Pain Flashcards
What is pain?
An unpleasant sensory and emotional experience associated with actual or potential tissue damage
Why is pain important?
- Promotes avoidance of situations which may decrease biological fitness
- Promotes resting behaviour that either enhances recovery or modifies behaviour so that further injury or death becomes less likely
What type of receptors detect pain?
Nocioceptors
How is pain sensed throughout the skin?
Free nerve endings
How is pain felt from internal organs?
In the local area on the outside of the body
How is intense pressure, stretching, shrinking and pinching felt?
High threshold mechanoreceptors, due to depolorisation and calcium influx
Vanilloid receptors and temperature gated channels sense what types of pain?
Heats, acids and capsaicin
What do vanilloid receptors flux?
Sodium, leading to an action potential
Where are vanilloid receptors found?
In the free nerve endings
What is released following tissue damage?
ATP
What is the circuit that causes you to withdraw from a painful stimulus?
Spinal reflex reaction - neuron, spinal cord interneuron - efferent motor neuron
What is the name of the neurons that send messages about the initial pain to the brain (before you’ve realised the pain has occurred)?
Procioceptors
What are the features of procioceptors?
Large diameter and myelinated
Name the fibres that carry messages about the first pain, and localisation of the painful stimulus?
Delta fibres
What fibres provide the secondary pain that is the continuing dull ache?
C fibres
Name the 2 pathways to the brain
- Somatosensory cortex via the thalamus
- To the emotional cortex, the insula and cingulate
What is hyperalgesia?
Noxious stimuli produce exaggerated pain sensation
What is allodynia?
Non-noxious stimuli produce pain sensation, eg touching burnt skin
What is released in peripheral sensitisation?
- Chemicals released as a result of tissue damage such as hydrogen and ATP
- Neuropeptides which trigger in the neighbouring blood supply the release of plasma
Histamine and NGF are examples of what type of cells?
Mast cells
Proteases cleave extracellular peptides to create what?
Bradykinin
What do COX enzymes convert arachidonic acid to?
Protaglandins
How does the nocioceptor become modulated so that it responds at lower pain thresholds?
- Components of the inflammatory soup such as bradykinin, NGF and prostaglandin feedback to their own receptors on the nocioceptor neurons
- The VR1 receptor is then phosphorylated and the threshold for firing changes
- A sensory nerve specific sodium channel is phosphorylated so threshold voltage for firing is decreased, making the nocioceptor more excitable and hypersensitive to stimulation
Why does pain increase sensitivity?
- Reminds you that you have hurt yourself
- Promoting the area for recovery
How do neuroplastic changed at the synapses in the spinal cord occur?
- Nocioceptive afferents release glutamate and substance P
- Substance P activates the KN1 receptor which leads to phosphorylation of the NMDA and AMPA receptors
- This means they become more responsive to glutamate and neurons become more excitable
- Substance P diffused to to other synapses and so wind up pain can spread causing generalised sensitisation to painful stimuli
What is gate-control theory?
When you hob up and down or blow on the area and it appears to reduce pain
Stimulation of the non-nocioceptive mechanoreceptors in the vicinity of the injury activates neurons where? The activation of these neurons stops what neuron from firing?
- Dorsal horn
- Spinothalamic neuron
Competition between what two neurons switches off C fibres and prevents the pain signal from getting to the brain?
The nocioceptor and the inhibition from the propcioceptors
How much were burns patients pain ratings reduced by when in the VR condition?
30-50%
What is stress-induced analgesia?
Adaptive response to down-regulate pain
What is naloxine challenge?
An opioid antagonist which blocks the analgesic effect
Give an example of stress-induced analgesia
Soldiers escaping danger who don’t feel the pain of their wounds until in safety
Name three methods of reducing pain
Opiates, NSAIDS, cannabinoids, sodium channle blockers
What is neuropathic pain?
Pain caused by damage to the nerves themselves n