{"id":4902,"date":"2015-10-28T15:55:59","date_gmt":"2015-10-28T15:55:59","guid":{"rendered":"https:\/\/opentextbc.ca\/biology\/chapter\/17-3-taste-and-smell\/"},"modified":"2021-03-04T00:07:42","modified_gmt":"2021-03-04T00:07:42","slug":"17-3-taste-and-smell","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/biology\/chapter\/17-3-taste-and-smell\/","title":{"raw":"17.3 Taste and Smell","rendered":"17.3 Taste and Smell"},"content":{"raw":"<div class=\"titlepage\">\n<div class=\"abstract\">\n<div class=\"bcc-box bcc-highlight\">\n<h3>Learning Objectives<\/h3>\nBy the end of this section, you will be able to:\n<div class=\"itemizedlist\">\n<ul class=\"itemizedlist\">\n \t<li class=\"listitem\">Explain in what way smell and taste stimuli differ from other sensory stimuli<\/li>\n \t<li class=\"listitem\">Identify the five primary tastes that can be distinguished by humans<\/li>\n \t<li class=\"listitem\">Explain in anatomical terms why a dog\u2019s sense of smell is more acute than a human\u2019s<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44764-fs-idp73950336\"> <\/span>Taste, also called <strong><span id=\"m44764-autoid-cnx2dbk-id1839964\"> <\/span>gustation<\/strong>, and smell, also called <span id=\"m44764-autoid-cnx2dbk-id1839968\"> <\/span><strong>olfaction<\/strong>, 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\u2014whether potential mates, predators, or prey\u2014or 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.\n<div class=\"section\" title=\"Tastes and Odors\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44764-fs-idp117278560\" style=\"text-align: left;\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Tastes and Odors<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44764-fs-idp155682448\"> <\/span>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 <span id=\"m44764-autoid-cnx2dbk-id1839996\"> <\/span><strong>umami<\/strong> as a fundamental taste occurred fairly recently\u2014it 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.\n\n<span id=\"m44764-fs-idp247695328\"> <\/span>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\u2019s perception of flavor is reduced if he or she has congested nasal passages.\n\n<\/div>\n<div class=\"section\" title=\"Reception and Transduction\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h3 id=\"m44764-fs-idp10916192\" style=\"text-align: left;\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Reception and Transduction<\/span><\/span><\/h3>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44764-fs-idp174530608\"> <\/span><span id=\"m44764-autoid-cnx2dbk-id1834540\"> <\/span><strong>Odorants<\/strong> (odor molecules) enter the nose and dissolve in the olfactory epithelium, the mucosa at the back of the nasal cavity (as illustrated in <a class=\"xref target-figure\" title=\"Figure\u00a036.8.\u00a0\" href=\"#attachment_1195\">Figure 17.8<\/a>). The <strong><span id=\"m44764-autoid-cnx2dbk-id1834552\"> <\/span>olfactory epithelium<\/strong> is a collection of specialized olfactory receptors in the back of the nasal cavity that spans an area about 5 cm<sup>2<\/sup> in humans. Recall that sensory cells are neurons. An <strong><span id=\"m44764-autoid-cnx2dbk-id1834560\"> <\/span>olfactory receptor<\/strong>, 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\u2014dogs selectively bred for their sense of smell\u2014have 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.\n\n<span id=\"m44764-fs-idp93385696\"> <\/span>Olfactory neurons are <span id=\"m44764-autoid-cnx2dbk-id1827615\"> <\/span><strong>bipolar neurons<\/strong> (neurons with two processes from the cell body). Each neuron has a single dendrite buried in the olfactory epithelium, and extending from this dendrite are 5 to 20 receptor-laden, hair-like cilia that trap odorant molecules. The sensory receptors on the cilia are proteins, and it is the variations in their amino acid chains that make the receptors sensitive to different odorants. Each olfactory sensory neuron has only one type of receptor on its cilia, and the receptors are specialized to detect specific odorants, so the bipolar neurons themselves are specialized. When an odorant binds with a receptor that recognizes it, the sensory neuron associated with the receptor is stimulated. Olfactory stimulation is the only sensory information that directly reaches the cerebral cortex, whereas other sensations are relayed through the thalamus.\n\n[caption id=\"attachment_1195\" align=\"aligncenter\" width=\"400\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_36_03_01.jpg\"><img class=\"wp-image-4897\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_36_03_01.jpg\" alt=\"Figure_36_03_01\" width=\"400\" height=\"278\"><\/a> Figure 17.8.\u00a0 In the human olfactory system, (a) bipolar olfactory neurons extend from (b) the olfactory epithelium, where olfactory receptors are located, to the olfactory bulb. (credit: modification of work by Patrick J. Lynch, medical illustrator; C. Carl Jaffe, MD, cardiologist)[\/caption]\n\n<div id=\"m44764-fig-ch36_03_01\" class=\"figure\" title=\"Figure\u00a036.8.\u00a0\">\n<div class=\"title\"><\/div>\n<div id=\"m44764-fs-idp59413024\" class=\"note evolution\">\n<div class=\"title\">\n<div class=\"body\">\n<h2 class=\"title\">Pheromones<\/h2>\n<p title=\"Pheromones\">A <span id=\"m44764-autoid-cnx2dbk-id1820576\"> <\/span><strong>pheromone<\/strong> is a chemical released by an animal that affects the behavior or physiology of animals of the same species. Pheromonal signals can have profound effects on animals that inhale them, but pheromones apparently are not consciously perceived in the same way as other odors. There are several different types of pheromones, which are released in urine or as glandular secretions. Certain pheromones are attractants to potential mates, others are repellants to potential competitors of the same sex, and still others play roles in mother-infant attachment. Some pheromones can also influence the timing of puberty, modify reproductive cycles, and even prevent embryonic implantation. While the roles of pheromones in many nonhuman species are important, pheromones have become less important in human behavior over evolutionary time compared to their importance to organisms with more limited behavioral repertoires.<\/p>\n<span id=\"m44764-fs-idp259638128\"> <\/span>The vomeronasal organ (VNO, or Jacobson\u2019s organ) is a tubular, fluid-filled, olfactory organ present in many vertebrate animals that sits adjacent to the nasal cavity. It is very sensitive to pheromones and is connected to the nasal cavity by a duct. When molecules dissolve in the mucosa of the nasal cavity, they then enter the VNO where the pheromone molecules among them bind with specialized pheromone receptors. Upon exposure to pheromones from their own species or others, many animals, including cats, may display the flehmen response (shown in <a class=\"xref target-figure\" title=\"Figure\u00a036.9.