Olfactory and taste

Overview

  1. Olfaction involves detecting odorants dissolved in air and nasal mucus through chemoreceptors

  2. Humans can distinguish thousands of different odors

  3. Provides crucial information about food, people, and potential dangers

Olfactory Epithelium

  1. Located in superior region of nasal cavity

  2. Contains three types of cells:

    1. Olfactory receptor cells (detect odorants)

    2. Supporting cells (sustain receptors)

    3. Basal cells (replace olfactory receptor cells)

  3. Olfactory Receptor Cells

    1. Primary neurons in sensory pathway

    2. Bipolar structure with single dendrite and unmyelinated axon

    3. Feature olfactory hairs (cilia) with chemoreceptors for specific odorants

    4. Perceived smell depends on which cells are stimulated

Neural Pathways

  1. Olfactory nerves (CN I) bundle axons and project through cribriform plate

  2. Olfactory bulbs located under frontal lobes

  3. Unique among senses: bypasses thalamus

  4. Projects directly to:

    1. Primary olfactory cortex (temporal lobe)

    2. Hypothalamus

  5. Amygdala

Gustation (Sense of Taste)

  1. Tongue Papillae

    1. Filiform papillae

      1. Located on anterior two-thirds of tongue

      2. No taste buds; helps manipulate food

    2. Fungiform papillae

      1. Mushroom-shaped

      2. Contains few taste buds

      3. Located on tip and sides

    3. Foliate papillae

      1. Leaflike ridges

      2. Present in early childhood

      3. Located on posterior lateral tongue

    4. Vallate papillae

      1. Largest but least numerous

    5. Contains most taste buds

      1. Located in row of 10-12 on posterior dorsal surface

  2. Taste Buds

    1. Onion-shaped organs containing:

    2. Gustatory cells (detect tastants)

    3. Supporting cells

    4. Basal cells (replace gustatory cells)

    5. Gustatory microvilli extend through taste pore to tongue surface

Basic Taste Sensations

  1. Five primary tastes:

    1. Sweet (organic compounds, sugars)

    2. Salt (metal ions like Na+ and K+)

    3. Sour (acids)

    4. Bitter (alkaloids)

    5. Umami (amino acids, savory/meaty)

Neural Pathways for Taste

  1. Anterior tongue: Facial nerve (CN VII)

  2. Posterior tongue: Glossopharyngeal nerve (CN IX)

  3. Signal progression:

    1. Medulla (triggers salivation/stomach secretions)

    2. Thalamus

    3. Primary gustatory cortex

  4. Taste integration with temperature, texture, and smell

  5. Note: Food taste diminishes when olfaction is blocked (e.g., during a cold)

Additional Notes

  1. Children have more taste buds than adults

  2. Cannot taste starch

  3. Taste and smell are closely interconnected sensory systems