain pathway in first order neurons

A

Enter dorsal horn
Form tract of Lissauer
Synapse in substantia gelatinosa
Glutamate & substance P excite second order neurons

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16
Q

Describe the central pain pathway in second order neurons

A

Cross in dorsal horn at each level

Ascend in anterolateral column to thalamus

17
Q

Describe why referred pain occurs

A

Convergence of visceral & cutaneous receptors on same second order neurons in spinal cord
Brain perceives pain as cutaneous

18
Q

Describe the central pain pathway in third order neurons

A

Ascend to primary somatosensory cortex
Encode sensory components e.g. where it hurts & modality
Projections to insula & cingulate cortex to encode emotional components of pain
Pain network

19
Q

What determines pain experience?

A

Behaviour
Emotions
Past experiences

20
Q

What are 2 important regions in the descending regulation of pain?

A

Periaqueductal grey matter

Rostral ventromedial medulla

21
Q

Describe the pathway from PAG to dorsal horn

A

Periaqueductal grey matter projects to rostral ventromedial medulla which projects to dorsal horn
Modulates activity of spinothalamic tract

22
Q

Describe the inhibition of pain

A

PAG neutrons excite RVM neutrons which inhibit or excite spinothalamic tract
Serotonergic projects act on dorsal horn inhibitory interneurons
Also parallel noradrenalin pathway

23
Q

Where are opioids released from?

A

Interneurons at multiple sites:

  • midbrain (periaqueductal grey matter)
  • medulla (rostral ventromedial medulla)
  • dorsal horn
24
Q

What do opioids act on?

A

Inhibitory metabotropic receptors

25
Q

What chemicals are released by tissue damage?

A 
ATP
H+
Serotonin
Histamine
Bradykinin
Prostaglandins
Nerve growth factor
26
Q

What does ATP bind to?

A

Purinergic receptors (P2X)

27
Q

What does H+ bind to?

A

Acid-sensing ion channels

28
Q

What does serotonin bind to in the activation of nociceptors?

A

5HT3 receptors

29
Q

What happens when lactic acid builds up?

A

1) Tissue acidosis
2) Increased H+
3) Activation of nociceptors
4) Pain

30
Q

What are the causes of neurogenic inflammation?

A

Vasodilation
Increased permeability
Activation of mast cells which release histamine causing more inflammation

31
Q

What is allodynia?

A

Non-noxious stimuli produces a painful response

32
Q

What is hyperalgesia?

A

Noxious stimuli produce exaggerated pain response

33
Q

What is the benefit of pain hypersensitivity from inflammation?

A

Pain is more painful

Helps healing by ensuring contact with injured tissue is minimised until repair is complete

34
Q

What are the mechanisms of pain hypersensitivity?

A

1) Peripheral sensitisation

2) Central sensitisation

35
Q

Describe peripheral sensitisation

A

Increase in responsiveness of peripheral ends of nociceptors
Driven by tissue injury or inflammation
Bradykinin & NGF –> reduce threshold of heat-activated channels.

36
Q

What happens when bradykinin binds to receptor?

A

Activation of protein kinase –> phosphorylates TRPV1 –> reduces its threshold –> fires more easily

37
Q

What does prostaglandin do?

A

Reduces threshold of sodium channels

Module 202 Neuroscience & behaviour (39 decks)

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