\u00a0\" href=\"#attachment_1196\">Figure 17.9<\/a>), a curling of the upper lip that helps pheromone molecules enter the VNO.\n\n<span id=\"m44764-fs-idp48589024\"> <\/span>Pheromonal signals are sent, not to the main olfactory bulb, but to a different neural structure that projects directly to the amygdala (recall that the amygdala is a brain center important in emotional reactions, such as fear). The pheromonal signal then continues to areas of the hypothalamus that are key to reproductive physiology and behavior. While some scientists assert that the VNO is apparently functionally vestigial in humans, even though there is a similar structure located near human nasal cavities, others are researching it as a possible functional system that may, for example, contribute to synchronization of menstrual cycles in women living in close proximity.\n\n[caption id=\"attachment_1196\" align=\"aligncenter\" width=\"544\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_36_03_02.jpg\"><img class=\"size-full wp-image-4898\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_02.jpg\" alt=\"Figure\u00a036.9.\u00a0 The flehmen response in this tiger results in the curling of the upper lip and helps airborne pheromone molecules enter the vomeronasal organ. (credit: modification of work by &quot;chadh&quot;\/Flickr)\" width=\"544\" height=\"361\"><\/a> Figure 17.9.\u00a0<br>The flehmen response in this tiger results in the curling of the upper lip and helps airborne pheromone molecules enter the vomeronasal organ. (credit: modification of work by \"chadh\"\/Flickr)[\/caption]\n\n<div id=\"m44764-fig-ch36_03_02\" class=\"figure\" title=\"Figure\u00a036.9.\u00a0\">\n<div class=\"body\">\n<div class=\"mediaobject\"><\/div>\n<\/div>\n<div class=\"title\"><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Taste\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44764-fs-idp3213952\" style=\"text-align: left;\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Taste<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44764-fs-idp10779888\"> <\/span>Detecting a taste (gustation) is fairly similar to detecting an odor (olfaction), given that both taste and smell rely on chemical receptors being stimulated by certain molecules. The primary organ of taste is the taste bud. A <em class=\"glossterm\"><span id=\"m44764-autoid-cnx2dbk-id1828577\"> <\/span>taste bud<\/em> is a cluster of gustatory receptors (taste cells) that are located within the bumps on the tongue called <em class=\"glossterm\"><span id=\"m44764-autoid-cnx2dbk-id1828581\"> <\/span>papillae<\/em> (singular: papilla) (illustrated in <a class=\"xref target-figure\" title=\"Figure\u00a036.10.\u00a0\" href=\"#attachment_1197\">Figure 17.10<\/a>). There are several structurally distinct papillae. Filiform papillae, which are located across the tongue, are tactile, providing friction that helps the tongue move substances, and contain no taste cells. In contrast, fungiform papillae, which are located mainly on the anterior two-thirds of the tongue, each contain one to eight taste buds and also have receptors for pressure and temperature. The large circumvallate papillae contain up to 100 taste buds and form a V near the posterior margin of the tongue.\n\n[caption id=\"attachment_1197\" align=\"aligncenter\" width=\"600\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_36_03_03.jpg\"><img class=\"wp-image-4899\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_03-1024x375-1.jpg\" alt=\"Figure_36_03_03\" width=\"600\" height=\"220\"><\/a> Figure 17.10.\u00a0 (a) Foliate, circumvallate, and fungiform papillae are located on different regions of the tongue. (b) Foliate papillae are prominent protrusions on this light micrograph. (credit a: modification of work by NCI; scale-bar data from Matt Russell)[\/caption]\n\n<div id=\"m44764-fig-ch36_03_03\" class=\"figure\" title=\"Figure\u00a036.10.\u00a0\">\n<div class=\"title\"><\/div>\n<span id=\"m44764-fs-idp21293008\"> <\/span>In addition to those two types of chemically and mechanically sensitive papillae are foliate papillae\u2014leaf-like papillae located in parallel folds along the edges and toward the back of the tongue, as seen in the Figure<a class=\"xref target-figure\" title=\"Figure\u00a036.10.\u00a0\" href=\"ch36.html#m44764-fig-ch36_03_03\"> 17.10<\/a> micrograph. Foliate papillae contain about 1,300 taste buds within their folds. Finally, there are circumvallate papillae, which are wall-like papillae in the shape of an inverted \u201cV\u201d at the back of the tongue. Each of these papillae is surrounded by a groove and contains about 250 taste buds.\n\n<span id=\"m44764-fs-idp99348000\"> <\/span>Each taste bud\u2019s taste cells are replaced every 10 to 14 days. These are elongated cells with hair-like processes called microvilli at the tips that extend into the taste bud pore (illustrate in <a class=\"xref target-figure\" title=\"Figure\u00a036.11.\u00a0\" href=\"#attachment_1198\">Figure 17.11<\/a>). Food molecules (<strong>tastants<\/strong>) are dissolved in saliva, and they bind with and stimulate the receptors on the microvilli. The receptors for tastants are located across the outer portion and front of the tongue, outside of the middle area where the filiform papillae are most prominent.\n\n[caption id=\"attachment_1198\" align=\"aligncenter\" width=\"500\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_36_03_04.jpg\"><img class=\"wp-image-4900\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_04-1024x842-1.jpg\" alt=\"Figure_36_03_04\" width=\"500\" height=\"411\"><\/a> Figure 17.11.\u00a0 Pores in the tongue allow tastants to enter taste pores in the tongue. (credit: modification of work by Vincenzo Rizzo)[\/caption]\n\n<div id=\"m44764-fig-ch36_03_04\" class=\"figure\" title=\"Figure\u00a036.11.\u00a0\">\n<div class=\"title\"><\/div>\n<span id=\"m44764-fs-idp69036720\"> <\/span>In humans, there are five primary tastes, and each taste has only one corresponding type of receptor. Thus, like olfaction, each receptor is specific to its stimulus (tastant). Transduction of the five tastes happens through different mechanisms that reflect the molecular composition of the tastant. A salty tastant (containing NaCl) provides the sodium ions (Na<sup>+<\/sup>) that enter the taste neurons and excite them directly. Sour tastants are acids and belong to the thermoreceptor protein family. Binding of an acid or other sour-tasting molecule triggers a change in the ion channel and these increase hydrogen ion (H<sup>+<\/sup>) concentrations in the taste neurons, thus depolarizing them. Sweet, bitter, and umami tastants require a G-protein coupled receptor. These tastants bind to their respective receptors, thereby exciting the specialized neurons associated with them.