Pain, Nociception and analgesia

Question 1

Define pain

Answer 1

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

Question 2

Define nociception

Answer 2

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

Question 3

What are Nociceptors

Answer 3

1. Structures which detect noxious stimuli

Question 4

What is algesia

Answer 4

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

Question 5

What is analgesia

Answer 5

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

Question 6

What are two types of nociceptors

Answer 6

1. polymodal nociceptors

2. mechanical nociceptors

Question 7

What are polymodal nociceptors

Answer 7

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

Question 8

What are mechanical nociceptors

Answer 8

1. high intensity mechanical

2. strong thermal- (> 60oC)

Question 9

What are the specialised nociceptors on end of nerve ending

Answer 9

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

Question 10

What is agonist of ASIC

Answer 10

1. Agonist is acid

Question 11

What is P2X3

Answer 11

1. Purinergic receptor
2. Agonist is ATP
3. Mechanical stimulation

Question 12

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

Answer 12

1. Acid
2. Heat
3. Capsaicin- chilis

Question 13

What is the difference between nociception and sensory transmission

Answer 13

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

Question 14

What are different types of pain fibres

Answer 14

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

Question 15

Describe Somatosensory transmission

Answer 15

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

Question 16

Describe ascending pathway

Answer 16

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.

Question 17

What is referred pain

Answer 17

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

Question 18

What is Hyperalgesia

Answer 18

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

Question 19

What is Allodynia

Answer 19

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

Question 20

What sites are affected by allodynia and hyperalgesia

Answer 20

1. Increased sensitivity of peripheral nociceptors

2. Increased transmission in spinal cord

Question 21

Increased sensitivity of peripheral nociceptors

Answer 21

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

Question 22

What does substance P do

Answer 22

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

Question 23

Describe modulation of nociception

Answer 23

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

Question 24

Describe cause of itch

Answer 24

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