230 - Pain Flashcards
What defines chronic pain?
> 6 months pain - as this is longer than natural healing processes
What is chronic pain syndrome?
Chronic pain + additional issues: depression, sleep issues, anxiety
What occurs in the chronic pain cycle?
Pain - fear of movement - avoidance - rest - distress + frustration - physically deconditioned - pain
How can you asses pain?
Use IMPACT guidelines
- Pain intensity
- Physical function
- Emotional function
- Rating of improvement
What is the difference between acute and chronic pain?
Acute - always a cause - aim to find cause and cure damage using a medical model
Chronic - no longer a clear cause - the pain has no function
What are the 2 types of pain?
Nociceptive - stimulus - pain pathway
Neuropathic - doesn’t need nociceptive stimulus, generalised within nervous system.
What is a nocicepter?
A receptor in a reflex arc + pathway
- the free nerve endings of a sensory nerve, can be speciallised to feel particular stimuli
- Thermal (TRPV1 receptor)
- Chemical (Histamines + bradykinin mediated)
- Mechanical (stretch receptors)
What are the 2 types of sensory nerve fibres involved in pain?
A-delta: myelinated, fast pain sensation, unimodal
C fibres: Unmyelinated, slow lingering pain, polymodal
(A-beta fibres inhibit nociceptive transmission)
How does inflammation affect pain?
Contributes to nociceptive pain - as inflammatory mediators sensitise nociceptive pathways - makes 1st order neurones more likely to fire.
- so use anti-inflams in pain drug therapy (eg. aspirin inhibits prostaglandins)
Describe the path that pain takes up the pain pathway
Pain sensed by a 1st order nocicepter, travels into the spinal cord. It synapses there with 2nd order neurone, ascends the spinothalamic tract to the thalamus. In the thalamus it synapses with a 3rd order neurone which forms the thalamocortical projection
- ends in:
- insula + cingulate cortex (makes pain unpleasant)
- Primary somatosensory cortex at post-central gyrus (localises pain - homunculus)
What is the role of the descending pathway in nociception?
Where does it project from?
It modulates the ascending pathway
Mediates endogenous analgesia - by giving microinjections of opioids.
Projects from 3 places:
- PAG (in midbrain) - opiodergic
- Nucleus of Raphe magnus - serapheneric and opiodergic
- Locus Coernelus - noradrenergic
Describe the endogenous opioid system
Gives endogenous pain relief
Has 3 receptors - Mu (addictive), Delta and Kappa
They are all metabotropic and G-protein coupled.
The endogenous opioids are all peptides:
- endorphins
- Enkephalins
- Dynorphins
As well as pain relief you get euphoria, sedation, cough suppression, respiratory depression. You can become tolerant.
How does the opioid system modulate pain?
Spinal interneurones release enkephalins into the synapse of 1st or 2nd order nociceptor neurones, which shuts down their activity.
The interneurones are activated by the descending pathway
What is neuropathic pain?
Pain caused by neuronal damage, eg. inflammation.
It sensitises nociceptive pathways - pain more readily transmitted.
What is hyperalgesia?
Pain hurts more than it should