\n\n<span id=\"m44764-fs-idp67938160\"> <\/span>Both tasting abilities and sense of smell change with age. In humans, the senses decline dramatically by age 50 and continue to decline. A child may find a food to be too spicy, whereas an elderly person may find the same food to be bland and unappetizing.\n<div id=\"m44764-fs-idp33174096\" class=\"note interactive\">\n<h2 class=\"title\"><span class=\"cnx-gentext-tip-t\">Concept in Action\n<\/span><\/h2>\n<div class=\"body\">\n<div class=\"mediaobject\"><span id=\"m44764-fs-idp261625104\"> <\/span><img src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/taste.png\" alt=\"QR Code representing a URL\" width=\"120\"><\/div>\n<span id=\"m44764-fs-idp128664496\"> <\/span>View this <a class=\"link\" href=\"http:\/\/openstaxcollege.org\/l\/taste\" target=\"\" rel=\"noopener noreferrer\">animation<\/a> that shows how the sense of taste works.\n\n<\/div>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Smell and Taste in the Brain\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44764-fs-idp19236672\" style=\"text-align: left;\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Smell and Taste in the Brain<\/span><\/span><span id=\"m44764-fs-idp79944432\"><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\nOlfactory neurons project from the olfactory epithelium to the olfactory bulb as thin, unmyelinated axons. The <span id=\"m44764-autoid-cnx2dbk-id1831547\"> <\/span><strong>olfactory bulb<\/strong> is composed of neural clusters called <span id=\"m44764-autoid-cnx2dbk-id1831550\"> <\/span><strong>glomeruli<\/strong>, and each glomerulus receives signals from one type of olfactory receptor, so each glomerulus is specific to one odorant. From glomeruli, olfactory signals travel directly to the olfactory cortex and then to the frontal cortex and the thalamus. Recall that this is a different path from most other sensory information, which is sent directly to the thalamus before ending up in the cortex. Olfactory signals also travel directly to the amygdala, thereafter reaching the hypothalamus, thalamus, and frontal cortex. The last structure that olfactory signals directly travel to is a cortical center in the temporal lobe structure important in spatial, autobiographical, declarative, and episodic memories. Olfaction is finally processed by areas of the brain that deal with memory, emotions, reproduction, and thought.\n\n<span id=\"m44764-fs-idp93151360\"> <\/span>Taste neurons project from taste cells in the tongue, esophagus, and palate to the medulla, in the brainstem. From the medulla, taste signals travel to the thalamus and then to the primary gustatory cortex. Information from different regions of the tongue is segregated in the medulla, thalamus, and cortex.\n<h2>Summary<\/h2>\nThere are five primary tastes in humans: sweet, sour, bitter, salty, and umami. Each taste has its own receptor type that responds only to that taste. Tastants enter the body and are dissolved in saliva. Taste cells are located within taste buds, which are found on three of the four types of papillae in the mouth.\n\n<span id=\"m44764-fs-idp132349712\"> <\/span>Regarding olfaction, there are many thousands of odorants, but humans detect only about 10,000. Like taste receptors, olfactory receptors are each responsive to only one odorant. Odorants dissolve in nasal mucosa, where they excite their corresponding olfactory sensory cells. When these cells detect an odorant, they send their signals to the main olfactory bulb and then to other locations in the brain, including the olfactory cortex.\n<div class=\"section\" title=\"Higher Processing\">\n<div class=\"note interactive\">\n<div class=\"body\">\n<div class=\"glossary\" title=\"Glossary\">\n<div class=\"titlepage\">\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<ol>\n \t<li>Which of the following has the fewest taste receptors?\n<ol>\n \t<li>fungiform papillae<\/li>\n \t<li>circumvallate papillae<\/li>\n \t<li>foliate papillae<\/li>\n \t<li>filiform papillae<\/li>\n<\/ol>\n<\/li>\n \t<li>How many different taste molecules do taste cells each detect?\n<ol>\n \t<li>one<\/li>\n \t<li>five<\/li>\n \t<li>ten<\/li>\n \t<li>It depends on the spot on the tongue<\/li>\n<\/ol>\n<\/li>\n \t<li>Salty foods activate the taste cells by ______.\n<ol>\n \t<li>exciting the taste cell directly<\/li>\n \t<li>causing hydrogen ions to enter the cell<\/li>\n \t<li>causing sodium channels to close<\/li>\n \t<li>binding directly to the receptors<\/li>\n<\/ol>\n<\/li>\n \t<li>All sensory signals except _____ travel to the _____ in the brain before the cerebral cortex.\n<ol>\n \t<li>vision; thalamus<\/li>\n \t<li>olfaction; thalmus<\/li>\n \t<li>vision; cranial nerves<\/li>\n \t<li>olfaction; cranial nerves<\/li>\n<\/ol>\n<\/li>\n \t<li>From the perspective of the recipient of the signal, in what ways do pheromones differ from other odorants?<\/li>\n \t<li>What might be the effect on an animal of not being able to perceive taste?<\/li>\n<\/ol>\n<strong>Answers<\/strong>\n<ol>\n \t<li>D<\/li>\n \t<li>A<\/li>\n \t<li>A<\/li>\n \t<li>B<\/li>\n \t<li>Pheromones may not be consciously perceived, and pheromones can have direct physiological and behavioral effects on their recipients.<\/li>\n \t<li>The animal might not be able to recognize the differences in food sources and thus might not be able to discriminate between spoiled food and safe food or between foods that contain necessary nutrients, such as proteins, and foods that do not.<\/li>\n<\/ol>\n<\/div>\n&nbsp;\n\n<\/div>\n<div class=\"cnx-eoc summary\">\n<div class=\"cnx-eoc art-exercise\">\n<div class=\"section empty\">\n<div class=\"section empty\">\n<div class=\"section\">\n<div class=\"body\">\n<div class=\"exercise\">\n<div class=\"title\">\n<div class=\"bcc-box bcc-info\">\n<h3>Exercises<\/h3>\n<div class=\"cnx-eoc multiple-choice\">\n<div class=\"section empty\">\n<div class=\"section\">\n<div class=\"body\">\n<div id=\"m44764-fs-idp207279936\" class=\"exercise\">\n<div class=\"body\">\n<div class=\"problem\">\n\n<span id=\"m44764-fs-idp232916288\"> <\/span><span id=\"m44764-fs-idp119624912\"> 1. <\/span>Which of the following has the fewest taste receptors?