Pain Flashcards
(30 cards)
What is nociception?
sensory process that provides the signals that trigger pain
Where are nociceptors found?
in the periphery as simple free nerve endings
unmyelinated ‘c’ fibres and thinly myelinated ‘Ad’ fibres
comes from naked unmyelinated branch endings in the dermis
What chemicals are released during tissue damage and inflammation that interact with nociceptors and induce pain?
prostaglandins
bradykinin
histamine
How fast do the impulses travel in pain?
slow relative to other modalities
but there is both slow and fast pathways
Which nociceptors have ‘Ad’ fibres?
thermal
mechanical
Which nociceptors have ‘C’ fibres?
polymodal e.g. chemical, thermal and mechanical
What is first pain like and what fibres does it run through?
Fast
sharp/prickling
short
mechanical or thermal nociceptors = A-delta fibres
What is second pain like and what fibres does it run through?
Slow
dull ache/burning
persistent
polymodal nociceptors = C fibres
What is the substantia gelatinosa?
first order neurons of the spinothalamic tract synapse
principle areas innervated by nociceptor afferents
Why does referred pain happen?
Nociceptive afferents from internal organs e.g. viscera and the skin enter spinal cord through common routes
OVERLAPPING populations of spinal neurons.
visceral pain is perceived as having a cutaneous source by the sufferer
What are examples to referred pain in the body?
Oesophagus pain → chest wall heart → chest and arms Bladder → perineum Ureter → lower abdomen and back Prostate → lower trunk and legs Appendicitis → abdominal wall around naval (early stages)
What is the excitatory transmitter and neuropeptide in pain afferents?
glutamate
substance P
What is phantom pain?
Pain and touch sensations with no sensory inputs
Happens in amputees
Highly resistant to treatment
What is the perception of pain controlled by?
central modulation
What is hyperalgesia?
tissue that has already been damaged or inflamed is unusually sensitive
What is the difference between acute and chronic pain?
Acute - usually associated with trauma/injury, resolves quickly
Chronic - pain that persists beyond time of healing (3-6 months)
What is the WHO analgesia ladder?
start with non opioids e.g. NSAIDs, Paracetamol
Opiods for mild pain e.g. codeine, tramadol
Opiods for severe pain e.g. Morphine, Fentanyk, Methadone
What are NSAIDs mode of action?
inhibits cycleoxygenase
prostaglandin synthesis decreases
What are the side effects of NSAIDs?
GI irritation/bleeding
renal toxicity
drug-drug interactions
CV side effects
What is paracetamol’s mode of action?
inhibits central prostaglandin synthesis
What is the side effects of paracetamol?
risk of toxic liver damage
What are opioid analgesics mode of action?
activates endogenous analgesia system
stimulate receptors in limbic system - remove feeling of pain
affects descending pain pathways
reduces ascending pain signals
What are the side effects of opioid analgesics?
nausea vomiting constipation dizziness/vertigo somnolence - makes your sleepy dry skin respiratory depression/hypoxia - most serious effect
In renal failure what painkiller should be avoided?
morphine
codeine
