Lecture 10 Slides - Nociception and Pain(1)

Page 1: Introduction to Biological Psychology and Nociception

• Course Code: 4PSYC003W

• Subject: Biological Psychology

• Focus on the physiology of pain and nociception.

Page 2: The Physiology of Pain (Nociceptive Fibres)

• Afferent Fibre Groups:

  • Muscle Nerve:

    • Fibre Type: I (Aα)

      • Diameter: 13 – 20 μm

      • Conduction Velocity: 80 – 120 ms

  • Cutaneous Nerve:

    • Fibre Type: II (Aβ)

      • Diameter: 6 – 12 μm

      • Conduction Velocity: 35 – 75 ms

• Nociceptive Afferents:

  • Type III (Aδ): Smallest fibres

    • Diameter: 1 – 5 μm

    • Conduction Velocity: 5 – 30 ms

  • Type IV (C): Non-myelinated fibres

    • Diameter: 0.2 – 1.5 μm

    • Conduction Velocity: 0.5 – 2.0 ms

Page 3: The Pharmacology of Pain

• Key Components of Inflammatory Response:

  • Substance P: Triggers histamine release from mast cells.

  • Histamine, Bradykinin, Serotonin: Key mediators in pain and inflammation.

  • Potassium: Released during cellular lesioning.

  • Prostaglandins: Induce vasodilation and oedema.

Page 4: Pharmacology of Pain (Detailed Overview)

• Substances and Their Effects:

  • Potassium: Released by damaged cells, causes activation.

  • Serotonin: Derived from platelets, synthesized from tryptophan hydroxylase, induces activation.

  • Bradykinin: Comes from plasma kininogen via kallikrein, activation effect.

  • Histamine: Released from mast cells, effects activation.

  • Prostaglandins: Synthesized from arachidonic acid in damaged cells through cyclo-oxygenase, leads to sensitization.

  • Substance P: Found in primary afferent fibres, contributes to sensitization.

Page 5: Dorsal Horn Anatomy

• Spinal Cord Organization:

  • Focuses on the role of the dorsal horns in nociception.

Page 6: Spinal Level Functionality

• Dorsal Horn Fiber Types:

  • Aa/Aß Fibres: Responsible for touch and proprioception.

  • A Fibres II: Relate to sharper pain signals.

  • C Fibres: Associated with slower, dull pain signals.

  • Important Note: Thin dorsal root (C) fibres do not synapse directly onto spinothalamic cells; they use spinal interneurons for indirect influence.

Page 7: Spinothalamic Tract (STT) Overview

• Connections to the Thalamus:

  • Lateral STT: Responsible for fast and slow pain & temperature sensations.

  • Anterior STT: Processes simple touch sensations.

  • Fiber Types Included: Aδ and C fibres.

  • Role of Interneurons: Critical for signal integration.

Page 8: Fast Pain Pathway (Discriminative Aspect)

• Key Structures:

  • Medial Lemniscus, Thalamus, Somatosensory Cortex: Primary areas of fast pain processing.

• Main Targets for Fast Pain:

  • Ventral Posteriolateral nucleus (VPL)

  • Ventral Posteriomedial nucleus (VPM)

  • Posterior nuclei (PO)

Page 9: Slow Pain Pathways (Affective-Motivational Aspect)

• Pathways:

  • Medulla, Mesencephalon, Periaqueductal Grey Area (PAG)

  • Main Slow Pain Tracts: Paleospinothalamic tract, Spinomesencephalic tract, Spinoreticular tract.

• Slow Pain Targets:

  • Spinoreticular tract and Reticular formation

  • Spinomesencephalic tract targeting the PAG

  • Paleospinothalamic tract associated areas.

Page 10: STT Pain Targets in Thalamic Nuclei

• Thalamic Projections:

  • Fast pain projections mainly terminate in lateral (ventroposterior) thalamic nuclei.

  • Slow pain projections mainly in medial thalamic nuclei.

• Fast Pain Targets:

  • VPL, VPM, PO

• Slow Pain Targets:

  • NSIN and other medial/midline nuclei.

Page 11: Lateral Spinothalamic Tract Comparison

• Central Pathways for Pain Transmission:

  • Direct (Fast Pain) Tracts:

    • Lateral STT – subcortical targets: VPL, parietal lobe.

  • Indirect (Slow Pain) Tracts:

    • Involving cortical and subcortical targets like the limbic system.

• Functional Distinctions:

  • Discriminative pain vs. affective-arousal components of pain.

Page 12: From Periphery to Brain (Summary)

• Pathway Overview:

  • Nociceptive signals travel from the peripheral nociceptors through the primary afferent Aδ and C fibres to the dorsal root ganglion then the spinal cord, before reaching the thalamus and somatosensory cortex.

Page 13: The Pain Matrix

• Pain Systems in the Brain:

  • Medial Pain System: Processes pain localization, intensity, and emotional response.

  • Lateral Pain System: Focuses on sensory-discriminative functions and attention supervision.

  • Important Brain Structures Involved: Thalamus, insula, and frontal cortex along with the PAG.

Page 14: Relevant Examples in Pain Research

• Case Studies:

  • Ploner et al. on pain affect without sensation.

  • Ramachandran et al. on synaesthesia in phantom limbs.

Page 15: Central Control Mechanisms (PAG)

• Key Structures:

  • Periaqueductal Grey Area, Raphe Magnus nucleus also plays a role in pain modulation through descending pathways.

Page 16: 5-HT (Serotonin) Role in Pain Modulation

• Pathway Overview:

  • Serotonin pathways from the Raphe Magnus to the dorsal horn impact nociceptive signalling.

Page 17: Inhibition of Substance P

• Mechanism:

  • Inhibitory interneurons release Enkephalin to modulate pain through the inhibition of Substance P effects on dorsal horn neurones.

Page 18: References

• Key Literature:

  • Barbaro et al., Kandel et al., McLean et al., Ploner et al., Ramachandran et al., Reynolds on pain relief studies and related neuroscience research.