Pain Flashcards
What is pain
An unpleasant sensory or emotional experience associated with actual or perceived tissue damage- a product of higher brain processing
What is congenital insensitivity to pain
Don’t feel pain, can easily injure yourself
What can cause congenital insensitivity to pain
Na+ channel mutation, nerve growth factor mutations, overexpression of opiods
Congenital insensitivity to pain- Na+ channel mutation
Mutations in the voltage-gated Na+ channel in pain afferent neurons, means info about noxious stimuli is not transmitted
Congenital insensitivity to pain- nerve growth factor mutations
Mutations in NRTK1, the nerve growth factor necessary for the growth and survival of nociceptive neurons
Congenital insensitivity to pain- opiods
Overexpression of opioids, the brain’s natural pain relief
How does congenital insensitivity to pain suggest pain and touch pathway are separate
Sensation of touch is normal in these disorders
What are the 3 main types of nociceptors
Adelta mechanosensitive, Adelta mechanothermal, and C fibre polymodal receptors
What sort of structure do Adelta and C fibres have
Free nerve endings, thin, Adelta is slightly wider and myelinated
What types of temp do Adelta and C fibres detect
Adelta- cold thermoreceptors
C fibres- warmth receptors
What sort of touch and pressure do Adelta’s free nerve endings detect
Crude touch- we’d only be aware of it if our dorsal columns were damaged
What are nociceptors
Sensory receptors that respond to dangerously intense stimuli to signal that tissue is at risk of being damaged
What is the threshold of nociceptors
High thresholds of stimulation
What is the receptive field size of nociceptors
Large receptive fields
A delta < C fibres
What neurotranmitters do Adelta and C fibres release at the first synapse
Adelta- glutamate
G fibres- glutamate and substance P
What is the consequence of the large receptive field sizr of nociceptors
Make fine localisation difficult, but this isn’t really necessary, more important you feel the pain
What stimulation do Adelta mechanothermal nociceptors respond to
Dangerously intense thermal stimulation
What stimulation do Adelta mechanosensitive nociceptors respond to
Dangerously intense mechanical stimulation
What do C fibre polymodal receptors respond to
Have lots of receptors that bind to different ligands produced in tissue injury, and report back using EPSPs from all the different ligands present
Where do the nociceptors first synapse
Substantia gelatinosa in spinal cord
What is substance P
Neuropeptide, no obvious clearance mechanism so hangs around a lot longer, can cause prolonged depolarisation when they bind to the NK1 receptor AKA hyperalgesia
What is the result of the different fibres having different conductino speeds
First pain- sharp, brief better-localised pain (Adelta)
Second pain- duller, poorly -localised long-lasting pain with a burning quality (C fibre)
How can we isolate the effect of Adelta vs C fibres
Can selectively block either pharmacologically, can separately stimulate each fibre to elicit 1st vs 2nd pain
Experimental demonstration that nociception involves specialised neurons NOT greater discharge of neurons that respond to normal stimulus intensity
Applying increasing heat to a hand gradually increases firing rate of thermoreceptors, but thermosensitive nociceptors only become active when the heat becomes noxious (45degC), at which point the normal thermoreceptors are at max rate