Flashcards in Lecture 26 - Neurochemistry: Pleasure and Pain 1 Deck (19):
Pain is always...
The relationship between tissue damage and pain is _____
variable, so the size of an injury can be a poor guide as to how much pain some is in
Pain is expressed in _______
behaviour - that is how we communicate to others
What is the differences in somatosensroy and pain nerves?
Pain - nociceptors project straight to dorsal horn, then straight to the thalamus, and then to the cortex
touch and sense pathways has an extra secondary neuron between the dorsal coloumn nuclei and the thalamus
low- threshold C-fibre mechanoceptors have been linked to...
High- threshold C-fibre mechanoceptors have been linked to...
noxious pain /itch
What is TRPV1?
a transducer in polymodal nociceptors - activated by capsaicin
activation leads to ca2+ going into the cell and firing the nerve
Also responds to heat
c-fibres are polynodal meaning...
they respond to different stimuli - mechanical and chemical
A-delta fibres are what class of nociceptor?
Thermal and Mechanical
Local anaethetic drugs work to block pain because...
they just non-selectively block the voltage gated sodium channels, meaning all axons cannot propagate APs
Which conducts faster out of the niciceptors?
a-delta fibres are myelinated - faster
c-fibres are not (stub your toe, delayed pain 1,2 seconds)
Response to noxious heat on back and front of hand.
Which fibres do what?
back (hairy) - Ad fibres deliver sharp pain, follwed by c-fbres with slow, burning pain
On palm of hand, there are only c-fibres (slow burning pain only)
How is the segreation of nociception organised in the SC?
In the spinothalamic tract there is functional and anatomical separation
most pain related info is carried into the superficial layer (right at the top)
lamina 1,2 - info from c and a fibres
Consider the defensive spinal reflexes where are these neurons contained?
all within the SC - independent of the perception of pain, brain not involved (but can modulate)
there is an amplificaiton of pain from the same level of stimulus
reduction of pain threshold
What causes Primary hyperalgesia?a
damaged skin releases inflamatory mediators and chemicals
These act on the nociceptor terminals and make them more sensitive
What is secondary hyperalgesia or allodynia?
When mechanical neurons contribute to pain via a sensitised central pathway (within the SC)
The somato sensorycortex is organised to specific ...
parts of the body - can still be active in amputated limb which gives rise to pain in phantom limbs