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A PA20023 > Pain, Nociception and analgesia > Flashcards

Pain, Nociception and analgesia Flashcards

1
Q

Define pain

A
  1. the subjective conscious appreciation of a stimulus that is causing, or threatening to cause, tissue damage
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2
Q

Define nociception

A
  1. the physical process of detection and transmission of damaging or potentially damaging (noxious) stimuli
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3
Q

What are Nociceptors

A
  1. Structures which detect noxious stimuli
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4
Q

What is algesia

A
  1. the induction of a condition leading to nociception and pain
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5
Q

What is analgesia

A
  1. reduction or prevention of either nociception or pain without loss of consciousness
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6
Q

What are two types of nociceptors

A
  1. polymodal nociceptors

2. mechanical nociceptors

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7
Q

What are polymodal nociceptors

A
  1. high intensity mechanical
  2. thermal - (> 45oC, <10oC)
  3. Chemical
  4. unmyelinated
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8
Q

What are mechanical nociceptors

A
  1. high intensity mechanical

2. strong thermal- (> 60oC)

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9
Q

What are the specialised nociceptors on end of nerve ending

A
  1. ASIC-
  2. P2X3
  3. VGNa
  4. VR-1/TRPV-1/Vanilloid 1
  5. All lead to depolarisation
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10
Q

What is agonist of ASIC

A
  1. Agonist is acid
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11
Q

What is P2X3

A
  1. Purinergic receptor
  2. Agonist is ATP
  3. Mechanical stimulation
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12
Q

What are agonists of VR-1/TRPV-1/Vanilloid 1

A
  1. Acid
  2. Heat
  3. Capsaicin- chilis
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13
Q

What is the difference between nociception and sensory transmission

A
  1. They conduct at slower velocities
  2. Nociceptors have different thresholds of activation
  3. They have different sites of projection into the spinal cord
  4. They elicit different physiological responses in dorsal horn neurons
  5. Information ascends in different pathways
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14
Q

What are different types of pain fibres

A
  1. A delta- sharp pricking pain
    a) Well tolerated
    b) Fast pain
    3 C fiber
    a) Slow pain
    b) Burning aching, throbbing
    c) Poorly tolerated
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15
Q

Describe Somatosensory transmission

A
  1. Comes in through dorsal route
  2. Nearly all noicreceptive input is at very most dorsal aspect of spinal cord
  3. Lamina 1 and 2- substantia gelantisosa
  4. Nearly all input from nociceptive neurons project
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16
Q

Describe ascending pathway

A
  1. Stimulus- injury
  2. Activates nociceptors
  3. Generates action potential
  4. Synapse in lamina 1 and 2
  5. Activates post synaptic receptors
  6. Crosses to other side of cord- ascending pathway
  7. Goes up to brain- thalamus
  8. Need input to somatosensory cortex so we know which part of body is affected
  9. Cingulate and insular do emotional responses to pain – why we feel miserable, but also helps us not to do painful things again – to instil a powerful emotional memory.
17
Q

What is referred pain

A
  1. Perceive pain in parts where damage isn’t
  2. Not good at determining where stimulus is coming from
  3. Oesophagus acid called heart burn
  4. Heart attack- feel it in left arm
  5. Don’t’ have enough space in somatosensory cortex to have input from all organs
  6. So different nociceptors that provide input to CNS from different parts of body converge at same second order neuron
  7. Our brain perceives what ever bit of skin that activates the neuron
18
Q

What is Hyperalgesia

A
  1. Increased response to a noxious stimulus
  2. Something happens to a part of your body that would normally be detected as pain but when in state of hyperalgesia the perception is bigger
19
Q

What is Allodynia

A
  1. Painful responses to a non-noxious stimulus
  2. Normally non-noxious stimulus becomes painful
  3. Burnt hand-
  4. Damaged part of body is sensitized
  5. Touching damaged part will cause pain
20
Q

What sites are affected by allodynia and hyperalgesia

A
  1. Increased sensitivity of peripheral nociceptors

2. Increased transmission in spinal cord

21
Q

Increased sensitivity of peripheral nociceptors

A
  1. Damage and leaky blood vessel walls leak out high K and ATP and H+,
  2. K directly depolarises things by changing the equilibrium potential or by acting directly onto,
  3. ATP acts directly on P2X3 receptors,
  4. H+ act on the ASIC channel
  5. Nociceptors – P2X3 and ASIC- Cause action potential generation
  6. The others are involved in inflammatory response
  7. Allow part of body to heal
  8. Bradykinin
  9. prostaglandin
  10. NGF
22
Q

What does substance P do

A
  1. Substance P - Blood vessels contract, and cause them to contract and become leaky – release stuff
  2. Also activate and recruit mast cell
  3. Release histamine
  4. Make vessels even more leaky
23
Q

Describe modulation of nociception

A
  1. NGF (nerve growth factor) activates TrkA
  2. TrkA sensitises nociceptors - Lowers threshold for them to open
  3. Bradykinin 2 receptors - Sensitises VR-1 channel
  4. Histamine H1 receptors - Sensitise VR-1
  5. Prostanoid receptor- activated by prostaglandins, Sensitises VGNa
  6. bradykinin also sensitIses VGNA
  7. Protect hurt parts of body
  8. But can go wrong- Rheumatoid arthritis
  9. Parts of body always inflamed nociceptor’s always sensitised
  10. Allodynia
24
Q

Describe cause of itch

A
  1. Afferent input is via Aδ and C fibres from free nerve endings- like nociceptive input
  2. Inflammation, particularly histamine, can cause it
  3. BUT Analgesics don’t inhibit itch- Opiates can cause itch
  4. To cure an itch, you scratch it (mechanical, almost nociceptive stimulation)
  5. Strong central component
  6. Capsaicin can relieve itch

A PA20023 (19 decks)

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