1. Gustation and Olfaction (Taste and Smell) chemoreceptors –chemical substance dissolved in mucus –G-protein-linked receptors all smell some taste –sweet –bitter –umami (e.g., glutamate) –channel-linked receptors some taste –sour –salt Rhoades and Pflanzer, Human Physiology cf. Fig. 10-6 Ganong

2. Taste gustatory cells –located in taste buds of the tongue also of the pharynx, epiglottis and soft palate –about 50 - 100 per bud –hairs are microvilli Fig. 16.6

3. Taste 5 (or 6) Taste Modalities received from all parts of the tongue –sour H + –salt ions, especially Na + & Cl - –sweet various organic substances –sucrose –phenylalanine Pb –bitter various organic substances –alkaloids –many drugs –umami / savory: a fifth taste glutamate –fat: a sixth taste? long chain fatty acids (via the CD36 receptor) J. Clin. Invest. 115:3177-3184 (2005)

4. Neural Pathways Neural pathways –facial (VII) and glossopharyngeal (IX) nerves  –medulla and thalamus  –parietal lobe and insula Ganong, 20 th edition Fig. 10-5 Ganong

5. Smell Olfactory cells are bipolar neurons –axons form olfactory nerve –cribriform plate of ethmoid bone roof of nasal cavity floor of skull Fig. 16.7

6. Smell Sniffing increases air flow to roof of nasal cavity. able to distinguish between thousands of different smells –total number of smell modalities not known –Different smells produce different patterns of stimulation on different populations of olfactory receptors. Smell contributes significantly to the “taste” of food.

7. Olfactory Pathway olfactory nerves (sensory)  olfactory tract (mixed)  temporal lobe portions of limbic system –thalamic relay NOT required –Smells can rapidly trigger emotional responses. pheromones –a chemical released by one animal that produces an emotional/behavioral response in another animal –probably exist in humans may work via olfactory system Fig. 16.8