Gustation and OlfactionGustation and OlfactionThe Senses of Taste and SmellThe Senses of Taste and Smell

Why do we study taste and smell Why do we study taste and smell together?together?

SENSORY INTERACTIONSENSORY INTERACTION: the principle that one : the principle that one sense may influence another.sense may influence another.

The senses of taste and smell have a very The senses of taste and smell have a very cooperative working relationship. cooperative working relationship.

Many of the subtle distinctions you may Many of the subtle distinctions you may think of as flavors really come from odors think of as flavors really come from odors

Often, if you can’t smell the food, you can’t Often, if you can’t smell the food, you can’t taste the food.taste the food.

Gustation – The Sense of TasteGustation – The Sense of Taste

What is the central muscle involved in What is the central muscle involved in taste? taste?

Five Distinct Tastes:Five Distinct Tastes:

Five Distinct Tastes:Five Distinct Tastes: .. .. .. .. Umami: the taste of glutamate (MSG) – savory taste Umami: the taste of glutamate (MSG) – savory taste

in meat and cheesein meat and cheese

Five Distinct Tastes:Five Distinct Tastes:Five Distinct TastesFive Distinct Tastes:: Each of these tastes developed as survival Each of these tastes developed as survival

functions, according to functions, according to evolutionary evolutionary psychologypsychology..

Sweet - energy sourceSweet - energy sourceSour – potentially toxic acidSour – potentially toxic acidBitter – potential poisonsBitter – potential poisonsSalty – sodium essential to physiological Salty – sodium essential to physiological processesprocessesUmami – proteins to grow and repair tissueUmami – proteins to grow and repair tissue

A Theory DebunkedA Theory DebunkedSince 1942, tongue maps like this one were Since 1942, tongue maps like this one were widely published and touted as an accurate widely published and touted as an accurate portrayal of where certain taste receptors portrayal of where certain taste receptors were located. were located.

Wine glasses are even designed around this idea.Wine glasses are even designed around this idea.

The notion that the tongue is mapped into The notion that the tongue is mapped into four areas—sweet, sour, salty and bitter—is four areas—sweet, sour, salty and bitter—is wrong.  wrong.  There are five basic tastes There are five basic tastes identified so far, and the entire tongue identified so far, and the entire tongue can sense all of these tastes more or less can sense all of these tastes more or less equally.equally.The tongue map is easy enough to prove The tongue map is easy enough to prove wrong at home.  wrong at home. 

Place salt on the tip of your tongue.  You'll Place salt on the tip of your tongue.  You'll taste salt.  taste salt. 

For reasons unknown, scientists never For reasons unknown, scientists never bothered to dispute this inconvenient bothered to dispute this inconvenient truth until 1974, and even today, many truth until 1974, and even today, many textbooks still publish pictures of the textbooks still publish pictures of the tongue map.tongue map.

Remarkably, more is known about vision Remarkably, more is known about vision and hearing, far more complicated senses, and hearing, far more complicated senses, than taste. than taste. 

PapillaePapillaeThose bumps on our tongue Those bumps on our tongue are called are called papillaepapillae..

Papillae help grip food while Papillae help grip food while your teeth are chewing. They your teeth are chewing. They also have another special jobalso have another special job

They contain your They contain your ______________________

Each has 200 or more taste Each has 200 or more taste budsbuds

Individuals vary in their Individuals vary in their sensitivity to taste sensations, sensitivity to taste sensations, a function of the density of a function of the density of these papillae on the tongue.these papillae on the tongue.

Taste BudsTaste Buds

Each taste bud contains a pore Each taste bud contains a pore that catches food _____________that catches food _____________Each taste bud pore has 50-100 Each taste bud pore has 50-100 taste receptor cells with antenna taste receptor cells with antenna like hairs that sense food like hairs that sense food moleculesmolecules

Figure 4.49: The tongue and taste. (a) Taste buds line the trenches around tiny bumps on the tongue called papillae. There are three types of papillae, which are distributed on the tongue as shown in (b). The taste buds found in each type of papillae show slightly different sensitivities to the four basic tastes, as mapped out in the graph at the top. Thus, sensitivity to the primary tastes varies across the tongue, but these variations are small, and all four primary tastes can be detected wherever there are taste receptors. (Data adapted from Bartoshuck 1993a).

TasteTasteTaste receptors reproduce themselves every week or Taste receptors reproduce themselves every week or two (this is why it hardly matters if you burn your tongue two (this is why it hardly matters if you burn your tongue with hot food).with hot food).As you grow older, the number of taste buds decreases, As you grow older, the number of taste buds decreases, as does taste sensitivity.as does taste sensitivity.

TasteTasteAs with other senses, your __________ As with other senses, your __________ influence your brain’s response. influence your brain’s response. If you are told something is going to taste bad, your If you are told something is going to taste bad, your

brain responds more negatively.brain responds more negatively. Likewise, being told that a wine costs $90 rather than Likewise, being told that a wine costs $90 rather than

its real $10 price makes an inexpensive wine taste its real $10 price makes an inexpensive wine taste better and triggers more activity in a brain area that better and triggers more activity in a brain area that responds to pleasant experiences.responds to pleasant experiences.

