Pathophysiology of Pain Flashcards
what is pain?
an unpleasant sensory and emotional experience which is associated with tissue damage
is pain a stimulus ?
no
- pain is a perception of a stimulus
where does pain perception occur in the brain ?
somatosensory cortex
from the dorsal root the neurone cross over to the contralateral side before moving up the spinal cord ?
- where then does the neuron go after this to get to the thalamus ?
brain stem
mid brain
thalamus
what three areas can the neurone go after the thalamus to get a response ?
somatosensory
limbic system
cingulate cortex
where does gate control modulation from descending PAG come from?
Limbic system
what are the four steps of pain perception ?
- detection in the periphery
- processing and transmission in the spinal cord
- perception and response in the brain
- modulation in the descending tracts
what is nociception ?
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 stimulus is detected by nociceptors?
response to - thermal - chemical - mechanical noxious stimulus
describe the path of the 1st order neurones ?
start at the skin and move into the dorsal horn cross over to the contralateral side and synapse at the thalamus
what are the 4 types of primary afferent fibres ?
A alpha
A beta
A delta
C fibres
which fibres are most myelinated ?
A alpha
A beta
which primary afferent fibre is unmeylinated ?
C fibres
what neurons are used for touch ?
A alpha
A beta
what fibre is used for fast pain?
A delta
what fibres are used for slow fibres ?
C fibres
is grey matter on the inside or outside ?
inside
what does PAG stand for?
Periaqeductal grey
where abouts is the Periaqeductal grey in the mid brain?
lateral to the cerebral aqueduct
does the PAG usually increase or decrease the nociceptor signal?
usually decreases as the stimulus is determined to not be noxious
what neurotransmitter is released from the PAG system ?
noradrenergic
what area is part of descending control of pain?
PAG
what is hyperalgesia ?
Increased perception of pain of non-noxious stimuli as noxious stimuli
- the threshold for pain perception is reduced so non-noxious stimulus are painful
- exaggerated response
what is allodynia ?
decreased threshold for a response
- hyperalgesia that to light touch
what is spontaneous pain ?
spontaneous activity in nerve fibres
when can spontaneous pain occur?
post surgery if a nerve has been cut and an axon triggering APs spontaneously causing pain
what three neurones synapse with the dorsal root projection neuron ?
interneurone
primary afferent neurone
descending neurone from PAG
what are the three main components of central sensitisation ?
wind up
classical
long-term potentiation
what does central sensitisation result in ?
chronic pain
what is peripheral sensitisation ?
when the threshold for pain is reduced so patents feel pain chronically
what are the three types of peripheral sensitisation ?
allodynia
hyperalgesia
spontaneous pain
what is the difference between peripheral and central sensitisation ?
peripheral results in 1st neurone sensitisation
central results in 2nd neurone sensitisation
when a stimulus is triggered during central sensitisation does the component “wind up” occur?
yes
when the stimulus is stopped does central sensitisation wind up still occur ?
no
- wind up only occurs when the stimulus is present and neurotransmitters are being released
state what occurs during wind up central sensitisation
when there is a stimulus there is an exaggerated response and many neurotransmitters are released
is the wind up component of central sensitisation homosynaptic or heterosynaptic ?
homosynaptic
how does the classical component of central sensitisation work?
involves opening up new synapses
is the classical component of central sensitisation homosynaptic or heterosynaptic ?
heterosynaptic
- because other new neurons are introduced
when the stimulus is stopped, does the central sensitisation component classical continue ?
yes
- the classical component will outlast the initial stimulus as “silent nociceptors” have been activated
what is secondary hyperalgesia ?
where the area surrounding the injury site is also painful and where the touch also becomes painful
when does the classical component of central sensitisation occur?
when the intensity of stimulus is high the neurones call in help from silent nociceptors
when does long -term potentiation occur?
with very intense stimuli
does long term potentiation involve activated or inactive synapses ?
activated
what is nociceptive pain?
A sensory experience that occurs when specific peripheral sensory neurones (nociceptors) respond to noxious stimuli
What is neuropathic pain?
Pain initiated or caused by a primary lesion or dysfunction in the somato-sensory nervous system
does acute pain serve protective function?
yes
does chronic pain serve protective function?
no
can acute pain occur without noxious stimuli ?
no
can chronic pain occur without noxious stimuli ?
yes
is nociceptive pain typically localised ?
yes
how is nociceptive pain usually described ?
throbbing
aching
stiffness
is neuropathic pain localised ?
may not be localised to the site of injury
does neuropathic pain respond well to analgesias ?
no
does nociceptive pain respond well to analgesias ?
yes
what are the four stages that pain can be modulated by medical intervention ?
transduction
transmission
perception
descending modulation
what four options is there for transduction pain ?
NSAIDs
Ice and warm packs
Rest
Local anaesthetic blocks
what pain modulation options are there for transmission stage ?
nerve blocks
opioids
anticonvulsants
surgery
how can perception be changed to modulate pain ?
education cognitive behavioural distraction relaxation graded motor imagery mirror box therapy
what options are available for descending modulation of pain?
placebos
opioids
antidepressants
spinal cord stimulation
is pain subjective ?
yes
does chronic pain serve any protective function ?
no
