Physiology Of Pain 2

Question 1

NSAIDs (aspirin, ibuprofen) act where and what is their mechanism of action?

Answer 1

Inhibit prostaglandin synthesis by inhibition of COX enzymes

And therefore this prevents the decrease in Na channel threshold

Question 2

Is paracetamol an NSAID?

Answer 2

Not anti inflammatory properties and acts centrally

Question 3

How does paracetamol work?

Answer 3

Activates descending seretonergic pathway

Question 4

Capsaicin treatment?

Answer 4

TRPV1 agonist, holds channel open, calcium overload causing mitochondrial dysfunction.

Nociceptors stops working

Or keeping channel open and depleting substance P

Question 5

How many people are affected by chronic pain?

Answer 5

20 to 50%

Question 6

Traction?

Answer 6

Nerves are stretched

Question 7

How many people affected by neuropathic pain?

Answer 7

8%

Question 8

Central sensitisation within spinal cord?

Answer 8

Increase responsiveness of spinothalamic tract neurons, reduced threshold for activation.

Constant firing of axons causes sustain release of glutamate and substance P, prolonged depolarisation. Influx of calcium in NMDA recptors activates kinases leading to phosphorylation of NMDA and AMPA.

This alters kinetics of channels and causes insertion of more channels. neurons fire more easily

Question 9

How to treat chronic pain?

Answer 9

Tricyclics antidepressants, anticonvulsants- these do have analgesic properties.

Question 10

Tricyclics antidepressants examples?

Answer 10

Amitriptyline and duloxetine- act centrally

Question 11

Tricyclics antidepressants mechanism?

Answer 11

Acts on descending inhibitory pathway preventing uptake of serotonin and noradrenalin

So constant inhibition of spinothalamic neurons by inhibitory interneurons

Question 12

Anticonvulsant examples?

Answer 12

Pregabalin, gabapentin and carbamazepine

Question 13

Anticonvulsants mechanism of action?

Answer 13

Reduce excitability in spinal cord, blocks calcium (pregabalin)and sodium channels (carbamazepine)

Nociceptors would activate spinothalamic neurons. But pregabalin blocks presynaptic voltage gated ca channels, preventing release of glutamate

Question 14

How do placebo work?

Answer 14

Activation of descending inhibitory pathway

Question 15

Acute and chronic pain duration?

Answer 15

Acute- less than 3 months

Chronic- more than 3 months

Question 16

How does lidocaine and lignocaine work?

Answer 16

By blocking sodium channels

Question 17

Gate control theory?

Answer 17

Stimulate ion of Abeta fibres activate interneurons which inhibit spinothalamic neurons

Question 18

What causes allodynia?

Answer 18

Non- noxious AB fibres also synapse onto 2nd order neurons, which are normally non-functional.

But now can activate sensitised 2nd order neurons.

Question 19

What is 3rd line treatment for neuropathic pain?

Answer 19

Specialist- oral tramodol or in combination with second line treatment topical lidocaine

Question 20

What is first line treatment for neuropathic pain?

Answer 20

Amitrriptyline, duloxetine, pregabalin and gabapentin

Second line would be switch drugs or combine

Question 21

What goes wrong in chronic pain?

Answer 21

Peripheral terminals- peripheral sensitisation

Axon- increased firing at primary afferent neurons

Dorsal root ganglia- changes in protein synthesis

Dorsal horn/spinal cord- central sensitisation

Brain- changes in brain activation patterns