\n<div class=\"orderedlist\">\n\nA) fungiform papillae\n\nB) circumvallate papillae\n\nC) foliate papillae\n\nD) filiform papillae\n\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp136791536\" class=\"solution labeled\">\n<div class=\"body\">\n\n<span id=\"m44764-fs-idp17900400\"> Answer: <\/span>D\n\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp12473408\" class=\"exercise\">\n<div class=\"body\">\n<div class=\"problem\">\n\n<span id=\"m44764-fs-idm47740544\"> <\/span><span id=\"m44764-fs-idp52059728\"> 2. <\/span>How many different taste molecules do taste cells each detect?\n<div class=\"orderedlist\">\n\nA) one\n\nB) five\n\nC) ten\n\nD) It depends on the spot on the tongue\n\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idm2197616\" class=\"solution labeled\">\n<div class=\"title\"><span id=\"m44764-fs-idp54308944\">Answer: <\/span>A<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp54312992\" class=\"exercise\">\n<div class=\"body\">\n<div class=\"problem\">\n\n<span id=\"m44764-fs-idp141071216\"> <\/span><span id=\"m44764-fs-idp136286976\"> 3. <\/span>Salty foods activate the taste cells by _____.\n<div class=\"orderedlist\">\n\nA) exciting the taste cell directly\n\nB) causing hydrogen ions to enter the cell\n\nC) causing sodium channels to close\n\nD) binding directly to the receptors\n\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp170039696\" class=\"solution labeled\">\n<div class=\"body\">\n\n<span id=\"m44764-fs-idp93500800\"> Answer: <\/span>A\n\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp166670496\" class=\"exercise\">\n<div class=\"body\">\n<div class=\"problem\">\n\n4. All sensory signals except _____ travel to the _____ in the brain before the cerebral cortex.\n<div class=\"orderedlist\">\n\nA) vision; thalamus\n\nB) olfaction; thalamus\n\nC) vision; cranial nerves\n\nD) olfaction; cranial nerves\n\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp99128144\" class=\"solution labeled\">\n<div class=\"title\"><span id=\"m44764-fs-idp137831200\">Answer: <\/span>B<\/div>\n<div class=\"title\"><\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"body\">\n<div id=\"m44764-fs-idp316672320\" class=\"exercise\">\n<div class=\"body\">\n<div id=\"m44764-fs-idp11174928\" class=\"solution labeled\">\n\n<span id=\"m44764-fs-idp5416736\"> <\/span><span id=\"m44764-fs-idm3550384\"> 5. <\/span>From the perspective of the recipient of the signal, in what ways do pheromones differ from other odorants?\n<div class=\"body\">\n\nPheromones may not be consciously perceived, and pheromones can have direct physiological and behavioral effects on their recipients.\n\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp20836080\" class=\"exercise\">\n<div class=\"title\">\n<div class=\"body\">\n<div class=\"problem\"><span id=\"m44764-fs-idm45895392\"> <\/span><span id=\"m44764-fs-idp111616848\"> 6. <\/span>What might be the effect on an animal of not being able to perceive taste?<\/div>\n<div id=\"m44764-fs-idp138924000\" class=\"solution labeled\">\n<div class=\"title\"><span class=\"epub-only post-text\">\u00a0<\/span><\/div>\n<div class=\"body\">\n\n<span id=\"m44764-fs-idp114669120\"> <\/span>The animal might not be able to recognize the differences in food sources and thus might not be able to discriminate between spoiled food and safe food or between foods that contain necessary nutrients, such as proteins, and foods that do not.\n\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"glossary\" title=\"Glossary\">\n<div class=\"titlepage\">\n<div class=\"bcc-box bcc-success\">\n<h3>Glossary<\/h3>\n<dl>\n \t<dt><strong>bipolar neuron<\/strong><\/dt>\n \t<dd>neuron with two processes from the cell body, typically in opposite directions<\/dd>\n \t<dt><strong>glomerulus<\/strong><\/dt>\n \t<dd>in the olfactory bulb, one of the two neural clusters that receives signals from one type of olfactory receptor<\/dd>\n \t<dt><strong>gustation<\/strong><\/dt>\n \t<dd>sense of taste<\/dd>\n \t<dt><strong>odorant<\/strong><\/dt>\n \t<dd>airborne molecule that stimulates an olfactory receptor<\/dd>\n \t<dt><strong>olfaction<\/strong><\/dt>\n \t<dd>sense of smell<\/dd>\n \t<dt><strong>olfactory epithelium<\/strong><\/dt>\n \t<dd>specialized tissue in the nasal cavity where olfactory receptors are located<\/dd>\n \t<dt><strong>olfactory receptor<\/strong><\/dt>\n \t<dd>dendrite of a specialized neuron<\/dd>\n \t<dt><strong>pheromone<\/strong><\/dt>\n \t<dd>substance released by an animal that can affect the physiology or behavior of other animals<\/dd>\n \t<dt><strong>tastant<\/strong><\/dt>\n \t<dd>food molecule that stimulates gustatory receptors<\/dd>\n \t<dt><strong>umami<\/strong><\/dt>\n \t<dd>one of the five basic tastes, which is described as \u201csavory\u201d and which may be largely the taste of L-glutamate<\/dd>\n<\/dl>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n&nbsp;\n\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>","rendered":"<div class=\"titlepage\">\n<div class=\"abstract\">\n<div class=\"bcc-box bcc-highlight\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to:<\/p>\n<div class=\"itemizedlist\">\n<ul class=\"itemizedlist\">\n<li class=\"listitem\">Explain in what way smell and taste stimuli differ from other sensory stimuli<\/li>\n<li class=\"listitem\">Identify the five primary tastes that can be distinguished by humans<\/li>\n<li class=\"listitem\">Explain in anatomical terms why a dog\u2019s sense of smell is more acute than a human\u2019s<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44764-fs-idp73950336\"> <\/span>Taste, also called <strong><span id=\"m44764-autoid-cnx2dbk-id1839964\"> <\/span>gustation<\/strong>, and smell, also called <span id=\"m44764-autoid-cnx2dbk-id1839968\"> <\/span><strong>olfaction<\/strong>, 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\u2014whether potential mates, predators, or prey\u2014or 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.<\/p>\n<div class=\"section\" title=\"Tastes and Odors\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44764-fs-idp117278560\" style=\"text-align: left;\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Tastes and Odors<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44764-fs-idp155682448\"> <\/span>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 <span id=\"m44764-autoid-cnx2dbk-id1839996\"> <\/span><strong>umami<\/strong> as a fundamental taste occurred fairly recently\u2014it 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.<\/p>\n<p><span id=\"m44764-fs-idp247695328\"> <\/span>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\u2019s perception of flavor is reduced if he or she has congested nasal passages.