1. LAB EXERCISE 17
OLFACTION & TASTE

2. Chemical Senses
Taste (gustatory) and smell (olfaction)
They are interpreted by cerebral cortex and limbic system.
Their chemoreceptors respond to chemicals in aqueous solution
Taste
Taste receptors are excited by food chemicals dissolved in saliva

3. Chemical Senses
Smell
Smell receptors are excited by air-borne chemicals that dissolve in the fluids coating the nasal membrane million receptors
Difficult to research because one smell can involve up to 10,000 odors

4. The Special Senses Learning Outcomes
17-1 Describe the sensory organs of smell,
trace the olfactory pathways to their
destinations in the brain, and explain
the physiological basis of olfactory
discrimination.

5. Smell (Olfaction) Olfactory Organs
Located in nasal cavity on either side of nasal septum
Made up of two layers
Olfactory epithelium
Lamina propria

6. Olfaction (Smell)
9/21/2018
The olfactory epithelium consists of different types of neurons and olfactory glands that are innervated by the facial nerve.
Olfactory glands (Bowman’s)
Produce mucous which aid in dissolving odorants so transduction can occur.
Basal cells = stem cells
Replace receptors monthly
Olfactory receptors
First order neurons with cilia or olfactory hairs that convert stimulus energy into a graded potential
Supporting cells
Columnar epithelium that provide nourishment, support and insulation.
They also detoxify chemicals
Cilia –
Increases surface area and captures chemicals. immobile
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7. Olfactory Pathway
**Cilia pick up the chemicals and move them through the
axons from olfactory receptors
 First Order Neurons
**The 40 or so first order neurons form the right and left
olfactory nerves.
--Cranial nerve I

8. Olfactory Pathway
They pass through foramina in the cribiform plate and synapse in the olfactory bulb where they become second order neurons
 Mitral Cells
**The glomeruli represent a single
aspect of smell.
>They also release GABA to inhibit
mitral cells so that only highly
excitable smells activate the
mitral cells.
**These neurons form the olfactory tract.

9. Olfactory Pathway
Second-order neurons then move to one of three integration centers by communication of interneurons.
**The only sensory information that
reaches the cortex directly without
first synapsing in thalamus
Primary olfactory cortex of temporal
lobe
Conscious awareness of smell begins
2. The hypothalamus
3. The limbic system
Where memory dictates what we will do with the smell
Hippocampus (Past)
Amygdala (Reaction) anger, happy, sad etc.

10. Physiology & Adaptation
Genetic evidence suggests there are hundreds of primary scents and an ability to recognize 10,000 scents.
Adaptation to odors occurs quickly, and the threshold of smell is low: only a few molecules of certain substances need be present in air to be smelled.
Hyposmia
A reduced ability to smell, affects half of those over age 65 and 75% of those over 80. It can be caused by neurological changes, drugs, or the effects of smoking .

11. Upper Nasal Meatus
Middle Nasal Meatus
Inferior Nasal Meatus
Superior Nasal Concha
Middle Nasal Concha
Inferior Nasal Concha
Olfactory Tract
Olfactory Bulb

12. The Special Senses Learning Outcomes
17-2 Describe the sensory organs of taste,
trace the gustatory pathways to their
destinations in the brain, and explain
the physiological basis of gustatory
discrimination.

13. Taste (Gustation) Taste
Provides information about the foods and liquids consumed
Taste Receptors (Gustatory Receptors)
Are distributed on
Tongue
Soft palate
Pharynx
Larynx
Inside cheeks

14. Taste (Gustation) Taste receptors are clustered into taste buds
Associated with epithelial projections (lingual papillae) on superior surface of tongue

15. Taste (Gustation) Three Types of Lingual Papillae Filiform papillae
Provide friction
Do not contain taste buds
Fungiform papillae
Contain five taste buds each
Circumvallate papillae
For V-shape
Contain 100 taste buds each

16. Taste (Gustation) Contain: Basal cells Stem cells Gustatory cells
Extend taste hairs through taste pore
Survive only 10 days before replacement

17. Taste (Gustation) Gustatory Discrimination
Four primary taste sensations
Sweet
Salty
Sour
Bitter

18. Taste (Gustation) Additional Human Taste Sensations Umami
Characteristic of beef/chicken broths and Parmesan cheese
Receptors sensitive to amino acids, small peptides, and nucleotides
Water
Detected by water receptors in the pharynx
Affects hypothalamus and ADH secretion

19. Gustatory Pathway 1. In order to be tasted, a chemical:
Must be dissolved in saliva
Must contact gustatory hairs in the taste bud

20. Gustatory Pathway 2. Binding of the food chemical (taste)
Depolarizes the taste cell membrane, causing release of neurotransmitter
Initiates a generator potential that elicits an action potential

21. Gustatory Pathway Gustatory fibers found in following cranial nerves
*Facial (7)
Serves anterior 2/3 of tongue
Glossopharyngeal (IX)
Serves posterior 1/3 of tongue
Vagus
Serves palate & epiglottis

22. Gustatory Pathway The first order neurons travel to
the solitary nucleus
of the medulla

23. Gustatory Pathway The second order neuron crosses over at medial
lemniscus with other
somatic sensory information
and is relayed to thalamus

24. Gustatory Pathway
After synapsing in the thalamus, it becomes a third order neuron.
Joins with somatic sensory neurons carrying information on touch, pressure & proprioreception
** Also recieves information from the
limbic system

25. Gustatory Pathway The impulse is then routed to
appropriate area of the
gustatory cortex of the insula. **

26. Gustatory Receptors and Pathways
Central processing of gustatory sensations
Conscious perception of taste occurs at the primary sensory cortex
Taste sensation is analyzed with taste-related sensations
“Peppery” or “burning hot” from afferents in
Trigeminal nerve (V)
Complete adaptation in 1 to 5 minutes
Adaptation quickly reduces sensitivity to new tastes

27. Taste (Gustation) Taste Sensitivity
“Tastes” are a combination of the five taste
sensations plus olfaction. (80% smell)
Exhibits significant individual differences
Some conditions are inherited
For example, phenylthiocarbamide (PTC)
70% of Caucasians taste it but 30% do not

28. Taste (Gustation) Taste Sensitivity Other Factors also influence taste
Thermoreceptors,
Mechanoreceptors,
Nociceptors
Texture enhance or detract from taste
Number of taste buds
Begins declining rapidly by age 50