Opioids Flashcards
How is pain stimulated?
Nociceptors stimulated Release of substance P and glutamate Afferent nerve stimulated Fibres decussate Action potential ascends Synapse in thalamus Project to post central gyrus
Name 2 specific pain afferent nerve fibres
A Delta fibre
C fibres
What pain do A delta fibres transmit
Sharp pain, myelinated
What pain do C fibres transmit?
Dull achey pain
Slower transmission
Which of the 2 types of pain afferent fibres need the higher stimulus
c fibres
Which specific parts of the dorsal horn do the 1st order synapse at?
Lamina 1 and 5
Which tract do the 2nd order neurones pass through?
Ascending lateral spinothalamic tract
Where does the 2nd order neurone synapse?
Thalamus
Where do 3rd order neurones synapse?
Pre-central gyrus
What is the key pain modulator in the peripheral system?
Substantia gelatinosa
What is the key pain modulator in the central system?
Peri-aqueductal grey
Describe the stimulatory pathway in peripheral pain?
Stimulator alpha and c fibres from damaged tissue to lamina 1 in dorsal horn then to the thalamus
Describe the inhibitory pathway in the peripheral pain
Inhibitory afferents towards substantial gelatinosa
How does ‘rub it better’ work?
Stimulates substantia gelatinosa, inhibiting lamina 1 and 5
How do we modulate pain centrally?
Pain afferents from dorsal horn to the thalamus, then stimulator paths to the cortex from then inhibitory stimulus to periaqueductal grey matter,
Give examples of endogenous opioids
Enkpehalins
Gynorphins
Beta-endorphins
Seratonin
What part do the endogenous opioids have on central pain modulation?
Inhibition from periaquaductal grey matter to dorsal horn
How are endogenous opioids categorised?
According to the class of GPCR receptors
What are the 3 classes of opioid receptors?
MOP
DOP
KOP
Where are MOP receptors found?
Supraspinal
GI tract
Where are DOP receptors found?
Wide distribution
Where are KOP receptors found?
Spinal cord
Brain
Periphery
What affect does all the endogenous opioids have on cAMP
Decreases it
What effect does MOP receptors have on minerals?
Outward flux of potassium
What effect does DOP receptors have on minerals?
Influx od calcium
What effect does KOP receptors have on minerals?
Efflux od potassium
Influx of calcium
What are the examples of MOP opioids?
Enkephalins
Beta endorphins
What are the examples of DOP opioids?
Enkephalins
What are the examples of KOP opioids?
Dynorphins
What is the order of the WHO analgesic ladder?
Simple analgesia- paracetamol NSAIDs
- -> Weak opioids-codeine
- -> Strong opioid- morphine, fentanyl
If the pain is neuropathic which analgesics are used preferentially?
Anticonvulsants
Tricyclics
Serotonin/NA reuptake inhibitors
What is the main receptor subtype with therapeutic effects?
MOP
What are uses od opioids?
Mainly to modulate pain
Cough
Diarrhoea
Palliation