<\/p>\n<\/div>\n<div class=\"section\" title=\"Reception and Transduction\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h3 id=\"m44764-fs-idp10916192\" style=\"text-align: left;\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Reception and Transduction<\/span><\/span><\/h3>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44764-fs-idp174530608\"> <\/span><span id=\"m44764-autoid-cnx2dbk-id1834540\"> <\/span><strong>Odorants<\/strong> (odor molecules) enter the nose and dissolve in the olfactory epithelium, the mucosa at the back of the nasal cavity (as illustrated in <a class=\"xref target-figure\" title=\"Figure\u00a036.8.\u00a0\" href=\"#attachment_1195\">Figure 17.8<\/a>). The <strong><span id=\"m44764-autoid-cnx2dbk-id1834552\"> <\/span>olfactory epithelium<\/strong> is a collection of specialized olfactory receptors in the back of the nasal cavity that spans an area about 5 cm<sup>2<\/sup> in humans. Recall that sensory cells are neurons. An <strong><span id=\"m44764-autoid-cnx2dbk-id1834560\"> <\/span>olfactory receptor<\/strong>, 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\u2014dogs selectively bred for their sense of smell\u2014have 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.<\/p>\n<p><span id=\"m44764-fs-idp93385696\"> <\/span>Olfactory neurons are <span id=\"m44764-autoid-cnx2dbk-id1827615\"> <\/span><strong>bipolar neurons<\/strong> (neurons with two processes from the cell body). Each neuron has a single dendrite buried in the olfactory epithelium, and extending from this dendrite are 5 to 20 receptor-laden, hair-like cilia that trap odorant molecules. The sensory receptors on the cilia are proteins, and it is the variations in their amino acid chains that make the receptors sensitive to different odorants. Each olfactory sensory neuron has only one type of receptor on its cilia, and the receptors are specialized to detect specific odorants, so the bipolar neurons themselves are specialized. When an odorant binds with a receptor that recognizes it, the sensory neuron associated with the receptor is stimulated. Olfactory stimulation is the only sensory information that directly reaches the cerebral cortex, whereas other sensations are relayed through the thalamus.<\/p>\n<figure id=\"attachment_1195\" aria-describedby=\"caption-attachment-1195\" style=\"width: 400px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_36_03_01.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-4897\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_36_03_01.jpg\" alt=\"Figure_36_03_01\" width=\"400\" height=\"278\" srcset=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_36_03_01.jpg 800w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_36_03_01-300x208.jpg 300w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_36_03_01-768x533.jpg 768w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_36_03_01-65x45.jpg 65w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_36_03_01-225x156.jpg 225w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_36_03_01-350x243.jpg 350w\" sizes=\"auto, (max-width: 400px) 100vw, 400px\" \/><\/a><figcaption id=\"caption-attachment-1195\" class=\"wp-caption-text\">Figure 17.8.\u00a0 In the human olfactory system, (a) bipolar olfactory neurons extend from (b) the olfactory epithelium, where olfactory receptors are located, to the olfactory bulb. (credit: modification of work by Patrick J. Lynch, medical illustrator; C. Carl Jaffe, MD, cardiologist)<\/figcaption><\/figure>\n<div id=\"m44764-fig-ch36_03_01\" class=\"figure\" title=\"Figure\u00a036.8.\u00a0\">\n<div class=\"title\"><\/div>\n<div id=\"m44764-fs-idp59413024\" class=\"note evolution\">\n<div class=\"title\">\n<div class=\"body\">\n<h2 class=\"title\">Pheromones<\/h2>\n<p title=\"Pheromones\">A <span id=\"m44764-autoid-cnx2dbk-id1820576\"> <\/span><strong>pheromone<\/strong> is a chemical released by an animal that affects the behavior or physiology of animals of the same species. Pheromonal signals can have profound effects on animals that inhale them, but pheromones apparently are not consciously perceived in the same way as other odors. There are several different types of pheromones, which are released in urine or as glandular secretions. Certain pheromones are attractants to potential mates, others are repellants to potential competitors of the same sex, and still others play roles in mother-infant attachment. Some pheromones can also influence the timing of puberty, modify reproductive cycles, and even prevent embryonic implantation. While the roles of pheromones in many nonhuman species are important, pheromones have become less important in human behavior over evolutionary time compared to their importance to organisms with more limited behavioral repertoires.<\/p>\n<p><span id=\"m44764-fs-idp259638128\"> <\/span>The vomeronasal organ (VNO, or Jacobson\u2019s organ) is a tubular, fluid-filled, olfactory organ present in many vertebrate animals that sits adjacent to the nasal cavity. It is very sensitive to pheromones and is connected to the nasal cavity by a duct. When molecules dissolve in the mucosa of the nasal cavity, they then enter the VNO where the pheromone molecules among them bind with specialized pheromone receptors. Upon exposure to pheromones from their own species or others, many animals, including cats, may display the flehmen response (shown in <a class=\"xref target-figure\" title=\"Figure\u00a036.9.\u00a0\" href=\"#attachment_1196\">Figure 17.9<\/a>), a curling of the upper lip that helps pheromone molecules enter the VNO.<\/p>\n<p><span id=\"m44764-fs-idp48589024\"> <\/span>Pheromonal signals are sent, not to the main olfactory bulb, but to a different neural structure that projects directly to the amygdala (recall that the amygdala is a brain center important in emotional reactions, such as fear). The pheromonal signal then continues to areas of the hypothalamus that are key to reproductive physiology and behavior. While some scientists assert that the VNO is apparently functionally vestigial in humans, even though there is a similar structure located near human nasal cavities, others are researching it as a possible functional system that may, for example, contribute to synchronization of menstrual cycles in women living in close proximity.<\/p>\n<figure id=\"attachment_1196\" aria-describedby=\"caption-attachment-1196\" style=\"width: 544px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_36_03_02.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-4898\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_02.jpg\" alt=\"Figure\u00a036.9.