Opioid Analgesics Flashcards
Pain
Pain is a subjective experience
It is a direct response to an untoward event
Nociception
Nociception is the perception of noxious stimuli
It is not influenced by emotional factors
Nociceptive afferent pathway
Carries stimuli from the periphery to the CNS
- C-fibres = unmyelinated, have a relatively slow conductance rate & convey dull, burning pain
- Ad fibres = myelinated, have a relatively rapid conductance rate & convey sharp, localised pain
These peripheral neurons then synapse at the dorsal horn, where glutamate is released, taking the action potential to various areas of the brain
Descending inhibitory controls
These controls travel from the brain to the periphery in response to pain
They dampen ascending nociception by stimulation GABA(A) and Gi/o rerceptors
Primarily 5-HT neurons
Opioid function
Opioids inhibit transmission up the ascending pathway and enhance endogenous analgesic mechanisms
Opioid receptors
There are four opioid receptors
- u
- d
- k
- ORL
They are all Gi/o coupled and their endogenoius ligands are endorphins
u receptors
Provide analgesia of the supraspinal, spinal and peripheral areas
Found in the dorsal horn and on peripheral nociceptor neurons
May also cause respiratory depression, pupil constriction, euphoria and sedation
Activation hyperpolarises the neuron, limiting transmission of nociception
Morphine
An example of an opioid analgesic
Mirrors the effect of endogenous endorphins by acting as u agonists
Tolerance
Many opioids cause tolerance
A greater dose is then required to produce the same effect
This shortens the therapeutic window, increasing toxicity
Due to the desensitisation of u receptors
Physical dependence
Many opioids cause dependence
Withdrawal causes adverse physiological effects
Include drugs such as codeine and tramadol
