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By the end of this section, you will be able to:
  • Explain in what way smell and taste stimuli differ from other sensory stimuli
  • Identify the five primary tastes that can be distinguished by humans
  • Explain in anatomical terms why a dog’s sense of smell is more acute than a human’s

Taste, also called gustation    , and smell, also called olfaction    , are the most interconnected senses in that both involve molecules of the stimulus entering the body and bonding to receptors. Smell lets an animal sense the presence of food or other animals—whether potential mates, predators, or prey—or other chemicals in the environment that can impact their survival. Similarly, the sense of taste allows animals to discriminate between types of foods. While the value of a sense of smell is obvious, what is the value of a sense of taste? Different tasting foods have different attributes, both helpful and harmful. For example, sweet-tasting substances tend to be highly caloric, which could be necessary for survival in lean times. Bitterness is associated with toxicity, and sourness is associated with spoiled food. Salty foods are valuable in maintaining homeostasis by helping the body retain water and by providing ions necessary for cells to function.

Tastes and odors

Both taste and odor stimuli are molecules taken in from the environment. The primary tastes detected by humans are sweet, sour, bitter, salty and umami. The first four tastes need little explanation. The identification of umami    as a fundamental taste occurred fairly recently—it was identified in 1908 by Japanese scientist Kikunae Ikeda while he worked with seaweed broth, but it was not widely accepted as a taste that could be physiologically distinguished until many years later. The taste of umami, also known as savoriness, is attributable to the taste of the amino acid L-glutamate. In fact, monosodium glutamate, or MSG, is often used in cooking to enhance the savory taste of certain foods. What is the adaptive value of being able to distinguish umami? Savory substances tend to be high in protein.

All odors that we perceive are molecules in the air we breathe. If a substance does not release molecules into the air from its surface, it has no smell. And if a human or other animal does not have a receptor that recognizes a specific molecule, then that molecule has no smell. Humans have about 350 olfactory receptor subtypes that work in various combinations to allow us to sense about 10,000 different odors. Compare that to mice, for example, which have about 1,300 olfactory receptor types, and therefore probably sense more odors. Both odors and tastes involve molecules that stimulate specific chemoreceptors. Although humans commonly distinguish taste as one sense and smell as another, they work together to create the perception of flavor. A person’s perception of flavor is reduced if he or she has congested nasal passages.

Reception and transduction

Odorants (odor molecules) enter the nose and dissolve in the olfactory epithelium, the mucosa at the back of the nasal cavity (as illustrated in [link] ). The olfactory epithelium    is a collection of specialized olfactory receptors in the back of the nasal cavity that spans an area about 5 cm 2 in humans. Recall that sensory cells are neurons. An olfactory receptor    , which is a dendrite of a specialized neuron, responds when it binds certain molecules inhaled from the environment by sending impulses directly to the olfactory bulb of the brain. Humans have about 12 million olfactory receptors, distributed among hundreds of different receptor types that respond to different odors. Twelve million seems like a large number of receptors, but compare that to other animals: rabbits have about 100 million, most dogs have about 1 billion, and bloodhounds—dogs selectively bred for their sense of smell—have about 4 billion. The overall size of the olfactory epithelium also differs between species, with that of bloodhounds, for example, being many times larger than that of humans.

Questions & Answers

by what proces do ameaba reproduce?
Okello Reply
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Janet
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Okello
Hi
Muah
hello
Bob
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Mathew
hi
promise
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promise
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Mary Reply
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Mary
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Mary
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Rachel
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Izzati
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Izzati
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Izzati
what is active transport
Amona Reply
is the movement's of water & mineral salts from the reason of highly concentrated to the reason of low concentration across semi permeable membrane & it take place in plant
Okello
in what situation would the use of a scanning microscope be ideal and why?
Anthony Reply
what is euglina
Ruth Reply
no idea
Enock
Which of the following statements regarding membrane transport is false? 1. Glucose is transported only by facilitated diffusion 2.Each protein carrier will only bind and b transport one type of solute.
#2. Each protein carrier will only bind and b transport one type of soluble
Only
#2 is false for the regarding membrane transport.
Only
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what is gene
Okello Reply
what is somatic cell
garaadmaxamed Reply
what is Biology?
garaadmaxamed
is the study of living things
garaadmaxamed
what is organ
Chan
what is biology
Isiaka Reply
is the study of all living things
Motinga
and their interactions with each other and the environment
Angela
it is the study of all living organisms and their characteristics
ketchem
the study of living things and their surroundings
Ade
what's is biology
Mohamed Reply
what's is dna
Mohamed
deoxybonucliec acid
Gibril
explain the osomor regulations in amoeba and paramecium
Adannaya Reply
explain the osimoregulation in man
Adannaya
who can explain the osmoregulation in amoeba and in man
Adannaya
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Sitali Reply
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Sitali
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Memiru
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Rorisang
what is meant by submicroscopic?
anji Reply
what is anabolic and catabolic
Jonathan
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Alpha
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Memiru
hallo
Memiru
Hello everyone how are you and How's your morning
Chan
what is the meaning of biology
Dorathy Reply
biology is scientific study of living things
GUYO
what is chromosomes?
Mabiya Reply
it is a cell structure that contains DNA histones protein and other structural proteins
Ekechi
what is DNA
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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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