\u00a0 The flehmen response in this tiger results in the curling of the upper lip and helps airborne pheromone molecules enter the vomeronasal organ. (credit: modification of work by &quot;chadh&quot;\/Flickr)\" width=\"544\" height=\"361\" srcset=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_02.jpg 544w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_02-300x199.jpg 300w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_02-65x43.jpg 65w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_02-225x149.jpg 225w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_02-350x232.jpg 350w\" sizes=\"auto, (max-width: 544px) 100vw, 544px\" \/><\/a><figcaption id=\"caption-attachment-1196\" class=\"wp-caption-text\">Figure 17.9.\u00a0<br \/>The flehmen response in this tiger results in the curling of the upper lip and helps airborne pheromone molecules enter the vomeronasal organ. (credit: modification of work by &#8220;chadh&#8221;\/Flickr)<\/figcaption><\/figure>\n<div id=\"m44764-fig-ch36_03_02\" class=\"figure\" title=\"Figure\u00a036.9.\u00a0\">\n<div class=\"body\">\n<div class=\"mediaobject\"><\/div>\n<\/div>\n<div class=\"title\"><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Taste\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44764-fs-idp3213952\" style=\"text-align: left;\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Taste<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44764-fs-idp10779888\"> <\/span>Detecting a taste (gustation) is fairly similar to detecting an odor (olfaction), given that both taste and smell rely on chemical receptors being stimulated by certain molecules. The primary organ of taste is the taste bud. A <em class=\"glossterm\"><span id=\"m44764-autoid-cnx2dbk-id1828577\"> <\/span>taste bud<\/em> is a cluster of gustatory receptors (taste cells) that are located within the bumps on the tongue called <em class=\"glossterm\"><span id=\"m44764-autoid-cnx2dbk-id1828581\"> <\/span>papillae<\/em> (singular: papilla) (illustrated in <a class=\"xref target-figure\" title=\"Figure\u00a036.10.\u00a0\" href=\"#attachment_1197\">Figure 17.10<\/a>). There are several structurally distinct papillae. Filiform papillae, which are located across the tongue, are tactile, providing friction that helps the tongue move substances, and contain no taste cells. In contrast, fungiform papillae, which are located mainly on the anterior two-thirds of the tongue, each contain one to eight taste buds and also have receptors for pressure and temperature. The large circumvallate papillae contain up to 100 taste buds and form a V near the posterior margin of the tongue.<\/p>\n<figure id=\"attachment_1197\" aria-describedby=\"caption-attachment-1197\" style=\"width: 600px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_36_03_03.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-4899\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_03-1024x375-1.jpg\" alt=\"Figure_36_03_03\" width=\"600\" height=\"220\" srcset=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_03-1024x375-1.jpg 1024w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_03-1024x375-1-300x110.jpg 300w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_03-1024x375-1-768x281.jpg 768w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_03-1024x375-1-65x24.jpg 65w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_03-1024x375-1-225x82.jpg 225w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_03-1024x375-1-350x128.jpg 350w\" sizes=\"auto, (max-width: 600px) 100vw, 600px\" \/><\/a><figcaption id=\"caption-attachment-1197\" class=\"wp-caption-text\">Figure 17.10.\u00a0 (a) Foliate, circumvallate, and fungiform papillae are located on different regions of the tongue. (b) Foliate papillae are prominent protrusions on this light micrograph. (credit a: modification of work by NCI; scale-bar data from Matt Russell)<\/figcaption><\/figure>\n<div id=\"m44764-fig-ch36_03_03\" class=\"figure\" title=\"Figure\u00a036.10.\u00a0\">\n<div class=\"title\"><\/div>\n<p><span id=\"m44764-fs-idp21293008\"> <\/span>In addition to those two types of chemically and mechanically sensitive papillae are foliate papillae\u2014leaf-like papillae located in parallel folds along the edges and toward the back of the tongue, as seen in the Figure<a class=\"xref target-figure\" title=\"Figure\u00a036.10.\u00a0\" href=\"ch36.html#m44764-fig-ch36_03_03\"> 17.10<\/a> micrograph. Foliate papillae contain about 1,300 taste buds within their folds. Finally, there are circumvallate papillae, which are wall-like papillae in the shape of an inverted \u201cV\u201d at the back of the tongue. Each of these papillae is surrounded by a groove and contains about 250 taste buds.<\/p>\n<p><span id=\"m44764-fs-idp99348000\"> <\/span>Each taste bud\u2019s taste cells are replaced every 10 to 14 days. These are elongated cells with hair-like processes called microvilli at the tips that extend into the taste bud pore (illustrate in <a class=\"xref target-figure\" title=\"Figure\u00a036.11.\u00a0\" href=\"#attachment_1198\">Figure 17.11<\/a>). Food molecules (<strong>tastants<\/strong>) are dissolved in saliva, and they bind with and stimulate the receptors on the microvilli. The receptors for tastants are located across the outer portion and front of the tongue, outside of the middle area where the filiform papillae are most prominent.<\/p>\n<figure id=\"attachment_1198\" aria-describedby=\"caption-attachment-1198\" style=\"width: 500px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_36_03_04.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-4900\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_04-1024x842-1.jpg\" alt=\"Figure_36_03_04\" width=\"500\" height=\"411\" srcset=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_04-1024x842-1.jpg 1024w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_04-1024x842-1-300x247.jpg 300w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_04-1024x842-1-768x632.jpg 768w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_04-1024x842-1-65x53.jpg 65w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_04-1024x842-1-225x185.jpg 225w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_36_03_04-1024x842-1-350x288.jpg 350w\" sizes=\"auto, (max-width: 500px) 100vw, 500px\" \/><\/a><figcaption id=\"caption-attachment-1198\" class=\"wp-caption-text\">Figure 17.11.\u00a0 Pores in the tongue allow tastants to enter taste pores in the tongue. (credit: modification of work by Vincenzo Rizzo)<\/figcaption><\/figure>\n<div id=\"m44764-fig-ch36_03_04\" class=\"figure\" title=\"Figure\u00a036.11.