1. Special Senses
Olfaction & Gustation

2. Introduction We know what we know because of sensory receptors
Our perceptions governs our interpretation of reality
Perception depends on state of nervous system
We get this information through 5 special senses
Olfaction
Gustation
Vision
Equilibrium
Hearing

3. Olfaction – Sense of Smell
Olfactory organs work together to perceive smell
Organs are located in nasal cavity
Contains olfactory epithelium  olfactory receptors
Contains a second layer, “lamina propria”  olfactory glands

5. Olfactory Receptors Highly modified neurons
Only neurons that routinely regenerate!

7. Olfactory Pathways
Olfactory receptors  olfactory bulbs of the cerebum  olfactory tract  olfactory cortex, hypothalamus, and limbic system
This is why smells are often able to illicit emotions or memory recall
Only type of sensory information that reaches the cerebral cortex directly (does not go to the Thalamus relay center first)

8. Discriminating Smells
Humans can detect over 20,000 kinds of smells
The pattern of receptor binding and activity is what causes a particular perception of smell
Due to the sensitivity of receptors, some odorants can be detected in tiny concentrations
Ex. Mercaptan added to natural gas

9. Gustation – Sense of Taste
Provides information about the foods and liquids we ingest
Gustatory receptors are distributed over the tongue and parts of throat
Taste buds = taste receptors + specialized epithelial cells
Epithelial projections  lingual papillae
Filiform
Fungiform
Vallate
Foliate

10. Filiform Papillae
Provide friction that helps tongue move objects around in the mouth
Most common type
No taste buds

11. Fungiform Papillae
Involved in the sensation of taste and have taste buds embedded in their surfaces
Mostly found on tips and sides of tongues

12. Vallate Papillae Contain tastebuds
Lie near posterior tongue in a V- formation

13. Foliate Papillae
Located on sides and back of tongue

14. Taste Receptors Humans have about 10,000 taste buds
Each taste bud has about receptor cells and basal cells
Receptors are innervated by sensory neurons

15. Gustatory Pathways
Cranial nerves 8, 9, and 10 innervate the taste buds
CN 8 (facial)  taste buds located on anterior 2/3 of the tongue
CN 9 (glossopharangyeal)  innervates the vallate papillae and posterior 1/3 of tongue
CN 10 (vagus)  innervate tastebuds scattered on the epiglottis
Cranial nerves  medulla oblangata
Neurons join there to carry sensory information on touch, pressure, and sense of movement
The gustatory information is finally relayed to the relay center  thalamus

16. Gustatory Pathways
Brain correlates information received from taste buds with other sensory data
Texture of food and taste-related sensations (hot, cold, spicy)  relayed by the trigeminal nerve (CN 5)
Olfactory receptors also a play a role in taste perception!

17. Gustatory Discrimination
Primary taste sensations: sweet, salty, sour, and bitter
Other sensations found in humans: water and umami

18. Umami Pleasant, savory taste Ex. Chicken broth, parmesan cheese
Presence of free glutamates in food

19. Water
Some vertebrate species contain receptors for water in the pharynx
Information is processed by hypothalamus which then regulates water balance and blood volume in the body
Ex. Fluctuations in ADH after drinking lots of water!

20. Gustation Reception
Receptors respond more readily to unpleasant stimuli – essential for survival
Taste sensitivity also varies among people and can be inherited
Ex. Phenylthicarbamide (PTC) – tastes bitter to some people, but tasteless to others. Not found in food. But related compounds found in cauliflower, cabbage, broccoli
Taste receptors, just like smell receptors, decline with age

21. Due Next Week
Ch. 28