Please enable JavaScript.
Coggle requires JavaScript to display documents.
NS13 - Mechanism of Pain Perception (i) (Nociceptors (noxious stimuli…
NS13 - Mechanism of Pain Perception (i)
pain
unpleasant sensory + emotional experience
not always caused by tissue damage (e.g. neuropathic pain)
pain perception has info + emotional components (subjective experience, e.g. how much attention is payed)
acute
real/potential tissue damage
appropriate protective mechanism
transcient , reversible
can be long-lasting
can become pathological (Chronic)
persistant
irreversible
Nociceptors
pain Rs
free N endings
can be mechanoRs, thermoRs, chemoRs
cold: CRM1
heat: VR1
protons: ASIC
bradykinin: B1/2
mechanical: DRASIC/mDEG
noxious stimuli cause pain (potential to cause tissue damage
bradykinin, PGs, H+, ATP (when released from damaged cells, acts @ proline Rs), serotonin (when released from platelets), cks, chemokine
A delta fibres
pain fibres that produce sharp, highly localised, specific + immediate pain
relay info via thal to SS cortex
tiggers immediate withdrawal + allows localisation
small fast myelinated
conduction speed = 12-30m/s
C fibres
pain fibres that produce dull diffuse pain
relay info to limbic system (emotional response) + hypothal
small slow unmyelinated
conduction speed = 0.5 - 2 m/s
pain pathway = sensory
3 neurons...
primary afferent from nociceptor to cord
spinothalamic tract to thal
thal to SS cortex
pain from face: cranial Ns
Nociciceptive fibres in dorsal horn of cord
upon entering cord, A delta + C fibres asend in tract if Lissauer (right side)
then they synapse with 2nd order neurons
usually in substantial gelatinosa
superficial layers of doral horn, laminae 1+2
but A delta fibres terminate deeper (lamina 5)
collection of cells found @ all levels
decussation after 1/2 cord segments
Glutamate
main NT for pain
via NMDA + AMPA Rs
needs co-NT: substance P via NK1 R
response to noxious stimuli
conscious pain perception
spinal withdrawal reflex
ANS changes
emotional response
visceral pain
referred to somatic structures sharing spinal segment with visceral afferent (felt in areas removed from site of stimulus - i.e. corresponding dermatome)
poorly localised due to convergence of visceral + somatic afferents on dorsal horn neurons
brain incorrectly interprets as coming from somatic structures
Pain perception can be modulated
gate theory of modulation in dorsal horn
descending pathways influence dorsal horn modulation
endogenous analgesics
GABA
cannabinoids
opiates
leu/met enkephalins
beta-endorphin
dynorphin
located @ sites associated with pain modulation
act @ opioid Rs
mu for heat
dela for mechanical pain
kappa for euphoria