\u00a0\">\n<div class=\"title\"><\/div>\n<p><span id=\"m44764-fs-idp69036720\"> <\/span>In humans, there are five primary tastes, and each taste has only one corresponding type of receptor. Thus, like olfaction, each receptor is specific to its stimulus (tastant). Transduction of the five tastes happens through different mechanisms that reflect the molecular composition of the tastant. A salty tastant (containing NaCl) provides the sodium ions (Na<sup>+<\/sup>) that enter the taste neurons and excite them directly. Sour tastants are acids and belong to the thermoreceptor protein family. Binding of an acid or other sour-tasting molecule triggers a change in the ion channel and these increase hydrogen ion (H<sup>+<\/sup>) concentrations in the taste neurons, thus depolarizing them. Sweet, bitter, and umami tastants require a G-protein coupled receptor. These tastants bind to their respective receptors, thereby exciting the specialized neurons associated with them.<\/p>\n<p><span id=\"m44764-fs-idp67938160\"> <\/span>Both tasting abilities and sense of smell change with age. In humans, the senses decline dramatically by age 50 and continue to decline. A child may find a food to be too spicy, whereas an elderly person may find the same food to be bland and unappetizing.<\/p>\n<div id=\"m44764-fs-idp33174096\" class=\"note interactive\">\n<h2 class=\"title\"><span class=\"cnx-gentext-tip-t\">Concept in Action<br \/>\n<\/span><\/h2>\n<div class=\"body\">\n<div class=\"mediaobject\"><span id=\"m44764-fs-idp261625104\"> <\/span><img decoding=\"async\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/taste.png\" alt=\"QR Code representing a URL\" width=\"120\" \/><\/div>\n<p><span id=\"m44764-fs-idp128664496\"> <\/span>View this <a class=\"link\" href=\"http:\/\/openstaxcollege.org\/l\/taste\" target=\"\" rel=\"noopener noreferrer\">animation<\/a> that shows how the sense of taste works.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Smell and Taste in the Brain\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44764-fs-idp19236672\" style=\"text-align: left;\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Smell and Taste in the Brain<\/span><\/span><span id=\"m44764-fs-idp79944432\"><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p>Olfactory neurons project from the olfactory epithelium to the olfactory bulb as thin, unmyelinated axons. The <span id=\"m44764-autoid-cnx2dbk-id1831547\"> <\/span><strong>olfactory bulb<\/strong> is composed of neural clusters called <span id=\"m44764-autoid-cnx2dbk-id1831550\"> <\/span><strong>glomeruli<\/strong>, and each glomerulus receives signals from one type of olfactory receptor, so each glomerulus is specific to one odorant. From glomeruli, olfactory signals travel directly to the olfactory cortex and then to the frontal cortex and the thalamus. Recall that this is a different path from most other sensory information, which is sent directly to the thalamus before ending up in the cortex. Olfactory signals also travel directly to the amygdala, thereafter reaching the hypothalamus, thalamus, and frontal cortex. The last structure that olfactory signals directly travel to is a cortical center in the temporal lobe structure important in spatial, autobiographical, declarative, and episodic memories. Olfaction is finally processed by areas of the brain that deal with memory, emotions, reproduction, and thought.<\/p>\n<p><span id=\"m44764-fs-idp93151360\"> <\/span>Taste neurons project from taste cells in the tongue, esophagus, and palate to the medulla, in the brainstem. From the medulla, taste signals travel to the thalamus and then to the primary gustatory cortex. Information from different regions of the tongue is segregated in the medulla, thalamus, and cortex.<\/p>\n<h2>Summary<\/h2>\n<p>There are five primary tastes in humans: sweet, sour, bitter, salty, and umami. Each taste has its own receptor type that responds only to that taste. Tastants enter the body and are dissolved in saliva. Taste cells are located within taste buds, which are found on three of the four types of papillae in the mouth.<\/p>\n<p><span id=\"m44764-fs-idp132349712\"> <\/span>Regarding olfaction, there are many thousands of odorants, but humans detect only about 10,000. Like taste receptors, olfactory receptors are each responsive to only one odorant. Odorants dissolve in nasal mucosa, where they excite their corresponding olfactory sensory cells. When these cells detect an odorant, they send their signals to the main olfactory bulb and then to other locations in the brain, including the olfactory cortex.<\/p>\n<div class=\"section\" title=\"Higher Processing\">\n<div class=\"note interactive\">\n<div class=\"body\">\n<div class=\"glossary\" title=\"Glossary\">\n<div class=\"titlepage\">\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<ol>\n<li>Which of the following has the fewest taste receptors?\n<ol>\n<li>fungiform papillae<\/li>\n<li>circumvallate papillae<\/li>\n<li>foliate papillae<\/li>\n<li>filiform papillae<\/li>\n<\/ol>\n<\/li>\n<li>How many different taste molecules do taste cells each detect?\n<ol>\n<li>one<\/li>\n<li>five<\/li>\n<li>ten<\/li>\n<li>It depends on the spot on the tongue<\/li>\n<\/ol>\n<\/li>\n<li>Salty foods activate the taste cells by ______.\n<ol>\n<li>exciting the taste cell directly<\/li>\n<li>causing hydrogen ions to enter the cell<\/li>\n<li>causing sodium channels to close<\/li>\n<li>binding directly to the receptors<\/li>\n<\/ol>\n<\/li>\n<li>All sensory signals except _____ travel to the _____ in the brain before the cerebral cortex.\n<ol>\n<li>vision; thalamus<\/li>\n<li>olfaction; thalmus<\/li>\n<li>vision; cranial nerves<\/li>\n<li>olfaction; cranial nerves<\/li>\n<\/ol>\n<\/li>\n<li>From the perspective of the recipient of the signal, in what ways do pheromones differ from other odorants?<\/li>\n<li>What might be the effect on an animal of not being able to perceive taste?<\/li>\n<\/ol>\n<p><strong>Answers<\/strong><\/p>\n<ol>\n<li>D<\/li>\n<li>A<\/li>\n<li>A<\/li>\n<li>B<\/li>\n<li>Pheromones may not be consciously perceived, and pheromones can have direct physiological and behavioral effects on their recipients.<\/li>\n<li>The animal might not be able to recognize the differences in food sources and thus might not be able to discriminate between spoiled food and safe food or between foods that contain necessary nutrients, such as proteins, and foods that do not.