Pain Flashcards
(23 cards)
pain is defined as
an unpleasant sensory or emotional experience associated with actual or potential tissue damage
(discriminative + emotional)
mechanical nociceptors (a delta)
activated by strong shearing force in the skin - cut/ strong blow/
-sharp pain
polymodal nociceptors (c fibres)
- both excitatory - Glu
respond to sharp blows, damaging heat > 46 deg
chemicals such as histamine, PG, bradykinin
- dull burning pain
a delta fibres
fast transmission = sharp pain/ myelinated
1-3
C fibres
slower transmission= dull, burning pain
- afferent CV explains 2 different types of pain
- 1,5,10 - viscera / diffuse pain
The gate theory
pain signals must overcome inhibition to reach the brain
- ensure only feel pain when appropriate
- inhibitory interneurons /projections, modulate response
- stimulated by excitatory afferents (ad/c)
the substantia gelatinosa
- laminar 2
- houses inhibitory interneurones
- direct/ indirect contact from afferents
During a non- noxious stimuli
- a-beta fibres- mechanoR activated
- excitatory synapse on the ascending projection
- excitatory synapse on an inhibitory IN
- causes an IPSP at the projecting N
- does not reach vT- no Pain experienced
during a noxious stimuli
- inhibition is switched off and ascending fibres fire APs
- excitatory afferents from c fibres
- synapse with another population of inhibitory IN within the SG
- these synapse with the gatekeeper N
- causes an IPSP at the GKN
- alleviates inhibitory signal from GKN and allows excitatory C fibre to excite ascending projection towards the brain (separate synapse)
- feel pain
closing the gate to prevent pain signal
- rubbing the injured area -n activation of a `beta fibres
- TENS - childbirth - activation of a beta fibres (excite GKNs)
- acupuncture
cortical level of the pathway
localisation of pain
subcortical level
perceive the stimulus as pain
limbic system
effective component
- emotional and affection aspects
The descending pathway (modulation of pain via brain)
- brainstem nuclei rich in opioids
- release of 5-HT, Nad, enkephalin (endogenous O)
- close the spinal gate
- intrinsic analgesia system
- swearing is an example
- very powerful
- inhibits ascending signals
normal physiological pain
- amount of pain experienced directly equal to the afferent input duration and intensity
persistent/ chronic pain
- increased sensitivity to pain
- promotes guarding and protection of an injured limb
- feel more pain to prevent aggregation of injury and further damage
- Process of peripheral and central sensitisation , modification of neurotransmission plasticity - feel more pain after a previous injury
- requires far less pressure to stimulate sensation of pain after a previous injury
- stimulus that was previously innocuous is now noxious
allodynia
level of stimulus wasn’t generating pain (innocuous) now generates pain
hyperalgesia
stimulus generates even more pain due to injury (was noxious)
neurogenic Inflammation
axon reflex - antidromic AP conduction
- peripheral release of substance P, CGRP from nerve ending
- induces swelling, plasma extravasation, immune cell migration and activation
- inflam soup
- Nerve ending expresses R of which these mediators bind to (cks etc)
- sensitisation of polymodal NC
- low stimulus intensity generates AP (lowered vT)
- idea of HA/ AD
secondary hyperalgesia
- promotes protection of secondary injury sites (indirectly injured sites)
- increased pain sensitivity distal from site of injury
- mechanisms in dorsal horn
primary hyperalgesia
- increased pain sensitivity that occurs directly in damaged tissue
low stimulus
- release of GLu from afferent
- binds to AMPAr present on SON
- single AP fired
- intensity and duration related to afferent input
facilitated pain
- neurogenic inflammation leads to more frequent firing of afferents
- SP released (only at high freq)
- preferential release
- increased AMPA stimulation activates NK-1
- change in conformation of NMDA r blocked by mg
- membrane sufficiently depolarised to relieve block
- NMDA involved in EPSP
- ca influx
- post SNN more responsive to input
- amplification of signal frequency sent to brain
