1. Chapter 17: The Special Senses
Muse Bio 2440
Lecture #4 5/13/10

2. Comparison of General and Special Senses
General Senses
Special Senses
Include somatic sensations (tactile, thermal, pain, and proprioceptive) and visceral sensations.
Scattered throughout the body.
Simple structures.
Include smell, taste, vision, hearing and equilibrium.
Concentrated in specific locations in the head.
Anatomically distinct structures.
Complex neural pathway.

3. Olfaction: Sense of Smell
Olfactory epithelium contains million receptors.
Olfactory receptor- a bipolar neuron with cilia called olfactory hairs.
- Respond to chemical stimulation of an odorant molecule.
Supporting cells- provide support and nourishment.
Basal cells- replace olfactory receptors.

4. Olfactory Epithelium and Olfactory Receptors

5. Olfactory Epithelium and Olfactory Receptors continued…

6. Smell (Olfaction) Olfactory Pathways
Arriving information reaches information centers without first synapsing in thalamus

7. Olfactory epithelium Olfactory tract Olfactory bulb Nasal conchae
Route of
inhaled air
(a)
Figure 15.21a

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

9. Physiology of Olfaction
Can detect about 10,000 different odors.
Odorant binds to the receptor of an olfactory hair→ G-protein activation→ activation of adenylate cyclase→ production of cAMP→ opening of Na+ channels→ inflow of Na+ →generator potential→ nerve impulse through olfactory nerves→ olfactory bulbs→ olfactory tract→ primary olfactory area of the cerebral cortex.

10. Olfactory transduction

11. Summary of sense of smell
Odorant molecule binds one of million receptors.
Conformational change in receptor interacts with G protein
G protein activates adenylate cyclase to generate cAMP
cAMP opens Na+ channels to initiate depolarization.
Information on number of action potentials decoded by olfactory
bulbs.
Animals have greater numbers of receptors thus better sense of smell
Usually 10,000 times greater.

12. Sense of Taste Receptor organs are taste buds Found on the tongue
On the tops of fungiform papillae
On the side walls of foliate papillae and circumvallate (vallate) papillae

13. Circumvallate papilla
Taste bud
(b) Enlarged section of a
circumvallate papilla.
Figure 15.23b

14. (a) Taste buds are associated with fungiform,
Epiglottis
Palatine tonsil
Lingual tonsil
Foliate papillae
Fungiform papillae
(a) Taste buds are associated with fungiform,
foliate, and circumvallate (vallate) papillae.
Figure 15.23a

15. Gustation: Sense of Taste
Taste bud

16. Structure of a Taste Bud
Flask shaped
50–100 epithelial cells:
Basal cells—dynamic stem cells
Gustatory cells—taste cells
Microvilli (gustatory hairs) project through a taste pore to the surface of the epithelium

17. (c) Enlarged view of a taste bud.
Connective
tissue
Gustatory
hair
Taste fibers
of cranial
nerve
Stratified
squamous
epithelium
of tongue
Basal
cells
Gustatory
(taste) cells
Taste
pore
(c) Enlarged view of a taste bud.
Figure 15.23c

18. Taste (Gustation) Gustatory Discrimination Primary taste sensations
Sweet (sugars)
Salty
Sour (acids)
Bitter (alkali)
umami - savory (fat)

19. Taste Sensations - chemical triggers
There are five basic taste sensations
Sweet—sugars, saccharin, alcohol, and some amino acids
Sour—hydrogen ions
Salt—metal ions
Bitter—alkaloids such as quinine and nicotine
Umami—amino acids glutamate and aspartate

20. Taste (Gustation) Gustatory Discrimination
Dissolved chemicals contact taste hairs
Bind to receptor proteins of gustatory cell
Salt and sour receptors
Chemically gated ion channels
Stimulation produces depolarization of cell
Sweet, bitter, and umami stimuli
G proteins: (proteins that bind GTP- secondary messengers)
gustducins

21. Anatomy of Taste Buds and Papillae
Taste bud- made of three types of epithelial cells: supporting cells, gustatory receptor cells and basal cells.
About 50 gustatory cells per taste bud. Each one has a gustatory hair that projects through the taste pore.
Taste buds are found in the papillae.
Three types of papillae: vallate (circumvallate), fungiform and foliate.

22. Physiology of Gustation
Five types of taste: sour, sweet, bitter, salty and umami.
Tastant dissolves in saliva → plasma membrane of gustatory hair→ receptor potential→ nerve impulse via cranial nerves VII, IX and X→ medulla→ thalamus→ primary gustatory area of the cerebral cortex.

23. Influence of Other Sensations on Taste
Taste is 80% smell
Thermoreceptors, mechanoreceptors, nociceptors in the mouth also influence tastes
Temperature and texture enhance or detract from taste

24. Gustatory Pathway

25. Specialist taste buds map to certain regions of tongue
Maps differ somewhat , but generally