7. Pain Flashcards
What is the name given to pain receptors?
Nociceptors
What kind of stimuli do nociceptors react to?
Mechanical
Chemical
Thermal
What sources do chemical stimuli come from?
Damaged cells
Platelets
Immune cells
What chemicals are released from damaged cells?
Bradykinins
ATP
Prostaglandins
H+
What chemical is released from platelets?
Serotonin
What chemicals are released from immune cells?
Cytokines
Chemokines
Which receptors detect cold?
TRP A1
TRP M8
What receptor detects heat?
TRPV1
What receptor detects protons?
ASIC
What receptor detects bradykinin?
B1
B2
Which receptors detects mechanical stimuli?
DRASIC
mDEG
What kind of fibres are type 1 pain fibres?
A-delta
Small, myelinated, fast conduction
What sort of pain is transmitted through A-delta fibres?
Sharp, localised and immediate
Where does information from A-delta fibres go?
Thalamus and cortex
What NT is used in A-delta fibres?
Glutamate
What kind of fibres are type 2 pain fibres?
C
Small, unmyelinated, slow conduction
What sort of pain is transmitted through C fibres?
Dull, aching pain
Where does information from C fibres go?
Limbic system
Hypothalamus
What NT is used in C fibres?
Substance P
Which sensory pathway does pain travel in?
Spinothalamic
What tract in the spinal cord do A-delta and C fibres ascend in?
Tract of Lissauer
Where do A-delta fibres synapse in the dorsal horn?
Layers I and V
Where do C fibres synapse in the dorsal horn?
Layer II (Substantia gelatinosa)
When do the pain fibres decussate?
Immediately after synapsing with the second order neuron
Which receptors does glutamate act on?
NMDA
AMPA
Which receptor does Substance P act on?
NK1
What are endogenous opioids?
Chemicals released to help modulate pain
What are the 3 types of opioid receptors?
μ (heat)
δ (Mechanical)
κ (Visceral)
What endogenous opioids are released in response to heat?
β-Endorphin
Leu-Enkephalin
What endogenous opioids are released in response to mechanical stimuli?
Leu-Enkephalin
Met-Enkephalin
What endogenous opioids are released in response to visceral stimuli?
Dynorphin
Name 2 endocannabinoids
Anandamide
2-arachiodonylglycerol (2-AG)
What are endocannabinoids derived from?
Arachidonic acid
Which receptors do endocannabinoids work on?
CB1 (CNS)
CB2 (immune cells)
How do endocannabinoids mediate their analgesic effect?
Reduce Ca++ in presynaptic neuron to reduce NT release
What is gate theory?
Non-pain signals can inhibit the transmission of pain signals
How does gate theory work?
Large diameter Aα and Aβ fibres carrying non-pain stimuli stimulate interneurons in the substantia gelatinosa
Inhibit the transmission of pain between the 1st and 2nd order neurons using GABA and endogenous opioids
What are the origins of pathways that modulate pain?
Peri-ventricular and peri-aqueductal grey matter in the midbrain Rostroventral medulla (raphe nuclei)
Which NTs help in the modulation of pain?
Serotonin
Noradrenaline
What is meant by paresthesia?
Pins and needles
What is meant by dysesthesia?
Burning sensation
What is meant by hyperalgesia?
Low pain threshold or exaggerated pain response
What is meant by allodynia?
Pain in response to a stimulus that doesn’t usually cause pain
What is meant by deafferention pain?
Peripheral nerve lesions
Eg. Phantom limb
What is meant by psychogenic pain?
Pain that occurs with or without an organic cause, may be disproportionate to the organic cause