<\/li>\n<\/ol>\n<\/div>\n<p>&nbsp;<\/p>\n<\/div>\n<div class=\"cnx-eoc summary\">\n<div class=\"cnx-eoc art-exercise\">\n<div class=\"section empty\">\n<div class=\"section empty\">\n<div class=\"section\">\n<div class=\"body\">\n<div class=\"exercise\">\n<div class=\"title\">\n<div class=\"bcc-box bcc-info\">\n<h3>Exercises<\/h3>\n<div class=\"cnx-eoc multiple-choice\">\n<div class=\"section empty\">\n<div class=\"section\">\n<div class=\"body\">\n<div id=\"m44764-fs-idp207279936\" class=\"exercise\">\n<div class=\"body\">\n<div class=\"problem\">\n<p><span id=\"m44764-fs-idp232916288\"> <\/span><span id=\"m44764-fs-idp119624912\"> 1. <\/span>Which of the following has the fewest taste receptors?<\/p>\n<div class=\"orderedlist\">\n<p>A) fungiform papillae<\/p>\n<p>B) circumvallate papillae<\/p>\n<p>C) foliate papillae<\/p>\n<p>D) filiform papillae<\/p>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp136791536\" class=\"solution labeled\">\n<div class=\"body\">\n<p><span id=\"m44764-fs-idp17900400\"> Answer: <\/span>D<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp12473408\" class=\"exercise\">\n<div class=\"body\">\n<div class=\"problem\">\n<p><span id=\"m44764-fs-idm47740544\"> <\/span><span id=\"m44764-fs-idp52059728\"> 2. <\/span>How many different taste molecules do taste cells each detect?<\/p>\n<div class=\"orderedlist\">\n<p>A) one<\/p>\n<p>B) five<\/p>\n<p>C) ten<\/p>\n<p>D) It depends on the spot on the tongue<\/p>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idm2197616\" class=\"solution labeled\">\n<div class=\"title\"><span id=\"m44764-fs-idp54308944\">Answer: <\/span>A<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp54312992\" class=\"exercise\">\n<div class=\"body\">\n<div class=\"problem\">\n<p><span id=\"m44764-fs-idp141071216\"> <\/span><span id=\"m44764-fs-idp136286976\"> 3. <\/span>Salty foods activate the taste cells by _____.<\/p>\n<div class=\"orderedlist\">\n<p>A) exciting the taste cell directly<\/p>\n<p>B) causing hydrogen ions to enter the cell<\/p>\n<p>C) causing sodium channels to close<\/p>\n<p>D) binding directly to the receptors<\/p>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp170039696\" class=\"solution labeled\">\n<div class=\"body\">\n<p><span id=\"m44764-fs-idp93500800\"> Answer: <\/span>A<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp166670496\" class=\"exercise\">\n<div class=\"body\">\n<div class=\"problem\">\n<p>4. All sensory signals except _____ travel to the _____ in the brain before the cerebral cortex.<\/p>\n<div class=\"orderedlist\">\n<p>A) vision; thalamus<\/p>\n<p>B) olfaction; thalamus<\/p>\n<p>C) vision; cranial nerves<\/p>\n<p>D) olfaction; cranial nerves<\/p>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp99128144\" class=\"solution labeled\">\n<div class=\"title\"><span id=\"m44764-fs-idp137831200\">Answer: <\/span>B<\/div>\n<div class=\"title\"><\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"body\">\n<div id=\"m44764-fs-idp316672320\" class=\"exercise\">\n<div class=\"body\">\n<div id=\"m44764-fs-idp11174928\" class=\"solution labeled\">\n<p><span id=\"m44764-fs-idp5416736\"> <\/span><span id=\"m44764-fs-idm3550384\"> 5. <\/span>From the perspective of the recipient of the signal, in what ways do pheromones differ from other odorants?<\/p>\n<div class=\"body\">\n<p>Pheromones may not be consciously perceived, and pheromones can have direct physiological and behavioral effects on their recipients.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"m44764-fs-idp20836080\" class=\"exercise\">\n<div class=\"title\">\n<div class=\"body\">\n<div class=\"problem\"><span id=\"m44764-fs-idm45895392\"> <\/span><span id=\"m44764-fs-idp111616848\"> 6. <\/span>What might be the effect on an animal of not being able to perceive taste?<\/div>\n<div id=\"m44764-fs-idp138924000\" class=\"solution labeled\">\n<div class=\"title\"><span class=\"epub-only post-text\">\u00a0<\/span><\/div>\n<div class=\"body\">\n<p><span id=\"m44764-fs-idp114669120\"> <\/span>The animal might not be able to recognize the differences in food sources and thus might not be able to discriminate between spoiled food and safe food or between foods that contain necessary nutrients, such as proteins, and foods that do not.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"glossary\" title=\"Glossary\">\n<div class=\"titlepage\">\n<div class=\"bcc-box bcc-success\">\n<h3>Glossary<\/h3>\n<dl>\n<dt><strong>bipolar neuron<\/strong><\/dt>\n<dd>neuron with two processes from the cell body, typically in opposite directions<\/dd>\n<dt><strong>glomerulus<\/strong><\/dt>\n<dd>in the olfactory bulb, one of the two neural clusters that receives signals from one type of olfactory receptor<\/dd>\n<dt><strong>gustation<\/strong><\/dt>\n<dd>sense of taste<\/dd>\n<dt><strong>odorant<\/strong><\/dt>\n<dd>airborne molecule that stimulates an olfactory receptor<\/dd>\n<dt><strong>olfaction<\/strong><\/dt>\n<dd>sense of smell<\/dd>\n<dt><strong>olfactory epithelium<\/strong><\/dt>\n<dd>specialized tissue in the nasal cavity where olfactory receptors are located<\/dd>\n<dt><strong>olfactory receptor<\/strong><\/dt>\n<dd>dendrite of a specialized neuron<\/dd>\n<dt><strong>pheromone<\/strong><\/dt>\n<dd>substance released by an animal that can affect the physiology or behavior of other animals<\/dd>\n<dt><strong>tastant<\/strong><\/dt>\n<dd>food molecule that stimulates gustatory receptors<\/dd>\n<dt><strong>umami<\/strong><\/dt>\n<dd>one of the five basic tastes, which is described as \u201csavory\u201d and which may be largely the taste of L-glutamate<\/dd>\n<\/dl>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"author":90,"menu_order":35,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":"cc-by"},"chapter-type":[],"contributor":[],"license":[57],"class_list":["post-4902","chapter","type-chapter","status-publish","hentry","license-cc-by"],"part":4884,"_links":{"self":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapters\/4902","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/wp\/v2\/users\/90"}],"version-history":[{"count":1,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapters\/4902\/revisions"}],"predecessor-version":[{"id":4903,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapters\/4902\/revisions\/4903"}],"part":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/parts\/4884"}],"metadata":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapters\/4902\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/wp\/v2\/media?parent=4902"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapter-type?post=4902"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/wp\/v2\/contributor?post=4902"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/wp\/v2\/license?post=4902"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}