Lecture on Human Senses and Olfaction

Types of Senses

• General Senses: Distributed throughout the body.
  • Examples: Touch, pain, temperature.
• Special Senses: Detected only by specific organs.
  • Examples: Vision, hearing, equilibrium.
  • Five special senses include:
    • Olfaction (smell)
    • Gustation (taste)
    • Vision
    • Hearing
    • Equilibrium

Olfaction (Sense of Smell)

• Odorants: Molecules that trigger the sense of smell.
• Olfactory Organs: Located in the nose, consist of:
  • Olfactory Epithelium: Outer layer.
  • Lamina Propria: Contains:
    • Areolar tissue (loose connective tissue)
    • Blood vessels
    • Nerves
    • Olfactory glands (produce mucus)

Anatomy of Olfactory Organs

• Olfactory Epithelium: Contains
  • Olfactory Sensory Neurons: aka olfactory receptors, detect odorants.
  • Supporting Cells: Provide structural support.
  • Basal Epithelial Cells: Act as stem cells, replace neurons.
• Process of Smelling:
  • Odorant molecules dissolve in mucus.
  • Bind to receptors on olfactory sensory neurons.
  • Generates a "generator potential."
  • If strong enough, triggers an action potential.
  • Action potentials travel via axons (nerve fibers) to the brain.

Olfactory Pathway

• Olfactory Nerve (Cranial Nerve I): Bundled axons pass through the cribriform plate to the olfactory bulb.
• Olfactory Bulb: First synapse occurs here, located in cerebrum.
• Olfactory Tract: Carries action potentials deeper into the brain.

Brain Regions Involved in Olfaction

• Olfactory Cortex
• Hypothalamus
• Limbic System
  • Regions connected to memory and emotions.

Effects of Smell on Brain

• Smells can trigger memories and emotions due to brain connections.
• Adaptation occurs, reducing sensitivity to persistent odors.

Olfactory Discrimination

• Ability to differentiate and assess intensity of odors.
• Humans can differentiate 2,000 to 4,000 odors.
• Animals like dogs can detect far more.

Sensitivity and Aging

• Sensitivity varies by odorant.
• Decrease in sensitivity with age due to less active basal cells.

Summary

• Olfaction involves complex processes and structures that allow detection and interpretation of smells.
• Plays a crucial role in memory, emotion, and perception.