Lecture Notes: Pheromones and the Olfactory System

Introduction to Pheromones

• Observational example: Dogs peeing on fire hydrants to mark territory.
• Pheromones: Molecules in animal urine that can be detected by other animals.
  • Serve as specialized olfactory cues.
  • Act as chemical signals triggering innate responses in other species members.
• Importance in animals, especially insects, for activities such as mating, fighting, and communication.

Anatomy of the Olfactory System

• Olfactory Epithelium: Sensitive to various molecules, part of the nasal passage.
• Accessory Olfactory Epithelium: Sends projections to the accessory olfactory bulb.
  • Vomeronasal System: Located within the accessory olfactory epithelium.
    • Basal Cells: Send long projections.
    • Apical Cells: Have short projections.

Mechanism of Action

• Pheromone detection involves sensory cells with receptors.
  • Specific molecules (e.g., from dog urine) activate receptors on these cells.
• Signal pathway:
  • Activated cells send axons to the accessory olfactory bulb.
  • Synapse onto a glomerulus, then to a mitral or tufted cell.
  • Axon extends to the brain, specifically the amygdala.

Role of the Amygdala

• Processes emotions, aggression, and mating responses.
• Behaviors can be influenced by pheromonal signals received in the amygdala.

Signal Transduction

• Signal transduction occurs when a molecule binds to a receptor (G-protein-coupled receptor).
• Similar to regular olfaction, leading to cell depolarization and firing.

Human Perspective

• Humans have a vomeronasal organ but lack an accessory olfactory bulb.
• Humans rely less on pheromones compared to other animals.