S17+18 Pain

Question 1

How are nociceptors sensitised?

Answer 1

Tissue damage and inflammation triggers the release of prostaglandins, bradykinin and histamine.

Question 2

Which type of fibres carry nociceptive information?

Answer 2

Unmyelinated C fibres - polymodal.

Aδ fibres - thermal and mechanical.

Question 3

Differentiate between first and second pain.

Answer 3

1st: Aδ. Sharp, easily localised, rapid, short, mechanical/thermal.
2nd: C fibres. Dull ache, poorly localised, slow onset, persistent. Polymodal.

Question 4

What are the spinal connections of nociceptive axons?

Answer 4

Cell bodies in dorsal root ganglion. Up/down short distance in Zone of Lissauer. Synapse onto neurones in lamina I + II : substantia gelatinosa.

Question 5

Which neurotransmitters are used by pain afferents?

Answer 5

Glutamate.
Substance P (most dense in superficial dorsal horn, receptor: NK1).

Question 6

What are the three ascending pain pathways?

Answer 6

Lateral spinothalamic tract.
Spinoreticulothalamic tract.
Anterior spinothalamic tract.

Question 7

What is dissociated sensory loss?

Answer 7

Touch, kPa, vibration + proprioception lost on the same side.
Pain lost on opposite side.

Question 8

How is pain and temperature info carried from the face?

Answer 8

Trigeminal system. Small afferents descend in spinal trigeminal tract to brain stem. Synapse in pars caudalis, ascend contra laterally in trigeminothalamic tract. Projects via ventral posteromedial nucleus.

Question 9

What is the aetiology of phantom limb pain?

Answer 9

Cortical reorganisation of somatotopic representation in thalamus/cortex.
Central sensitisation - reduction of inhibitory processes in dorsal horn, sprouting of Aβ fibres into lamina I + II.

Question 10

Name two endocannabinoids.

What do they do?

Answer 10

Anandamide.
2-arachidonyl-glycerol.
Inhibits behaviour response to noxious stimuli, limits hyperalgesia and neuropathic pain.

Question 11

How do higher brain centres influence pain perception?

Answer 11

Descending pathways from periaqueductal grey and reticular formation decrease transmitter release from primary afferent terminals via opioid receptors.

Question 12

What are the two defining features of pathological pain?

Answer 12

Hyperalgesia (increased pain sensation).

Allodynia (touch-evoked pain).

Question 13

What is the gate theory of pain?

Answer 13

Co activation of mechanoreceptors (Aα/β fibres) with nociceptors with suppress activation of the projection neutron by C fibres.

Question 14

Name five factors associated with changes in pain perception.

Answer 14

Anxiety.
Depressed affect.
Gender.
Circadian variation.
Climatic conditions.

Question 15

How do NSAIDS act?

Side effects? (3)

Answer 15

COX inhibition, decrease in prostaglandin.

GI bleeds, renal toxicity, cardiovascular effects.

Question 16

How does paracetamol act?

Side effect?

Answer 16

Inhibition of prostaglandin synthesis.

Toxic liver damage.

Question 17

How do opioids work?

Side effects?

Answer 17

Activate endogenous analgesic system.

N+V, consitpation, dizziness, somnolence, dry skin.

Question 18

What are the side effects of systemic opioid analgesic use?

Warning sign?

Answer 18

Respiratory depression and hypoxia.

Progressive sedation.

Question 19

What are the mechanisms of neuropathic pain?

Answer 19

Hyper excitable spinal cord with new dorsal horn inputs.

Remapping of thalamus and cortex.

Question 20

What are features suggestive of neuropathic pain?

Answer 20

Different from normal pain.
In absence of tissue damage.
In area of sensory loss.
Allodynia, hyperalgaesia, dysthaesias.

Question 21

How is pain measured?

Answer 21

McGill Pain questionnaire.

Question 22

Which types of drugs are used for neuropathic pain?

Answer 22

Antidepressants (TCA's, SUIs).
Anticonvulsants.
Opioids.
Membrane stabilising drugs.
Topical drugs.

Question 23

How do tri-cyclic antidepressants work?

Side effects?

Answer 23

Inhibition of neuronal reuptake of noradrenaline and serotonin.
Constipation, dry mouth, somnolence, heart abnormalities, insomnia, increased appetite.

Question 24

Which anticonvulsants are used in neuropathic pain?

Answer 24

Carbamazepine, phenytoin (NA+ channel blockers - serious + troublesome side effects).
Valproate + clonazepam (GABA agonists).
Gabapentin.

Question 25

How does spinal cord stimulation work?

Answer 25

Electrodes stimulate release of endogenous chemicals that dampen down pain.