746 Human Brain
Pain
Pain : Aim perception peripheral responses
role of NSAIDs e.g. aspirin spinal modulation
gate control peptidergic modulation
CNS
Perception pain
human description International Association for the Study
of Pain: "Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage".
phantom pain amputees
Why do we need pain?
Peripheral responses Specialised receptors Pain is not just neurons firing more
often Adequate stimuli Role of
aspirin Paracetamol Ibuprofen
Specialised receptors Heinbecker 1933 A-
faster than 2.5m/s high threshold mechanoreceptors - 20
cm-2
sharp pain C
slower than 1m/s polymodal
heat - pressure - noxious chemicals
Adequate stimuli temperature
C fibers sensitive to very low concentrations of histamine 10-8M, ACh 10-8M Prostaglandins 10-10 M no one chemical ??
released by tissue damage
Capsaicin transient effect of chillies - capsaicin Loss of nocioceptive response in new
born rats with capsaicin
Role of aspirin
aspirin blocks Cyclooxygenase = COX = PGH synthase
covalent modification to ser - 530 http://cti.itc.virginia.edu/~cmg/Demo/pdb/cycox/
cycox.html
arachidonic acid COX
prostaglandin PGG2COX
prostaglandin PGH2
Other NSAIDs non-steroidal anti-inflammatory drugs Ibuprofen
COX competitive inhibitor Paracetamol
= Acetaminophen = N-acetyl-para-aminophenol COX-3 inhibitor
Summary so far Pain perceived A - and C fibres response to pain blocked by NSAIDs
prostaglandin synthesis
Next: Spinal cord...
Neuromatrix Melzack & Wall revised their theory to
elaborate on the spinal cord system as neuromatrix
Enkaphalins in SG drawing of
nocioceptive cell in SG
enkephalin immunoreactive
enkephalin receptors
mu delta kappa
Substance P 11 amino acid peptide Arg Pro Lys Pro Gln Gln Phe Phe Gly
Leu Met Found in CNS and dorsal horn of spinal
cord Example of a tachykinin
Summary so far: spinal modulation gate control or neuromatrix tactile stimuli TENS SG SP opioids
next: CNS
CNS CNS itself not
sensitive to pain meninges are -
local anaesthetic regional
specialisation leucotomy
removal of frontal lobes / thalamus to remove pain perception
PET scan shows blood flow