Lecture 7: pain and nociception 2

Question 1

Dorsal horn neurons

Answer 1

nociceptive specific and wide dynamic range neurons play a key role in pain

Question 2

Neurogenic pain

Answer 2

• damaged nerves may create new receptors
• felt as noci activity from periphery
• new receptors may be sensitive to adrenaline released by SNS= sympathetically maintained pain
• analgesics < anti-depressants and anticonvulsants

Question 3

Referred pain

Answer 3

• explained by convergence of nociceptive info from various sources
• noci fibres converge on same ascending neuron- either in SC or thalamus

Question 4

Nociception outputs

Answer 4

1. SNS
2. Endocrine system
3. MSK system
4. Neurological descending pain modulation
5. Supraspinal changes

Question 5

SNS output

Answer 5

• Fight or flight response
• Normally supresses pain
• Releases noradrenaline
• Inhibits inflam response in short term

Question 6

Endocrine output

Answer 6

• Cortisol production increases in response to pain/stress
• > > release of energy
• &laquo_space;inflamm process
• Useful acutely, but delayed or poor healing may occur if maintained

Question 7

MSK output

Answer 7

• Noci can generate protective movement
• reflexes, antalgic postures and patterns
• reflex muscle spasms associated with chronic pain, although emotional/psycho states also impact

Question 8

Neuro response- descending pain inhibition

Answer 8

• inhibition of noci messages at dorsal horn via descending nerves

Question 9

Supraspinal plasticity

Answer 9

changes in cortical map

Question 10

Use of gate theory in pain management

Answer 10

• 1st order neurons converge onto common 2nd order
• Activity of primary afferents determines patterns of signal transmitted by 2nd order
• if mechanical afferent activity > noci activity, noci transmission is inhibited

Question 11

Counter-irritant theory at Dorsal Horn

Answer 11

• mechanical afferents stimulate interneurons&raquo_space; endorphins/natural opioids released
• these bind with primary afferents and interneurons of noci pathways
• decreased release of substance P
• inhibition of noci transmission results

Question 12

A-beta afferent system of descending anti-noci

Answer 12

• mechanoreceptive aff neurons eventually project to centres for descending inhib systems of brain and brainstem
• descending serotonergic pathway (opioid) and noradrenergic pathway (GABA) terminate in dorsal horn

Question 13

Pain pharmacology

Answer 13

• some can produce endorphins- can block noci transmission at DH
• Opiates bind to same receptors as endorphins to block noci pathways
• Multiple opiate receptors in CNS

Question 14

Descending pain modulation

Answer 14

• Serotonergic pathway- opioids- serotonin etc.
• Noradrenergic pathway- GABA- inhib amino acid
• modulate noci transmission
• fast pathways

Question 15

Stress on pain

Answer 15

• initially stims hormonal endorphin release
• hormones bind to opiate receptors = anti-noci
• long-term stress has opposite effect = pro-noc