Pain + Analgesia

Question 1

What is Nociceptive pain?

Answer 1

Acute pain.
- e.g. Pin prick, Visceral distension.

Question 2

What is Inflammatory pain?

Answer 2

Prolonged pain
- e.g. sunburn, inflamed wound.

Question 3

What is Pathological pain?

Answer 3

Pain with no protective function that results from abnormal nervous system function.
- e.g. neuropathic or dysfunctional.

Question 4

What type of pain is adaptive and has a high threshold?

Answer 4

Nociceptive pain

Adaptive: serves as warning system to minimise contact with damaging stimuli.

High Threshold: Only provoked by intense stimuli activating nociceptors.

Question 5

What type of pain causes hypersensitivity to noxious stimuli and allodynia (innocuous stimuli now elicit pain)

Answer 5

Inflammatory pain.
- Caused by activation of the immune system in injury, or infection.

Question 6

What type of receptors respond to low threshold stimuli?

Answer 6

Low Threshold Mechanoreceptors (LTMs)
- mediate touch, vibration and pressure.

Question 7

What type of receptors respond to High threshold stimuli?

Answer 7

Nociceptors.
- Information from High threshold nociceptor units can be perceived as painful but is subject to modulation.

Question 8

What are the two subtypes of Nociceptor neurons?

Answer 8

A Delta-fibres (“first” or “fast” pain intensity - pin pricks, stabbing)

C-fibres (Burning, throbbing, Cramping.)

Question 9

Where in the spinal cord do Primary afferent axons terminate?

Answer 9

Centrally in the dorsal horn of the spinal cord.

Question 10

Where do the Nociceptor C and A-Delta fibres terminate?

Answer 10

Superficially in laminae 1 and 2 (also 5 for A-Delta fibres)

Question 11

What kinds of fibres are involved in the Dorsal column medical lemniscal pathway?

Answer 11

A-Alpha and A-Beta Fibres

Decussation at the pyramid of the medulla.

Question 12

What kinds of fibres are involved in the Anterolateral system (Spinothalamic tract) ?

Answer 12

A-Delta and C Fibres.

Decussation at level of the cord at point of entry via Lissauer’s tract.

Question 13

Which analgesic acts at the site of injury by decreasing Nociceptor sensitisation in inflammation?

Answer 13

NSAIDs
- They do this primarily by blocking synthesis of prostaglandins

Question 14

Which Analgesic suppresses synaptic transmission of nociceptive signals in the dorsal horn of the signal cord?

Answer 14

Opioids

Question 15

Which analgesic reduces pain by activating (or potentiating) descending inhibitory controls?

Answer 15

Opioids

Question 16

Which Analgesic reduces nociception and pain by suppressing nerve conduction through blocking / inactivating voltage-gated sodium channels?

Answer 16

Local Anaesthetics, such as lidocaine

Question 17

Which Analgesic reduce nociception and pain by targeting ion channels upregulated in nerve damage?

Answer 17

Gabapentinoids.

Question 18

Which enzymes do NSAIDs inhibit to prevent accumulation of prostaglandins?

Answer 18

COX-1 and COX-2

Question 19

Where do Brain regions involved in pain perception (cortex, amygdala) and the spinomesencephalic pathway project to?

Answer 19

The Periaqueductal grey (PAG)

Question 20

What does the PAG do?

Answer 20

Involved in pain modulation
- The PAG contains neural circuits that can inhibit or facilitate the transmission of pain signals in the spinal cord and brainstem. Activation of certain areas within the PAG can lead to analgesia (pain relief), while inhibition can increase sensitivity to pain.

Question 21

Which areas in the spinal cord does the PAG influence to to reduce pain sensation?

Answer 21

The locus coeruleus - noradrenergic effects

The nucleus raphe magnus - Serotonergic effects

Overall the PAG is important in coordinating adaptive responses to various internal and external stimuli, including pain, threat, and emotional arousal, thereby contributing to the overall regulation of physiological and behavioural functions.

Question 22

Which receptors do opioids work on?

Answer 22

mainly bind to Mu-receptors.
Also:
- Delta-receptors
- Kappa-receptors

(The PAG also has opioid receptors - their activation disinhibits descending projection neurons)

Question 23

What type of receptors mediate Opioid action?

Answer 23

G protein-coupled opioid receptors.