Gate control theory of pain Flashcards
3 significances of pain
- forces to rest and so heal
- warning
- modifies avoidance behaviour
why does rubbing an injury decrease pain perception?
rubbing stimulates A delta fibres which opens the gate
How do we know descending pathways from the Brain Stem exist?
stimulation of PAG, PVG and raphe nuclei produced analgesia
Where are the raphe nuclei?
The medulla
What are the two main ascending pathways involved in pain?
spinoparabrachial and spinothalamic
what is the route for spinoparabrachial?
superficial dorsal horn to brain areas concerned with affect
how is the spinothalamic pathway involved in pain?
it distributes nociceptive info to areas of the cortex concerned with affect And discrimination
which neurons do drugs activate and why?
PAG neurons because it has a high density of opiate receptors (mew not k at brainstem level)
what were the first two discovered endogenous opiates?
met-enkephalin and leu-enkephalin (endorphins and dynorphins since discovered)
which factors regulate the gate?
- amount of activity in pain fibres
- amount of activity in other fibres ex. A delta
- Descending messages such as emotions and mental conditions
Is glutamate or substance p involved in faster pain transmission?
Glutamate is fast transmission
what % of amputees suffer from phantom limb pain?
80%
what is included in the “raphe system”?
the raphe nucleus and the medullary reticular formation
Which NT is released by the lateral spinal cord route path for descending pathways of pain inhibition?
NA, which acts mainly on enkephalin receptors
Which NT is released by the dorsolateral spinal cord route path for descending pathways of pain inhibition?
serotonin, which acts mainly on enkephalin receptors
What is the evidence for serotonergic systems in descending pain pathways?
- Inhibition of 5HT synthesis/destruction of cells that produce 5HT blocks analgesic action of opiates
- Applying 5HT to the spinal cord results in analgesia plus reduces response to noxious stimuli
What is the evidence for noradrenergic systems in descending pain pathways?
- morphine action blocked by alpha-adrenergic antagonists
2. NA to spinal cord induces analgesia
What evidence is against the role of NA systems in descending pain pathways?
Blocking NA in the RVM still allows analgesia
main potential function of facilitatory descending pathways
increase sensitivity to noxious stimuli during illness to promote recovery
