physiology and pathophysiology of pain Flashcards
what part of the brain does pain get transmitted to?
thalamus
what is nociception?
the detection of tissue damage by specialized transducers connected to A-delta and C fibres
what are nociceptors?
free nerve ending of A delta and C fibres
what do nociceptors respond to?
thermal,chemical, mechanical noxious stimuli
where do nociceptors synapse?
spinal cord
what type of pain are A delta fibres responsible for?
sharp or “first” pain
what type of pain are C fibres responsible for?
dull pain which comes after the initial sharp pain
what are the 3 types of neurons that are predominantly found in grey matter?
low threshold mechanoreceptive neurons
nociceptive specific neurons
wide dynamic range neurons
where do the spinothalamic tracts relay information to in the brain?
thalamus
what rexed areas does the spinothalamic tract arise from?
2 and 5
where does the LATERAL STT terminate?
ventroposterior thalamic nuclei
where do the ventroposterior thalamic nuclei feed to?
somatosensory cortex
where does the VENTRAL STT terminate?
medial thalamic nuclei
where do the medial thalamic nuclei project to?
limbic system
anterior cingulate cortex
insular cortex
where does pain perception occur?
somatosensory cortex
what is the lateral part of the pain matrix composed of?
somatosensory cortex
ventroposterior thalamic nuclei
what is the medial part of the pain matrix composed of?
amygdala hippocampus cingulate and prefrontal cortexes insula brainstem centres
what is the lateral part of the pain matrix involved in?
sensory discriminative part of nociception
what is the medial part of the pain matrix involved in?
affective and emotional components as well as descending control of pain
where are descending pathways located?
from the brain to the dorsal horn
what is the usual effect of descending pathways?
usually decrease pain signal
what kind of system are descending pathways?
noradrenergic system
what is hyperalgesia?
leftward shift of the stimulus response curve; increased perception of pain or perception of non noxious stimuli as noxious
when does hyperalgesia occur?
whenever there is tissue damage and inflammation?
what is primary hyperalgesia?
hyperalgesia at the site of injury
what is secondary hyperalgesia?
hyperalgesia in tissue surrounding the injury
what is allodynia?
dynamic mechanical hyperalgesia brought on by light touch
what changes occur in nociceptors in hyperalgesia?
exaggerated response to normal and supranormal stimuli
what is central sensitization?
response of second order neurons in the CNS to normal input which can be both noxious or non noxious
what are the 3 components of central sensitization?
wind up
classical
long term potentiation
what kind of synapses does the wind up phase of central sensitization involve?
only activated synapses
what effect does the wind up phase have on the neurons it affects?
progressively increases the response of the neurons
when does the wind up phase manifest?
only over the course of a stimulus and ends with the stimulus
what does the classic phase of central sens. involve?
opening of new synapses - new synapses start to receive input and record nociception
what is the wind up mechanism chemically mediated by?
substance P and CGRP
what receptor when activated by glutamate can trigger classical central sensitization?
NMDA
what is the clinical reuslt of classical central sensitization?
secondary hyperalgesia
how can classical central sens. be maintained after it has been activated?
low intensity of the offending stimuli
what are 2 types of central sensitization?
segmental
suprasegmental
what is nociceptive pain?
pain that occurs when specific peripheral sensory neurones respond to noxious stimuli
what are some features of nociceptive pain?
pain typically localised at site of injury
usually time limited and resolves when damaged tissue heals
tends to respond to conventional analgesics
what is neuropathic pain?
pain initiated or caused by a primary lesion or dysfunction in the somato sensory nervous system
what are some features of neuropathic pain?
painful region occurs in the neurological territory of the affected structure of the brain
almost always chronic
responds poorly to conventional anaesthetics
what are some methods to stop pain transduction?
NSAIDs
Ice
rest
what are some methods to stop pain transmission
opioids
anticonvulsants
DREZ
cordotomy
what are some ways to stop pain perception?
distraction
relaxation
mirror box therapy
cognitive behavioural therapy
does chronic pain serve a protective function?
no
what are some ways to stop descending modulation of pain?
opioids
antidepressants
spinal cord stimulation
