Special Sense: Smell & Taste

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October 2016
Special Senses: Smell & Taste
Andrew Kosc - 10090720
Ariana Alvarino - 10099976
Sam Wiley - 10141699
Jessica Yeram Kim - 10185221
Ryerson Smylie - N/A

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Smell:
Olfactory Organs & Receptor Cells
Olfactory Discrimination
Olfactory Pathways

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1. Olfactory Receptor Cells 2. Supporting Cells 3. Basal Cells
Olfactory Anatomy
 Nasal cavity
 Olfactory epithelium
 Collection of olfactory receptors lining the nasal cavity
 Wet
 Composed of 3 distinct cell types:
 Olfactory receptor cells, Supporting cells, Basal Cells
Smell: Olfactory Organs & Receptor Cells
• Detects Odors
• Bipolar neurons
(2 processes from
cell body)
• Surrounds olfactory receptor cells
• Insulates olfactory receptor cells
• Regulate composition of the mucus
• Plays a role in deactivating odorants
• Located at the base of the membrane
• Continually divides into olfactory
receptor cells (regenerating;
replacing old cells)
Olfactory Receptor
Cell
Supporting Cell
Basal Cell

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Cilia Olfactory BulbStructural Organization
Smell: Olfactory Organs & Receptor Cells
• Immobile hair-like structure on the
mucus layer
• Traps odorant molecules
• Contains olfactory receptor proteins
o Protein = chain of amino acids
o Variations in sequence of amino
acid in chain -> gives arise to
distinct receptors which are
sensitive to different odorants
• Located in the forebrain
• Axons of olfactory receptor cells
extend and converge in olfactory bulb
• Lamina propria
o Areolar connective tissue
o Under the basement membrane
lining a layer of olfactory
epithelium
• Mucus
o Covers the exterior surface of
the olfactory epithelium
o Secretions of supporting cells
and olfactory glands
• Olfactory mucosa
o Upper region of nasal cavity
o Contains olfactory receptor cells
which has cilia

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Produced by a combination of chemicals and not
detected or recognized by everyone
 No obvious structural differences between olfactory
receptor cells that account for the difference in
recognition ability.
 However, as a person ages, their ability to recognize
odor decreases and they begin to lack discrimination.
Secondary Odors
Detectable by a large number of people
 Aromas are amalgams of a mixture of these odors.
 Our appreciation and comprehension of smells are
the result of such processes as developing an
“acquired taste” for something.
Primary Odors
Olfactory Discrimination
The olfactory system can recognize as many as eight different primary odors, as well as thousands of other chemical stimuli.

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Pathway
Olfactory Pathways
Diagram Cadaveric View
• Olfactory stimuli do not immediately project to the
thalamus. Instead, they travel to the olfactory cortex in the
temporal lobe.
• Later, olfactory sensations can project from the temporal
lobes to the thalamus, and then to the frontal lobes for
more specific discrimination.
• However, there are widespread olfactory associations
within the hypothalamus and limbic system.
• Olfactory nerve axons (discrete bundles of olfactory
neuron axons) projects through foramina in the cribriform
plate and enter a pair of olfactory bulbs inferior to the
frontal lobes of the brain.
• Neurons within the olfactory bulbs project axon bulbs
(called olfactory tracts) to the primary olfactory cortex in
the temporal lobe of the cerebrum.

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QUESTION:
Why can’t we smell when we get nose congestion? What structures
may be involved in it (which part is damaged/affected)?

