Pain Flashcards
(28 cards)
What is analgesia?
Reduction/absence in pain
What is hyperalgesia?
Increased sensitivity to painful stimuli
What is allodynia?
Pain in response to non noxious stimuli
What is neuralgia?
Neural pain without stimulation of nociceptors
What is the pain pathway?
*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
What two types of nerve fibres are responsible for nociception in the periphery?
aDelta and C fibres
aDelta fibres thick diameter= faster electrical impulse transmission
aDelta slightly myelinated
What type of pain is felt through aDelta fibres?
Sharp fast localised prickly pain
What type of pain is felt through C fibres?
Dull slow throbbing
What is the role of the thalamus ?
*relays info between cerebral cortex and sub cortical centres
*regulates sleep
What is the pathway of the neospinothalamic tract?
- 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 - Ascends up to primary somatosensory cortex in brain to be processed
What is the pathway of the paleaospinothalamic pathway?
- 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 - Most neurones decussate via anterior white commissure
- Bilateral transmission because some neurones don’t decussate
- Bilateral transmission to thalamus to be relayed to hypothalamus, basal ganglia and SENSORY cortex
Why are there two sequential pain sensations after a single stimulus?
Due to
1st rapid- adelta fibres
2nd slow- C fibres
Pain experienced seconds apart
What needs inhibited to cause analgesia?
Substantia gelatinosa - inhibits signal transduction
What is gate control?
*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
How is pain inhibited by using opioids?
*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
What is pain?
An unpleasant sensory and emotional experience associated with or resembling that associated with actual or potential tissue damage
What is the purpose of acute pain?
Protective function
Warn of damage
Provokes movement away from harmful stimulus
What is the purpose of chronic pain?
Experienced once damage is already underway eg rheumatoid arthritis
What are the three steps of the WHO analgesic ladder for cancer and other chronic pain?
*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
How long after taking paracetamol do you feel the effect?
30-60 mins
How many grams of paracetamol per day would cause death?
10-12g
What are the benefits of using NSAIDs ie inhibition of COX?
Decrease inflammation- inhibit production of PGE2 and PGI2
What are the harmful side effects of inhibiting COX?
*gastric mucosa effects- PGE2 and PGI2
*renal function- PGE2
*platelet function- TXA2
*uterine contraction- PGF2
What patients are at risk from NSAID inducted GI side effects?
*history of GI issues
*>65years
*also using corticosteroids and or anticoagulants
*smoking
*alcohol
