1. Copyright © 2010 Pearson Education, Inc. Chemical Senses Chemoreceptors for chemicals in aqueous solution

2. Copyright © 2010 Pearson Education, Inc. Sense of Smell Olfactory epithelium in roof of nasal cavity Olfactory receptor cells with radiating y cilia Axons of olfactory receptor cells form olfactory nerve

3. Copyright © 2010 Pearson Education, Inc. Figure 15.21a Olfactory tract Olfactory bulb (a) Nasal conchae Route of inhaled air Olfactory epithelium

4. Copyright © 2010 Pearson Education, Inc. Figure 15.21a Mitral cell (output cell) Olfactory gland Olfactory tract Olfactory epithelium Filaments of olfactory nerve Cribriform plate of ethmoid bone Lamina propria connective tissue Basal cell Supporting cell Dendrite Olfactory cilia Olfactory bulb Glomeruli Axon Olfactory receptor cell Mucus Route of inhaled air containing odor molecules (b)

5. Copyright © 2010 Pearson Education, Inc. Physiology of Smell Dissolved odorants bind to receptor in cilium membranes causing depolarization of receptor membrane that triggers an AP

6. Copyright © 2010 Pearson Education, Inc. Olfactory Pathway Receptor synapse with mitral cells - amplify and relay signals along olfactory tracts to the: Olfactory cortex Hypothalamus and limbic system

7. Copyright © 2010 Pearson Education, Inc. Figure 15.22 1 2 Odorant binds to its receptor. Receptor activates G protein (G olf ). 3 G protein activates adenylate cyclase. 4 Adenylate cyclase converts ATP to cAMP. 5 cAMP opens a cation channel allowing Na + and Ca 2+ influx and causing depolarization. Odorant G protein (G olf ) Receptor Adenylate cyclase Open cAMP-gated cation channel GDP

8. Copyright © 2010 Pearson Education, Inc. Sense of Taste Taste buds on tongue Top of fungiform papillae Side of foliate papillae and circumvallate (vallate) papillae

9. Copyright © 2010 Pearson Education, Inc. Figure 15.23a (a) Taste buds are associated with fungiform, foliate, and circumvallate (vallate) papillae. Fungiform papillae Epiglottis Palatine tonsil Foliate papillae Lingual tonsil

10. Copyright © 2010 Pearson Education, Inc. Figure 15.23b (b) Enlarged section of a circumvallate papilla. Taste bud Circumvallate papilla

11. Copyright © 2010 Pearson Education, Inc. Structure of a Taste Bud 50–100 epithelial cells: Basal cells—dynamic stem cells Gustatory cells—taste cells Microvilli (gustatory hairs) project through a taste pore

12. Copyright © 2010 Pearson Education, Inc. Figure 15.23c Taste fibers of cranial nerve Connective tissue Gustatory (taste) cells Taste pore Gustatory hair Stratified squamous epithelium of tongue (c) Enlarged view of a taste bud. Basal cells

13. Copyright © 2010 Pearson Education, Inc. Taste Sensations Five basic taste sensations 1.Sweet—sugars, saccharin, alcohol, and some amino acids 2.Sour—hydrogen ions 3.Salt—metal ions 4.Bitter—alkaloids such as quinine and nicotine 5.Umami—amino acids glutamate and aspartate

14. Copyright © 2010 Pearson Education, Inc. Physiology of Taste To be tasted, a chemical: Must dissolve in saliva Contact gustatory hairs Depolarizes membrane, causing release of NT Initiates a generator potential that elicits an action potential

15. Copyright © 2010 Pearson Education, Inc. Taste Transduction The stimulus energy of taste causes gustatory cell depolarization by: Na + influx in salty tastes (directly causes depolarization) H + in sour tastes (by opening cation channels) G protein gustducin in sweet, bitter, and umami tastes (leads to release of Ca 2+ from intracellular stores, which causes opening of cation channels in the plasma membrane)

16. Copyright © 2010 Pearson Education, Inc. Gustatory Pathway Cranial nerves VII and IX carry impulses from taste buds to the solitary nucleus of the medulla Impulses then travel to the thalamus and from there fibers branch to the: Gustatory cortex in the insula Hypothalamus and limbic system (appreciation of taste)

17. Copyright © 2010 Pearson Education, Inc. Figure 15.24 Gustatory cortex (in insula) Thalamic nucleus (ventral posteromedial nucleus) Pons Solitary nucleus in medulla oblongata Facial nerve (VII) Glossopharyngeal nerve (IX) Vagus nerve (X)

18. Copyright © 2010 Pearson Education, Inc. Influence of Other Sensations on Taste Taste is 80% smell Thermoreceptors, mechanoreceptors, nociceptors in mouth influence taste