Unit 7 - Pain Flashcards
pain definition
an unpleasant sensory and emotional experience associated with potential or actual tissue damage, or described in terms of such damage
nociception
process of transmitting painful stimulus
categories of acute pain
somatic
visceral
somatic acute pain
superficial e.g. skin, deep e.g. connective tissue, bone etc
well localised, protective role, promote healing
visceral acute pain
internal organs - distension of organs e.g. colic or inflammation e.g. appendicitis
poorly localised - less nociceptors ⇒ larger receptive fields ⇒ pain not well localised
chronic pain
long term debilitating pain
altered pain perception
e.g. rheumatoid arthritis, phantom limb pain
Not protective, does not promote healing
Aδ nociceptors
proportion of receptors
responds to…
diameter
type of pain
20%
respond to mechanical stimuli - tissue injury
small diameter myelinated fibres
sharp, prickling, bright, well localised pain - ouch and withdraw
C nociceptors
proportion of receptors
responds to…
diameter
type of pain
80%
respond to mechanical, thermal, chemical stimuli - polymodal
small diameter unmyelinated fibres
slow, burning, aching, diffuse pain
Finger on hot surface - withdraw first - Aδ fibres activated - then slow pain by C fibre
C fibres - type of nerve ending
ion channels located on these nerve endings
free nerve endings
mechanical
cold
heat
chemical noxious stimuli
inflammatory mediators
act to reduce pain threshold of nerves
COX inhibitors as analgesics
where do Aδ fibres terminate
lamina I and V
where do C fibres terminate
lamina I and II
lamina II
synonym
NTs associated
type of AP
substantia gelatinosa
modulation of pain
number of NTs released (excitatory) e.g. glutamate and substance P
EPSP - AP
Lots of interneurons that can change and modify the pain stimuli
flexation reflex =
fibres activated
withdrawal from painful stimulus
Aδ activation leads to activation of excitatory and inhibitory interneurons in spinal cord
contraction of agonist muscle and withdrawal from stimulus
anterolateral system =
spinothalamic tract
In order to recognise where the stimulus is coming from - fibres come from spinothalamic pathway
parallel pain pathways - sensory
sensory discriminative aspects of pain
location, intensity, quality
2nd order neurons synapse in thalamus
3rd order neurons to SI and SII
parallel pain pathways - motivational-affective dimensions of pain
cognitive, emotional and motor aspect of pain
2nd order neuron terminate in thalamus and brainstem - spinoreticular pathway
3rd order neurons terminate in SI and SII and onto other brain regions
3rd order neurons terminate prefrontal cortex, amygdala, hippocampus, descending pain pathway
pain experience and modulation
spinal modulation of pain - interneurons
spinal cord contains many inhibitory transmitters that may be anti-nociceptive (interneurons) - a mix of excitatory and inhibitory
endogenous opioids
endogenous cannabinoids
NA, serotonin
GABA
tonic activity in all of these neurons
modulation by descending pain pathway
role for glial
incoming non-nociceptive transmission
pain gate theory =
local projections also modulate pain transmission
what functions as a gate
what opens and closes this gate
substantia gelatinoas (lamina II of spinal cord)
small unmyelinated C fibres open gate - facilitate lateral spinothalamic tract activation
large myelinated fibres (Aβ - mechanoreceptors - on the skin - ruffini etc) close gate - inhibit laternal spinothalamic tract activation
why does rubbing or scratching help reduce pain signal
balance of excitatory and inhibitory processes
mediated via interneurons
rubbing, scratching, TENS (Trans Electrical Neural Stimulation)
pain gate theory
Activation of spinothalamic pathway and we inhibit any inhibitory neurons that dampen down signalling at the 2nd order neuron
how does stress modulate pain
acute stress decreases pain - descending inhibition
chronic stress increases pain - descending facilitation
descending pain pathway
Comes from all areas of brain
Signals to periaqueductal grey - sends projections to brainstem to SC
Either inhibit or activate interneurons and influence no of APs generated in ascending pathway
brain modulation of nociceptive transmission
referred pain
Somatic and visceral pain receptors
Visceral are not as prevalent but will innervate the SC at the same level
Activate ascending projections
We feel pain
