Lecture Notes: Taste and Smell

Introduction

• Topics Covered:
  • Reception and perception of taste
  • Reception and perception of smell
• Key Terms:
  • Tastants: Chemicals tasted
  • Odorants: Chemicals smelled

General Concepts

• Both taste and smell work through chemo receptors.
• Environment: Both processes occur in aqueous environments.
  • Tastants must be dissolved in saliva.
  • Odorants must be dissolved in mucus.
• Most physiological functions occur in aqueous environments.

Taste

Anatomy of Taste

• Tongue Structures:
  • Pilli (Pilla): Nipple-like projections, not taste buds.
  • Taste buds located along the sides of pilli.

Taste Bud Composition

• Types of Epithelial Cells:
  • Stratified Squamous Epithelium: Protective walls.
  • Gustatory Epithelial Cells: Sensors of taste, contain gustatory hairs.
  • Basal Epithelial Cells: Stem cells for regenerating gustatory cells.
• Taste Pore: Opening where tastants enter.

Function of Gustatory Cells

• Depolarization: Tastants cause epithelial cells to depolarize, signal sent to brain.
• Regeneration: Epithelial cells regenerate every 7-10 days.

Types of Taste Sensations

• Sweet: Sugars, saccharin, alcohol.
• Salt: Metal ions (e.g., sodium, potassium).
• Sour: Acids, hydrogen ions.
• Bitter: Alkaloids (e.g., nicotine).
• Umami: Savory flavor from glutamate.

Perception of Taste

• Cranial Nerves Involved:
  • CN VII (Facial nerve)
  • CN IX (Glossopharyngeal nerve)
  • CN X (Vagus nerve)
• Pathway: Taste information -> Solitary nucleus -> Thalamus -> Gustatory cortex, hypothalamus, limbic system.

Smell (Olfaction)

Anatomy of Smell

• Organ of Smell: Olfactory epithelium.
• Location: Superior nasal concha.
• Sniffing Enhances Smell: Directs odorants to the roof of the nasal cavity.

Olfactory Receptor Cells

• Characteristics:
  • Unusual, bipolar neurons.
  • Millions present with radiating cilia.
  • Regeneration every 30-60 days.
• Odorants: Complex, discrete, and cause depolarization with few molecules.

Metabotropic Receptors

• G-Protein Coupled Receptor System:
  • Amplifies signal within cell.
  • Involves receptor, G protein, adenylyl cyclase, cyclic AMP, and ion channels.
  • Sensitive to few odorants.

Perception of Smell

• Cranial Nerve I (Olfactory Nerve):
  • Signals through mitral cells to olfactory cortex.
  • Also sends signals to hypothalamus, amygdala, limbic system.
  • Closely tied to memory and emotion.

Adaptation

• Mechanism:
  • Sodium induces depolarization.
  • Calcium adaptation for habituation to smells.