As happens with the pain placebo effect, the As happens with the pain placebo effect, the brain’s thinking frontal lobes offer information brain’s thinking frontal lobes offer information that other brain regions act upon.that other brain regions act upon.

OlfactionOlfactionOur Sense of SmellOur Sense of Smell

How Olfaction WorksHow Olfaction WorksSmell (Olfaction): Smell (Olfaction): operates much like the sense operates much like the sense of taste.of taste. The physical stimuli are The physical stimuli are chemical substances chemical substances carried carried

in the air that are dissolved in fluid, the mucus in the in the air that are dissolved in fluid, the mucus in the nose. nose.

Pathway: Pathway: Olfactory cilia -> neural impulse -> olfactory Olfactory cilia -> neural impulse -> olfactory nerve -> olfactory bulb (Brain)nerve -> olfactory bulb (Brain)

Olfactory receptors (olfactory cilia) and are located in the upper Olfactory receptors (olfactory cilia) and are located in the upper portion of the nasal passages. portion of the nasal passages.

The olfactory receptors The olfactory receptors instantlyinstantly alert brain through axon fibers alert brain through axon fibers the brain. the brain.

Olfaction is the only sense that is not routed through the Olfaction is the only sense that is not routed through the __________. __________. This suggests that smell ____________ __________ than the This suggests that smell ____________ __________ than the other senses.other senses.

How Olfaction WorksHow Olfaction WorksReceptor proteins are embedded on the surface Receptor proteins are embedded on the surface of nasal cavity neuronsof nasal cavity neurons As a key slips into a lock As a key slips into a lock odor molecules slip odor molecules slip

into receptorsinto receptors Some odors trigger a combination of receptors Some odors trigger a combination of receptors

Odors are not easily classified. Odors are not easily classified. Humans can distinguish among about 10,000 odors, Humans can distinguish among about 10,000 odors,

but for some reason have a hard time attaching but for some reason have a hard time attaching names to odors quite frequently.names to odors quite frequently.

Figure 4.51 The olfactory system

Figure 4.51: The olfactory system. Odor molecules travel through the nasal passages and stimulate olfactory cilia. An enlargement of these hairlike olfactory receptors is shown in the inset. The olfactory nerves transmit neural impulses through the olfactory bulb to the brain.

PheromonesPheromonesIn many animals, the sense of smell is used for In many animals, the sense of smell is used for communication. For example, insects such as ants and communication. For example, insects such as ants and termites and vertebrates such as dogs and cats termites and vertebrates such as dogs and cats communicate with each other by secreting and detecting communicate with each other by secreting and detecting odorous signals called odorous signals called pheromonespheromones – especially to signal – especially to signal sexual receptivity, danger, territorial boundaries, and food sexual receptivity, danger, territorial boundaries, and food sources. sources. We humans seem to use the sense of smell primarily in We humans seem to use the sense of smell primarily in conjunction with taste to seek and sample food, but some conjunction with taste to seek and sample food, but some evidence exists to suggest that people may also use sexual evidence exists to suggest that people may also use sexual pheromones as well as pheromones that help us identify pheromones as well as pheromones that help us identify family members by smell.family members by smell.For more information:For more information:

Video on PBS called “Sweaty T-Shirts and Human Mate Video on PBS called “Sweaty T-Shirts and Human Mate Choice” for an evolutionary perspective on pheromonesChoice” for an evolutionary perspective on pheromones

Fragrance EffectsFragrance EffectsResearch suggests that pleasant scents may trigger pleasant moods Research suggests that pleasant scents may trigger pleasant moods and give a boost to workers’ performance. and give a boost to workers’ performance. Social psychologist Robert Baron, who has studied these fragrance Social psychologist Robert Baron, who has studied these fragrance effects, has patented and is marketing a device that emits pleasant effects, has patented and is marketing a device that emits pleasant scents. Called PPS (Personal Productivity/Privacy System) it scents. Called PPS (Personal Productivity/Privacy System) it combines fragrance release with a white noise generator and an air combines fragrance release with a white noise generator and an air filter. filter. After testing dozens of smells, Baron found that lemon and light floral After testing dozens of smells, Baron found that lemon and light floral had broad appeal (pine was the least popular odor), and is marketing had broad appeal (pine was the least popular odor), and is marketing discs producing these odors with the PPS. discs producing these odors with the PPS. On a much larger scale, Shimizu Corporation has also patented an On a much larger scale, Shimizu Corporation has also patented an “odor delivery” for commercial buildings. For example, it pumps a “odor delivery” for commercial buildings. For example, it pumps a citrus odor through an office building’s ventilation ducts every two citrus odor through an office building’s ventilation ducts every two minutes. “The fragrance sense can be fundamental to controlling minutes. “The fragrance sense can be fundamental to controlling conditions for office workers,” says Junichi Yagi, a representative for conditions for office workers,” says Junichi Yagi, a representative for Shimizu. He cites a month long study of Japanese keypunchers in Shimizu. He cites a month long study of Japanese keypunchers in which those who inhaled a lemon aroma make 54 percent fewer which those who inhaled a lemon aroma make 54 percent fewer errors than those who sniffed plain air. While the citrus odor seemed errors than those who sniffed plain air. While the citrus odor seemed to make people more alert, other smells, such as spiced apple, to make people more alert, other smells, such as spiced apple, seemed to aid relaxation. seemed to aid relaxation.