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Lecture 1 - Coggle Diagram
Lecture 1
Pain neural pathway
1) Nociceptors at end of afferent fibres sense pain stimuli.
2) Action potential ascends first order neurone of c fibres and A-delta fibres.
3) First order neurone ascends on left side of spinal cord
4) First order neurone synapses with second order neurone in spinal cord
5) Second order neuron decussates into right side of spinal cord
6) Second order neurone ascends anterior and lateral spinothalamic tract.
7) Second order neurone synpases with 3rd order neurone in thalamus.
8) Third order neurone ascends into somatosensory cortex
9) Somatosensory cortex process magnitude and location of pain.
Fundamentals bits
What are the 3 modalities of pain nociceptors?
Mechanical / tissue distension
swelling
pressure
Chemical
Endogenous
Histamine
Exogenous
Thermal
Polymodal
Sense >1 modality
Types of afferent fibres for pain
C-fibres
Small diameter of 0.2-1.5 μm
Unmeylinated
slow conduction velocity
suited for sensing dull pain
All capsaicin sensitive
Often polymodal
A-delta
Large diameter 1-5 μm
Myelinated
conduction velocity
suited for sensing sharp pain
Often mechano-heat nociceptors.
Not all capaicin sensitive
A-beta
Mechanoreceptor
Stimulates substania gelatinosa
Nociceptor example
TRPV1 / VR1
Polymodal
Heat
Inflammation
Chemical
Endocannabinoids
Capsaicin from chilli peppers.
Protons in acidosis
Bradykinin/ NK-1
5-HT
Ligand gated ion channel
Undergoes desensitization
Permeability
Calcium
Magnesium
Potassium
Sodium
Dorsal horn anatomy
Dorsal horn is split into superficial laminae layers.
Transmission neurone encompass superficial laminae 1 and 5
substania gelatinosa encompass superficial laminae 2.
Experimental techniques
Humans
Visual analog scale
Verbal pain intensity scale
Categorical scale
Animals
Tail Withdrawal Latency
Hot plate
visceral distention
sciatic nerve ligation
Modulation of pain
Dorsal horn Gate Control Theory
Increase pain signal
C fibre and A-detal fibre terminates at superficial laminae 1 and 5 in transmission nurone
transmission neurone relay action potential to second order neurone in thalamus
C fibre and A-delta fibres extend into substania gelatinosa to inhibit it from inhibintg transmission neurone.
Decrease pain signal
Laminae 2 in substania gelatinosa inhibits transmission neurone from relaying action potential to thalamus.
A-beta fibres connected to mechanoreceptors. Stimulates substantia gelatinosa.
Descending inhibitory control stimulates substania gelatinosa but inhibits transmission neurone.
Descending inhibitory control
Periaqueductal grey in midbrain stimulates nucleus raphe magnus, NRM which is a ventral region in medulla.
NRM sends inhibitory fibres into substania gelatinosa and transmission neurone in dorsal horn.
Inhibitory fibres extend from NRM to substania gelatinosa and transmission neurone.
Using 5-HT and enkephalin as neurotransitters to stimulate SG and inhibit tranmission neurone output to second order neurones.
Locus coeruleus also extends inhibitory fibres to dorsal horn using noradrenaline as neurotransmitter.