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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

what is reproduction
smart Reply
it is d act of bringing young ones to life
to ensure survival of a species🚴‍♀️
what is a genotype
what is hazardous
a cell is the smallest unit of a living thing. so we all have cell
It is the formation of a zygote resulting from the fusion of the sperm cell with the ovum.Thus,this results in the production of new species which are genetically dissimilar from their parent cells.
what is size of cell
Mohd Reply
what is size of Hart
nanometers=um sign thingie
monomers and polymers of nucleic acids?
Jyrl Reply
dna and rna involvement
give me the elements of the soil
Iguma Reply
Air, water, organic matter, inorganic matter
soil water humus air
silica, iron
potassium, sulfur, calcium, carbon
what is cell
iyaji Reply
A cell is a smallest fundamental unit of a living organisms.
the basic structural and functional unit of life
what is size of cell
all things are made up of.....all things cannot exist without pre-exisiting cells...check out the 16th ce tury to learn more about microscope use and cells. i will give a hint: Mr. L.
we are all made of cells
Nutrition - sensitive intervention
Therowda Reply
what does the sori In fern mean
arhin Reply
biology is the study .exactly what is life?
i'm sorry , the study of life
how can U identify a person through his blood
Frankyx Reply
through genetic fingerprinting where specific DNA sequences in a person genome can be identified.
by help of genetics and DNA test
can it also be detected using an RNA test
environmental biology
Ojesola Reply
what is phytoplankton
What is anabolism
Treasure Reply
the break down of substance
how many teeth has an adult person
32 teeth
32 (or 36 including the wisdom teeth)
what is homoestastis
Ayo Reply
hypothalamus negative feedback vs. postive feedback systems.
it is the maintenance of a steady internal environment.it is controlled largely by the brain especially the hypothalamus.
What is a cell
Eric Reply
A cell is the building block of all organisms
yes it is , it also helps in functions .
cell is structural & functional unit of oraganisms
it is a building blocks of a living organism
it is the basic unit of life in living organisms
it is the basic unite of life in living organisms
it is the fundamental unit of life
it is the structural and functional unit of life
Why cells are classify as living and non living things
Millicent Reply
due to such as virus which acts as a living cell inside the cell of an organisms and out side of cell in form of crystals
because there are living cells which performs complex processes such as reproduction and metabolism then there are dead cells like the top most part of the epidermis or the bark
because there are living cells which performs complex function such as reproduction and metabolism
cause otherwise you could call fire alive
what's nomenclature
Joseph Reply
assigning scientific name to organism
yes, the genius name, and the species name
it is a scientific naming of organism
why drinking excess alcohol causes thirst and dehydration
uwikuzo Reply

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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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