Lecture Taste and Smell

Resources Available

  • List of online sources through the library:

    • Berne & Levy Chapter 8: Special Senses (online)

    • Boron & Boulpaep Chapter 15 (online)

  • Recommended Searches:

    • Keywords: taste/gustation or smell/olfaction

Experimental Techniques in Smell Research

  • Suggestions for Investigation:

    • Sniff tests to report sensations.

    • Detection: identifying if a smell is present.

    • Thresholds: measuring the concentration required for detection.

    • Characteristics: evaluating smell attributes (nice, nasty, etc.).

    • Identification: determining if the smell is recognized.

  • Considerations:

    • Shared sensory experiences among individuals?

    • Extension to animal studies.

    • Molecular biology approaches to identify receptor proteins or coding genes.

    • Humans: ~400 types of olfactory receptors.

    • Dogs: 1094 types of olfactory receptors.

    • Performance differences not solely due to the number of receptors.

Factors Affecting Smell Performance

  • Absence of a predictive model for olfactory perception based on receptor activity patterns.

  • Additional Considerations:

    • Area of olfactory epithelium:

      • Dogs: ~170 cm²

      • Humans: ~10 cm²

    • Gas flow patterns across the epithelium (continuous airflow in dogs).

    • Other olfactory organs (e.g., vomeronasal organ in dogs).

    • Comparative volume of the CNS in the olfactory bulb:

      • Dogs: 2% of brain

      • Humans: 0.03% of brain

    • Capacity for learning and interpreting smells via experience.

Human Smell & Taste Pathways

  • Unusual layout of the human olfactory pathway:

    • Olfactory neuron → glomeruli → second-order neurons → olfactory bulb.

  • Is the olfactory bulb classified as part of the cortex?

Human Taste Pathway

  • Overview of tastants and taste buds:

    • Methods of transduction in taste and smell.

    • Odorant binding to olfactory receptors initiates a cascade leading to neuronal activation.

  • Taste Types:

    • Umami's origin in Japanese, linked to glutamate.

    • Dietary impacts of glutamate through the gut-brain axis.

Additional Taste Modalities

  • Pungency: responding to spicy foods (chili, ginger).

  • Coolness: (mint, menthol).

  • Other sensations:

    • Numbness, astringency, metallic taste, and starchiness lack defined receptors.

    • Research showing significance of dietary glutamate in metabolism regulation.

Supertasters

  • Definition: Individuals with heightened taste sensitivities, linked to the gene TAS2R38 (increased bitterness perception).

  • Prevalence: Approximately 25% of individuals identified as supertasters.

  • Discuss the implications of being a supertaster and its impact on diet choice.

Boar Taint

  • Definition: Unpleasant odor in pork from non-castrated male pigs at puberty.

  • Occurrence: Found in about 20% of male pigs.

  • Factors to explore: Variability in odor perception among different individuals.

Transduction Mechanisms: Taste

  • Salt & Sour Tastes:

    • Mechanisms for sour taste involve H+ ion interaction, while salt taste evokes Na+ influx.

  • Sweet, Bitter, Umami Tastes:

    • Stimuli bind to surface receptors → activate G protein → increase intracellular Ca++ → trigger action potentials.

  • Further studies suggested for better understanding of the interplay between taste receptors and hormonal responses to taste stimuli (e.g., CPIR).

Further Considerations Regarding Diabetes

  • Explore expectations of insulin secretion related to sugar intake and the implications of sweet, sugar-free beverages on metabolism.