Pain

Question 1

What is analgesia?

Answer 1

Reduction/absence in pain

Question 2

What is hyperalgesia?

Answer 2

Increased sensitivity to painful stimuli

Question 3

What is allodynia?

Answer 3

Pain in response to non noxious stimuli

Question 4

What is neuralgia?

Answer 4

Neural pain without stimulation of nociceptors

Question 5

What is the pain pathway?

Answer 5

*noxious stimuli to nociceptors at free nerve endings
*impulse passes through AFFERENT neurone towards CNS (sensory)
*through the dorsal root ganglion where the sensory neurone synapses in the dorsal horn (substantia gelatinosa)
*aDelta fibres release glutamate at synapse, C fibres release substance P
*processed in CNS
*if impulse needs to go to brain, goes via spinothalamic tracts (neospinothalamic (lateral ADelta fibres for fast pain), palaeospinothalamic (bilateral, c fibres for slow dull pain))
*reaction impulse travels away from CNS towards effector along EFFERENT neurone (motor)
*produces motor response

Question 6

What two types of nerve fibres are responsible for nociception in the periphery?

Answer 6

aDelta and C fibres
aDelta fibres thick diameter= faster electrical impulse transmission
aDelta slightly myelinated

Question 7

What type of pain is felt through aDelta fibres?

Answer 7

Sharp fast localised prickly pain

Question 8

What type of pain is felt through C fibres?

Answer 8

Dull slow throbbing

Question 9

What is the role of the thalamus ?

Answer 9

*relays info between cerebral cortex and sub cortical centres
*regulates sleep

Question 10

What is the pathway of the neospinothalamic tract?

Answer 10

1. Nociceptors stimulated. Travels up afferent aDelta fibre (1st order neurones)
   2.Via dorsal root ganglion
   3.enters spinal cord at dorsal horn, synapses via substantia gelatinosa- glutamate released
   4.2nd order neurone decissates via anterior white commissure to other side of spinal cord
2. Ascends up to primary somatosensory cortex in brain to be processed

Question 11

What is the pathway of the paleaospinothalamic pathway?

Answer 11

1. Nociceptors stimulated, impulse travels along afferent C fibres (1st order)
   2.Via dorsal root ganglion
   3.enters spinal cord via both dorsal and ventral horn
   4.1st order neurones synapse via substantia gelatinosa releasing substance P
2. Most neurones decussate via anterior white commissure
3. Bilateral transmission because some neurones don’t decussate
4. Bilateral transmission to thalamus to be relayed to hypothalamus, basal ganglia and SENSORY cortex

Question 12

Why are there two sequential pain sensations after a single stimulus?

Answer 12

Due to
1st rapid- adelta fibres
2nd slow- C fibres
Pain experienced seconds apart

Question 13

What needs inhibited to cause analgesia?

Answer 13

Substantia gelatinosa - inhibits signal transduction

Question 14

What is gate control?

Answer 14

*activation of Ab mechanoreceptors
*mechanoreceptors synapse onto spinothalamic tract
*inhibits transduction of impulse to sensory cortex
*sometimes there’s an inter neurone
*branched Ad fibres might lessen the inhibitory affect though

Question 15

How is pain inhibited by using opioids?

Answer 15

*ACTIVATION OF DESCENDING PATHWAY
*opioids activate periaqueductal grey
* which activates the nucleus raphe Magnus
*input descends via neuronal fibres which terminate in SUBSTANTIA GELATINOSA
*stops pain transduction
*analgesia

OR

*opioids act directly on substantia gelatinosa-inhibit
*ultimately inhibit release substance P

Question 16

What is pain?

Answer 16

An unpleasant sensory and emotional experience associated with or resembling that associated with actual or potential tissue damage

Question 17

What is the purpose of acute pain?

Answer 17

Protective function
Warn of damage
Provokes movement away from harmful stimulus

Question 18

What is the purpose of chronic pain?

Answer 18

Experienced once damage is already underway eg rheumatoid arthritis

Question 19

What are the three steps of the WHO analgesic ladder for cancer and other chronic pain?

Answer 19

*step 1- initial pain-non opioid +- adjuvants NSAIDS, paracetamol
*step 2- pain persists or increases- weak opioid + non opioid +- adjuvants- codeine
*step 3- severe pain or pain persisting or increasing- strong opioids + non opioid adjuvants- morphine

Question 20

How long after taking paracetamol do you feel the effect?

Answer 20

30-60 mins

Question 21

How many grams of paracetamol per day would cause death?

Answer 21

10-12g

Question 22

What are the benefits of using NSAIDs ie inhibition of COX?

Answer 22

Decrease inflammation- inhibit production of PGE2 and PGI2

Question 23

What are the harmful side effects of inhibiting COX?

Answer 23

*gastric mucosa effects- PGE2 and PGI2
*renal function- PGE2
*platelet function- TXA2
*uterine contraction- PGF2

Question 24

What patients are at risk from NSAID inducted GI side effects?

Answer 24

*history of GI issues
*>65years
*also using corticosteroids and or anticoagulants
*smoking
*alcohol

Question 25

What two NSAIDs have the highest cardiovascular risk and were withdrawn?

Answer 25

*Rofecoxib
*Valdecocib

Question 26

What is the cardiovascular risk with non selective NSAIDs?

Answer 26

*INCREASED RISK OF CV EVENTS
*naproxen lowest risk- safest from CV risk
*COX 2 selective inhibitors cause smaller increase in CV risk

Question 27

What NSAID has lowest GI side effects?

Answer 27

Ibuprofen

Question 28

When are NSAIDs contraindicated ?

Answer 28

Someone with peptic ulceration