Pain Flashcards
How do nociception and pain differ?
Pain is the subjective experience associated with nociception but also arising without a stimulus
Nociception is a neurophysiological term denoting a specific activity in neural pathways
What are nociceptors? What different types exist?
Afferent fibres and free nerve endings
Respond to force, heat, cold, chemicals - only above a certain higher than normal threshold when tissue damage is occurring.
May be polymodal or specific
- Alpha delta - myelinated, fast pain, some temperature specific, used for reflex responses
- C fibres - unmyelinated, slow pain, usually polymodal
- Alpha beta - non-nociceptive but will carry nociceptive signals sometimes, conduct most quickly
How may drugs affect nociceptors?
Different drugs act more potently on different fibres hence why some drug are better at alleviating some types of pain
eg. Opioids block C fibres, therefore are not good at blocking temperature.
Which tracts are responsible for different aspects of pain?
Spinothalamic -> thalamus, brainstem, cortex = mociception
Spinoreticular = emotional aspect
How are the neurone structured within the spinal cord?
In the dorsal horn reed laminae (layers I-V)
All spinothalamic and spinoreticular tracts decussate upon entry to the spinal cord
This organisation is maintained into the somatosensory cortex allowing for localisation of pain
Where is the first site of pain modulation?
Spinal cord
Which nerve pathways are more widely studied?
Cutaneous rather than visceral - easier to study
How is pain adaptive?
Evolutionary advantage to avoiding dangerous stimuli
- more relevant to acute than chronic pain
Give examples of research in different species attempting to elucidate whether pain is felt
Sneddon - rainbow trout will move away from a noxious stimulus but how can we know if this is high order cognition or just a reflex?
Robert Elwood - Hermit crabs will tolerate higher pain thresholds if only a worse shell is on offer to move to - suggesting not a reflex but more cognitive
How may age affect pain processing?
David Mellor - steroid levels in neonatal lambs -> lack of “consciousness” up to 6 hours
Craig Johnson - age/pain responses
> foetus surgery/abortion - analgesia?
> Precocious v altricial species
Outline two theories of pain modulation?
> Gate control theory - non painful/noxious stimuli close the gate (PRESYNAPTIC INHIBITION) and stop noxious stimuli getting through eg. rubbing after bumping yourself or TENS machine
Descending inhibition - PAG (periaquiductal grey) in the midbrain and RVM (rostral ventromedial medulla) conain high number of ovoid receptors and endogenous opioids.
- descending pathways project to the dorsal horn and are monoaminergic, utilising NA and 5HT as NTs.
- Nucleus raphe magnus also important
What does MNT stand for?
Mechanical nociceptive threshold
Which area of the brain is associated with pain?
Not one single part - the pain matrix
Multiple parts of the brain shown on fMRI to play a role
- disputed because similar patterns are observed for loud/bright/otherwise salient stimuli as well as noxious, swell as watching others in pain
> more likely to be a “threat matrix” or saliency matrix indicating saliency or threat of harm
Is the cerebral cortex necessary for feeling pain?
Not necessarily - may be other areas involved n other species
What does injury lead to?
- release of inflammatory mediators -> hyperalgesia, allodynia
- descending (usually antinociceptive) pathways may become pronociceptive
What are the three types of pain?
Physiological/nociceptive - Useful! Pinkprick pain, protects from damaging stimuli. Stops when stimulus removed
Inflammatory and neuropathic = clinical pain
What is the most common form of chronic pain noted in animals?
Chronic pain noted more commonly in humans, but..
Osteoarthritis commonest
Which psychological factors play a role in chronic pain issues?
Catastrophising - expecting the worst, learned helplessness and inactivity, depression - perpetuates physical mechanisms of chronic pain
Fear of pain - avoiding activities that cause the pain, leads to ^ pain perception when event occurs
- illness behaviour and social culture also play a role
What are the risk factors for development of CPSP?
Chronic post surgical pain
- Younger people ^ risk
- Anxiety/depression problems
- Pre-op pain - upregulating pain pathways and making it harder to control pain peri- and post-op
What are the 7 options for pin management in animals?
Systemic analgesia eg. NSAIDS, opioids Local analgesia Change of practice - don't cause pain! Rest Physiotherapy Euthanasia
Is it always possible to give an analgesic?
Companion animal - yes
Farm animal - potentially not - pet/commercial/hobby farm?
> strict legislation due to drug residue/food chain issues
> PETS aswel as commercial
> drugs must have known maximum residue limit and withdrawal period
> zero tolerance list that they are not allowed at all
> Must be recorded in a book
[-> WELFARE IMPLICATIONS!]
When may change in practice be best effective?
Eg. keel bone fractures in laying hens - not practical to pharmacologically treat pain in individuals
Give an example of withdrawal periods that may put the farmer off of giving analgesia?
Analgesia -> milk withdrawal
Are horses a food producing animal?
YES unless passport signed to say they will never enter the food chain
- but equine passport system not robustly controlled
