Pain and nociception Flashcards
Pain definition
an unpleasant sensory and emotional experience associated with actual or potential tissue damage
When is acute (nociceptive) pain evoked?
when intense/noxious stimuli threaten to damage tissues - induced sensory reception
What is the adaptive/biological function of acute pain?
protective function
What is the threshold of acute (nociceptive) pain?
high threshold (difficult to recruit nociceptor endings)
What is the duration of acute (nociceptive) pain?
limited duration
Which afferent fibres are associated with acute (nociceptive) pain?
Ad (A delta) and C fibres
Describe the structure of Ad fibres?
thinly myelinated with a small diameter axon (1-5um)
Describe the structure of C fibres
unmyelinated with a very small diameter (0.2-1.5 um)
What sensation is associated with first pain?
sharp, stabbing pain
Which axon does the sharp, stabbing first pain correspond to?
Ad fibres
What is the sensation of the second pain?
dull, aching pain
Which axon fibre is associated with the perception of dull, aching second pain?
C fibres
What type of peripheral endings transduce noxious stimuli?
free nerve endings (unspecialised)
What axons do free nerve endings give rise to?
Ad and C fibre afferents
What stimuli activate Ad fibre nociceptor endings?
noxious mechanical / heat stimulus
What stimuli activate C-fibre nociceptor endings?
polymodal stimuli (e.g. temp, mechanical, itch)
How are nociceptor endings able to respond to different noxious stimuli?
nociceptor endings carry several types of receptor proteins that each respond to different stimuli
Nociceptor endings display sensitisation. What is meant by this?
the more the nociceptor endings are used, the more readily they are recruited (become more sensitive/responsive)
What is the name of the sensory pathway that transmits pain stimuli from the trunk/limbs?
spinothalamic pathway (somatic nociception)
What perceptions are felt as a result of the spinothalamic pathway?
pain, temperature, crude touch
What type of axon fibres can be the primary sensory neuron in the spinothalamic pathway?
Ad or C fibres
Describe the route of the primary sensory neuron in the spinothalamic pathway
the free nerve endings transduce noxious stimuli and the AP travels along Ad / C fibres into the dorsal horn where it synapses with the secondary sensory neuron
What is the name of the defined region of white matter the second order neuron relays information up through the spinal cord?
antero-lateral funiculus
Describe the path of the secondary sensory neuron in the spinothalamic pathway
conducts the impulse from the dorsal horn and crosses the midline to the opposite side of the spinal cord. Transmits information along the antero-lateral funiculus to the brainstem and then to the thalamus where it synapses with neuron 3