Opioids Flashcards
Effects of morphine
analgesia, constipation, tolerance, dependence, euphoria, anti-tussive
What does naloxone do?
block effects of opioids
Describe opioid receptors
(u,g,k )
7 transmembrane spanning receptors attached to Gi or Go.
How do opioid receptors work
inhib adenylate cyclase and decrease camp
causes K+ channels to open (K+ out) and Ca2+ channels to close
hyperpolarisation of membrane = presynaptic inhibition
they can also be post synaptic
How do you become tolerant to opoids
the G protein uncouples from the binding site so when opioids bind the ability to activate is reduced
Where are the vast majority of opioid receptors and why?
superficial lamina of the dorsal horn. as increased C fibres
How does morphine stop pain but keep the sense of touch
only on C fibres in superficial lamina, A fibres which are touch are in 3+4 of dorsal horn
% of opioid receptors pre and post synaptic
70 and 30
Describe how the spinal cord can override pain
Nucleus Raphe Magnus inhibits the spinal cord using GABA neurones
Describe how opioids affect descending inhibitory control of pain
opiod receptors are on PAG. These inhibit PAG–gaba–>NRM
inhibiting the GABA causes increased APs fired from NRM –gaba–>spinal cord
Why dont opioids work in chronic allodynia
as only on C fibres receptors allodynia is A fibres becoming painful
onset of opioid duration in
- iv
- im
- oral
- 2 min
- 20 min
- 1 hr
What is diamorphine and why is it so potent
heroin. high lipophilicity so the brain is penetrated rapid
3 positives to the use of codine
no addiction. less resp depression. good antitussive
when are pethidine and dentanyl used
labour , anasthesia
