1. © UWCM/SONMS/Pain/MJohn
Pathways
© UWCM/SONMS/Pain/MJohn

2. Receptors trigger pain perception and the pain response
Examples:
Mechanoreceptors
thermoreceptors.
photoreceptors &
chemoreceptors
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3. Structure of a Sensory Neurone
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4. Pain/Sensory receptors in the Hand
© UWCM/SONMS/Pain/MJohn

5. © UWCM/SONMS/Pain/MJohn

6. © UWCM/SONMS/Pain/MJohn
Saltatory Conduction
© UWCM/SONMS/Pain/MJohn

7. © UWCM/SONMS/Pain/MJohn

8. Perception of Painful Stimuli
Remember that Nociception is the response to noxious (painful) stimuli. It comes from nerve endings that respond to high intensity mechanical, thermal and chemical stimuli
© UWCM/SONMS/Pain/MJohn

9. Pain receptors are widespread
Skin,
Periosteum,
Joint surfaces,
Arterial walls,
Subcutaneous tissue
Muscle,
Fascia and viscera.
Most deep tissues have few pain receptors (Bonica, 1990).
© UWCM/SONMS/Pain/MJohn

10. © UWCM/SONMS/Pain/MJohn
SOURCE of PAIN
© UWCM/SONMS/Pain/MJohn

11. © UWCM/SONMS/Pain/MJohn
Cutaneous fibres.
myelinated, type A ‘delta' fibres or
unmyelinated, type C fibres
Myelinated A delta fibres conduct acute prickling type pain whereas
Unmyelinated C fibres transmit the slower burning dull, diffuse, persistent unbearable pain sensations
© UWCM/SONMS/Pain/MJohn

12. Myelinated and Unmyelinated Fibres
© UWCM/SONMS/Pain/MJohn

13. © UWCM/SONMS/Pain/MJohn
Clinical Links
Ischaemia
Pain from ischaemic toes is transferred via free nerve endings to the spinal cord and on to the brain even without other stimuli
Distension of organs like the gut
Free nerve endings that respond to such stimuli that can cause tissue damage.
© UWCM/SONMS/Pain/MJohn

14. Tissue damage & Pain-producing substances
Activating Receptors
H+ and K+ - released from damaged tissue
ATP released from damaged tissue
Bradykinin - released from plasma and very potent
Histamine - released from mast cells
Serotonin(5HT)- released from platelets around damaged tissue
© UWCM/SONMS/Pain/MJohn

15. Sensitising Receptors
Prostaglandin - released from damaged cells
Substance P -released from affected nerve terminals
Leukotrienes - released from Mast cell Eosinophils & Macrophages
© UWCM/SONMS/Pain/MJohn

16. © UWCM/SONMS/Pain/MJohn
Inflammation & Pain
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17. © UWCM/SONMS/Pain/MJohn
Dorsal Horn
Afferent Sensation reaches the Dorsal Horn
It reaches s set of Lamina with the substantia gelatinosa
© UWCM/SONMS/Pain/MJohn

18. Acute Pain Perception &Transmission
Histologically, the grey matter of the spinal cord is divided into ten 'laminae'.
The dorsal part is divided into five laminae (I to V), components of which deal with most incoming pain fibres.
© UWCM/SONMS/Pain/MJohn

19. Pain Pathway to the brain
© UWCM/SONMS/Pain/MJohn

20. © UWCM/SONMS/Pain/MJohn
Spinothalamic Tract
© UWCM/SONMS/Pain/MJohn

21. © UWCM/SONMS/Pain/MJohn
Gating mechanisms 1
Tiny unmyelinated 'C' fibres carriers of the long-lasting burning pain e.g. surgical wounds.
Thin myelinated 'A delta' fibres, more accurate localisation of pain, terminating in laminae I and V.
Chunky 'A beta' fibres carry information on vibration + position
© UWCM/SONMS/Pain/MJohn

22. © UWCM/SONMS/Pain/MJohn
Gating Mechanism 2
Stimuli entering via the C fibres can be suppressed by concurrent stimulation of A delta fibres (high amplitude low frequency stimulation, e.g. acupuncture) or
A beta fibres impulses. E.g. TENS (transcutaneous electrical nerve stimulation) and rubbing the skin,
© UWCM/SONMS/Pain/MJohn

23. © UWCM/SONMS/Pain/MJohn
Pain Modulation
Peripheral tissues -
At the gate
Central
CNS
PNS
© UWCM/SONMS/Pain/MJohn