1. Chapter 17: The Special Senses
Muse Bio 2440
Lecture #4 5/21/13

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. Figure 17-2 Olfactory and Gustatory Receptors
Olfaction and gustation are special senses that provide us with vital information about our environment. Although the sensory information provided is diverse and complex, each special sense originates at receptor cells that may be neurons or specialized receptor cells that communicate with sensory neurons.
Stimulus
Dendrites
Specialized olfactory neuron
Stimulus removed
Action potentials
Stimulus
Threshold
Generator potential
to CNS 11

12. 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.

13. 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

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

15. (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

16. Gustation: Sense of Taste
Taste bud

17. 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

18. Figure 17-3b Gustatory Receptors
Taste buds
Circumvallate papilla
Fungiform papilla
Filiform papillae
The structure and representative locations of the three types of lingual papillae. Taste receptors are located in taste buds, which form pockets in the epithelium of fungiform or circumvillate papillae. 18

19. (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

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

21. 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

22. 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

23. Figure 17-2 Olfactory and Gustatory Receptors
Receptor cell
Stimulus
Stimulus removed
Stimulus
Receptor cell
Threshold
Receptor depolarization
Synapse
Axon of sensory neuron
Axon
Action potentials
Stimulus
Synaptic delay
to CNS
Generator potential 23

24. Figure 17-2 Olfactory and Gustatory Receptors
Salt and Sour Receptors
Sweet, Bitter, and Umami Receptors
Salt receptors and sour receptors are chemically gated ion channels whose stimulation produces depolarization of the cell.
Receptors responding to stimuli that produce sweet, bitter, and umami sensations are linked to G proteins called gustducins (GUST-doos- inz)protein complexes that use second messengers to produce their effects.
Sweet, bitter, or umami
Sour, salt
Gated ion channel
Membrane receptor
Resting plasma membrane
Inactive G protein
Active G protein
Channel opens
Depolarized membrane
Active G protein
Active 2nd messenger
Inactive 2nd messenger
Depolarization of membrane stimulates release of chemical neurotransmitters.
Activation of second messengers stimulates release of chemical neurotransmitters. 24

25. 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.

26. 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.

27. 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

28. Gustatory Pathway

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

30. Actions of the Major Tastants
15-30 30