Pain and Temperature Sensing: Nociception and Thermoception

Key Concepts

• Nociception: The scientific term for sensing pain.
• Thermoception: The scientific term for sensing temperature.
• Both senses rely on specialized receptors called TRPV1 receptors.

TRPV1 Receptors

• Located within the cell membrane of sensory cells throughout the body.
• Sensitive to both temperature changes and painful stimuli.
• Activated by conformational changes in the protein structure.
• Example: Heat or certain molecules can cause these changes.

Mechanism of Action

1. Temperature Change

   • Example: Placing a hand on a stove induces heat.
   • Heat causes a conformational (structural) change in TRPV1 receptor protein.
   • This change activates the receptor, sending a signal to the brain.

2. Painful Stimulus

   • Example: Sharp object poking the hand.
   • Cells break and release molecules upon injury.
   • Molecules (e.g., green molecule) bind to TRPV1 receptors, causing conformational changes.
   • Same activation process sends a pain signal to the brain.

Types of Nerve Fibers

• A-beta fibers (Fast)

  • Large diameter, heavily myelinated.
  • Conduct signals very quickly.
  • Example: Quick hand withdrawal from hot stove.

• A-delta fibers (Medium)

  • Medium diameter, less myelinated.
  • Conduct signals moderately fast.
  • Example: Quick pain sensation after touching a hot stove.

• C fibers (Slow)

  • Small diameter, unmyelinated.
  • Conduct signals slowly.
  • Example: Lingering burning sensation after touching a hot stove.

Example: Jalapeno and Capsaicin

• Eating a jalapeno triggers pain like a hot temperature.
• Jalapeno cells contain capsaicin, which binds to TRPV1 receptors in the tongue.
• Activates the same response as a temperature change, causing sweating and burning sensation.
• Body reacts similarly to capsaicin as it does to heat.

Summary

• Nociception: Sensing pain through TRPV1 receptors.
• Thermoception: Sensing temperature through TRPV1 receptors.
• TRPV1 receptors are activated by temperature changes and molecules like capsaicin.
• Signal transmission to the brain involves different nerve fibers of varying speeds.