Pain and analgesics 1 Flashcards
What is pain?
The subjective conscious appreciation of a stimulus that is causing, or threatening to cause, tissue damage
What is nociception?
The physical process of detection and transmission of damaging or potentially damaging (noxious) stimuli
What are nociceptors?
Structures that detect noxious stimulus
What is algesia?
The induction of a condition leading to nociception and pain
What is analgesia?
Reduction or prevention of either nociception or pain without loss of consciousness
What is the detection of touch?
Mecanoception
Which specific structures are involved in the perception of touch?
Merkel’s Disc, Pacinian Corpuscle, Meissners Corpuscle
What are the two main types of nociceptor?
Polymodal, mechanical
What type of mechanical stimuli do both types of nociceptor respond to?
High intensity
What level of thermal input can stimulate polymodal nociceptors?
> 45 degrees, <10 degrees
What level of thermal stimuli can stimulate mechanical nociceptors?
> 60 degrees
What is the order of structures for detecting a noxious stimulus?
Skin/viscera–> Sensory receptor–> primary afferent axon–> spinal cord
What are the types of receptor in nociceptors?
ASIC (acid sensing ion channel), Purinergic receptors (P2x3), Voltage gated Na+ channels, VR-1/TRPV-1
What is the main agonist of ASICs?
Protons
What is the main agonist of Purinergic receptors?
ATP
What type of stimulation do purinergic receptors respond to?
High intensity mechanical stimulation
What type of stimulation do voltage gated sodium channels respond to?
Mechanical stimulation
What is the main agonist of VR-1/TRPV-1?
H+, high levels of heat and capsaicin
Speed of nociceptive APs compared to touch APs?
Slower
Why are nociceptive APs slower than touch ones?
The C fibres are very thin and unmyelinated
Which type of fibre is used for nociception?
C and a delta
Which type of nociceptor is linked to c fibres?
Polymodal
Which type of nociceptor is linked to A delta fibres?
Mechanical
Why do APs flow down Adelta fibres quicker than C fibres?
The Adelta fibres are myelinated
Why is there an initial pain felt, then a throbbing?
Different fibres transmit at different speeds so one transmits slower after the other
Which fibres are responsible for the initial pain?
A delta
Which pain fibres are responsible for the second pain?
C fibres
Which receptors detect reasonable temperatures (10-40 degrees)?
Thermoreceptors
Which receptors detect extreme temperatures?
Cold/heat pain receptors
Why do thicker fibres transmit APs quicker?
There is less resistance
Where does sensory input enter the spinal cord?
Through the dorsal root
Where is the first synapse (in the spinal cord) that is responsible for nociceptive input into the brain?
The most dorsal part of the spinal cord
Where does the AP go after it has gone through the first synapse in the spinal cord?
Crosses over to the other side of the body and goes up into the brain
What can the somatosensory part of the cortex receive input from?
Touch and nociception
What does the somatosensory cortex do with the touch and nociception?
Tells the brain where it has come from
Role of insular and anterior cingulate cortex in nociception?
Tells the brain that it is pain that is being experienced, affect your mood
How is the body mapped regarding pain perception and location?
As you go round the outside of the somatosensory cortex, different parts of it receive input form different body areas
What is the pain pathway to the brain?
Spinothalamic pathway/tract
Why is pain referred?
Not enough space in somatosensory cortex to have an acute sensation to map every part of the bodys pain
Which body parts have a good pain mapping (know where the pain is coming from)?
Skin
Which body parts have a poor pain mapping (don’t know where the pain is coming from)?
Internal organs
Where does pain sourced in the oesophagus feel like its coming from?
Heart
What can hurt when having a heart attack?
Left arm
Which neurons are shared in referred pain?
Second order
What is the second order neuron?
The one after the first synapse in the spinal cord
What is hyperalgesia?
Increased response to a noxious stimulus
What is allodynia?
Painful responses to a non-noxious stimulus
Why is hyperalgesia a thing?
To protect already injured/damaged areas of the body
How does nociceptor sensitisation work?
Cut skin–> skin cells break–> intracellular components of skin cells is released into extracellular space–> some of these components are H+, ATP, K+ which are nociceptor agonists
Why does an elevated conc of extracellular K+ increase the amount of APs fired from a neuron?
Conc grad is disrupted meaning it is harder for the neurons to repolarise, makes them more excitable
What is unusual about nociceptive neurons?
They can release NTs from their dendritic end
Which NT is released from the dendritic end of nociceptive neurons?
Substance P
What does substance P do to blood vessels?
Activate receptors on blood vessels that makes them leaky
Outcome of substance P’s action on blood vessels?
More nociceptor agonists are released, generating more nociceptive APs
Which cells does substance P recruit?
Mast cells
Action of mast cells?
Release histamine which makes blood vessels leaky
Which three molecules are used for healing the part of the body that has been damaged?
Bradykinin, prostagladin, neural growth factor
What does nerve growth factor do?
Sensitise the nociceptors by lowering their threshold for opening
What is peripheral sensitization?
Increased sensitivity of peripheral nociceptors
What is central sensitization?
Increased transmission in spinal cord
Which fibres do itch sensations travel down?
Adelta and C
Difference between pain and itch?
Analgesics don’t inhibit itch, can imagine an itchy sensation but not a painful one
What kind of input cures an itch?
Nociceptive (scratching it hard)
