Pathophysiology of Pain Flashcards
what is pain?
an unpleasant sensory and emotional experience which we primarily associate with tissue damage or describe in terms of damage.
is pain a stimulus?
no
describe the pain pathway from the periphery to modulation
> periphery there is detection and transmission to the spinal cord via first order neurons
spinal cord there is processing and transmission to the brain (thalamus) via second order neurons
brain there is perception, learning and response
modulation is the descending tracts
what is nociception?
the detection of tissue damage by specialised 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 is the first order neurons cell body?
in the dorsal root ganglion
describe A alpha and A beta fibres
> myelinated
large diameter
proprioception and light touch
describe A-delta fibres
> lightly myelinated
medium diameter
nociception
fast/sharp pain
describe C fibres
> unmyelinated
small diameter
slow conducting
innocuous temperature, itch, dull pain
describe the neurons that will receive the input in the spinal dorsal horn
> nociceptive specific
low threshold mechanoceptive
wide dynamic range
what does the lateral spinothalamic tract convey?
fast and slow pain (pain and temperature sensations)
what does the anterior spinothalamic tract convey?
sensation of simple touch
what rexed lamina does the spinothalamic tract arise from?
2 and 5
what is the second relay station?
the thalamus
what are the connections to the thalamus?
> cortex
limbic system
brainstem
where does pain perception occur?
in the somatosensory cortex
what is hyperalgesia?
increased perception of pain or even the perception of non-noxious stimuli as noxious.
when does hyperalgesia occur?
whenever there is a tissue injury and inflammation, it occurs in the surrounding uninjured tissue
what is allodynia?
is type of hyperalgesia where there is a decreased threshold for pain
describe the changes in nociceptor in allodynia
there is decreased threshold for response
describe the changes in nociceptor in hyperalgesia
exaggerated response to normal and supranormal stimuli
describe gate control theory
non painful input closes the gate to the painful input, stopping it from travelling to the central nervous system. stimulation of a non-noxious input is able supress pain
describe the changes in nociceptors in spontaneous pain
there is spontaneous activity in nerve fibres
what is central sensitisation?
the response of second order neurons in the CNS to normal input both noxious and non-noxious
name three main components in central sensitisation
> wind up
classical
long term potentiation
describe wind up central sensitisation
> involves only activated synapses
homosynaptic activity dependent progressive increase in response of the neurons
manifests over the course of the stimuli and terminated with the stimuli
in classical central sensitisation what is opened up in the dorsal horn?
new synapses, silent nociceptors
in classical central sensitisation what is heterosynaptic activity dependent on?
plasticity
describe onset of classical central sensitisation
it is immediate with the appropriate stimuli
can the classical sensitisation outlast the initial stimuli duration?
yes and it can be maintained at low levels of ongoing stimuli
describe long term potentiation
> involves mainly activated synapses
> occurs primarily for very intense stimuli
what conditions involves supracentral sensitisation?
> fibromyalgia
chronic widespread pain
painful physical symptoms of depression/anxiety
describe acute pain
> less than a month > usually obvious tissue damage > increased nervous system activity > resolves on healing > serves protective function > usually nociceptive
describe chronic pain
> 3-6months or more > beyond expected period of healing > no protective function > degrades health and function > nociceptive/neuropathic/mixed
what is nociceptive pain?
a sensory experience that occurs when specific peripheral sensory neurons respond to noxious stimuli
in nociceptive pain is there often specific localisation?
yes, often describes and throbbing, aching, stiffness
what is neuropathic pain?
pain initiated or caused by a primary lesion or dysfunction in the somatosensory nervous system
describe the painful region in neuropathic pain
it is not necessarily in the same region as the site of injury but occurs in the neurological territory of the affected structure
which responds to conventional analgesics better, nociceptive pain or neuropathic pain?
nociceptive pain
what works on transduction of pain?
> NSAIDs
Ice
Rest
LA blockers
what works on transmission of pain?
> nerve blocks
drugs (opioids, anticonvulsants)
surgery (DREZ, cordotomy)
what works on the perception of pain?
> education > congnitive behavioural therapy > distraction > relaxation > graded motor imagery > mirror box therapy
what works on descending modulation?
> placebos
drugs (opioids, antidepressants)
surgery (spinal cord stimulation)
