Nociception II lecture

Introduction

• Welcome to Noiception Two session with Q&A throughout

• Recap of key points from previous session

Nociceptors

• Nociceptors are specialized neurons

  • Cell bodies are located in the dorsal root ganglia

  • Have two axons for action potential generation

• Pain vs Nociception

  • Pain is a complex experience involving emotion and brain areas

  • Nociception refers to the detection of harmful stimuli

Action Potential Generation

• Nociceptors are stimulated through ion channels

  • Channel activation leads to depolarization and action potentials

  • First synapse occurs in the dorsal horn of the spinal cord

• Second-order neurons ascend via anterior lateral system (spinal thalamic tract)

Ion Channels in Nociceptors

• Variety of ion channels exist depending on nociceptive type (heat, pain, etc.)

• Importance of TRPV1 receptors for detecting capsaicin

• Mechanosensitive channels respond to mechanical pressure (like pinching)

Research on Nociceptive Mechanisms

• Experiments on rats anesthetized with urethane showed continued nociceptor activity

  • Brain interference does not stop peripheral response

• TRPV1 channel discovery example: separation and library creation from cells

• Study demonstrated genetic links to pain sensitivity

Plasticity of Pain

• Capsaicin can desensitize nociceptors upon repeated stimulation

• Culturing dorsal root ganglia and stimulation methods can yield insights into nociception

• Capsaicin cream can be used therapeutically for certain neuropathies

Integration of Nociceptive Signals

• Nociceptors converge in the dorsal horn of the spinal cord

• Neurotransmitter release (often glutamate) occurs here

• First-order neurons connect to second-order neurons ascending to the brain

Types of Nerve Fibers

• A-delta fibers: Thinly myelinated, 10% of sensory nociceptors, localized pain, 10 m/s conduction velocity

• C fibers: Unmyelinated, 90% of sensory fibers, slower conduction (1 m/s), diffuse and long-lasting pain

• Sensitized C fibers might cause allodynia, or pain without stimulation

Pain Mechanisms and Pharmacology

• Pain serves as a protective mechanism but can be debilitating

• Painkillers function through various mechanisms

  • Local anesthetics inhibit sodium channels, blocking pain transmission

  • Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit prostaglandin synthesis (Cox enzymes)

  • Opioid analgesics act on the central nervous system to modulate pain

• Long-term analgesic effects of certain drugs can vary

Modulation of Pain Signals

• Segmental control: Mechanoreceptors inhibit nociceptors in shared pathways

• Gate control theory: Touch activity can provide relief from pain signals

• The brain’s descending modulation can override incoming pain signals through opioid release

  • Enkephalins play a key role in stress and pain modulation

Conclusion and Recap

• Nociceptive research aids understanding of pain mechanisms

• Fast and slow pathways for pain processing and integration

• Research continues into how emotional and motivational aspects affect pain experience

• Recommended resource: "The Brain From Top to Bottom" for deeper understanding of pain mechanisms

• Professor open to questions and feedback before the next semester.