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Taste:
Papillae & Taste Buds
Gustatory Discrimination
Gustatory Pathways

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 Each cylindrical taste bud is composed of gustatory
cells, which are enclosed by supporting cells.
 The gustatory microvillus extends through an
opening in the taste bud, and is the receptive
portion of the cell.
 The gustatory cells within taste buds are specialized
neuroepithelial cells that have a 7-10-day life span.
 Basal cells constantly replace gustatory cells
(replacement slows down at around age 50)
 Filiform papillae: detect texture and manipulate food
 Fungiform papillae: contain only a few taste buds
 Vallate palillae: least numerous yet largest
 Foliate papillae: only few taste buds during infancy
Papillae
Taste Buds
Basal Cells
Highlights
On the surface of the tongue are epithelial and connective tissue elevations called papillae.
There are four types of papillae: filiform, fungiform, vallate, and foliate
Taste: Papillae & Taste Buds of the Tongue

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• In contrast to the large number of olfactory receptors we have in our nose, our tongue detects just five basic taste sensations:
• Bitter tastes are produced primarily by alkaloids such as quinine, unsweetened chocolate, nicotine, and caffeine.
• Salty tastes are produced by metal ions, such as sodium (Na+) and potassium (K+).
• Sweet tastes are produced by organic compounds such as sugar or other molecules (e.g., artificial sweeteners).
• Sour tastes are associated with acids in the ingested material, such as hydrogen ions (H+) in vinegar.
• Umami stimuli: Umami is a Japanese word meaning “delicious flavor.” It is a taste related to amino acids, such as glutamate and
aspartate, to produce a meaty flavor.
• A combination of taste sensations allows the human body to be exposed to a wide variety of tastes.
• Our taste receptors are more sensitive to sour and bitter stimuli, as those sensations are commonly found in toxic and poisonous food.
Taste: Gustatory Discrimination

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When the gustatory cells detect sensory stimuli, the
information is sent through facial and glossopharyngeal
cranial nerves by nerve impulses
Taste: Gustatory Pathways
The human consciousness then perceives taste by
integrating it with smell, temperature and texture.
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Tertiary neurons then travel from the thalamus to the
primary gustatory cortex, located in the insula of the
cerebrum for analysis
Secondary neurons then send information from the
nucleus solitarius to the thalamus
• A small structure within the brain located directly
above the brainstem.
Gustatory information is then sent to the nucleus solitarius
by primary neurons
• A group of cells in the medulla oblongota (forms lowest
part of brain stem) that receives taste sensations from
the cranial nerves.

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QUESTION:
In what ways are the processes associated with smell and taste similar,
and in what ways are they different?

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Appendices
Booth, I. (2013). Special Senses – Smell, Taste, and Hearing. Retrieved October 18, 2016 from http://slideplayer.com/slide/4525768/
Boroditsky, L. (1999, July 27). Taste, Smell and Touch. Retrieved October 18, 2016 from
http://www-psych.stanford.edu/~lera/psych115s/notes/lecture11/
Innerbody. (2016). Tongue and Taste. HowToMedia Inc. Retrieved October 18th, 2016, from
http://www.innerbody.com/image_nerv12/dige12.html
Intelligent Dental. (2011). Types of Papillae on Tongue. Intelligent Dental Copyright. Retrieved October 18th, 2016, from
http://www.intelligentdental.com/2011/12/18/types-of-papillae-on-tongue/
Ken Hub. (2016). Solitary Tract and Nucleus - Anatomy and Function. Ken Hub Online. Retrieved October 18th, 2016, from
https://www.kenhub.com/en/library/anatomy/the-solitary-tract-and-nucleus
McKinley, P. M., O’Loughlin, D. V., Pennefather-O’Brien, E. E., & Harris, T. R. Human Anatomy. (2015). Human Anatomy 4a. McGraw Hill
Education.
Molnar, C., and Gair, J. (2013). Concepts of Biology. Retrieved October 18, 2016 from
https://opentextbc.ca/biology/chapter/17-3-taste-and-smell/
News Medical. (2016). What is the Thalamus?. Retrieved October 21, 2016, from
http://www.news-medical.net/health/What-is-the Thalamus.aspx
UT Health Science Center. (2014, March 18). Nerve. Retrieved October 18, 2016 from
http://ice.uthscsa.edu/dentalhistologyprepcourse/09%20nerve/Nerve_print.html