Gustation and Olfaction The Senses of Taste and Smell Why do we study taste and smell together? SENSORY INTERACTION: the principle that one sense may influence another. The senses of taste and smell have a very cooperative working relationship. Many of the subtle distinctions you may think of as flavors really come from odors Often, if you can’t smell the food, you can’t taste the food. Gustation – The Sense of Taste What is the central muscle involved in taste? Five Distinct Tastes: Five Distinct Tastes: . . . . Umami: the taste of glutamate (MSG) – savory taste in meat and cheese Five Distinct Tastes: Five Distinct Tastes: Each of these tastes developed as survival functions, according to evolutionary psychology. Sweet - energy source Sour – potentially toxic acid Bitter – potential poisons Salty – sodium essential to physiological processes Umami – proteins to grow and repair tissue A Theory Debunked Since 1942, tongue maps like this one were widely published and touted as an accurate portrayal of where certain taste receptors were located. Wine glasses are even designed around this idea. The notion that the tongue is mapped into four areas—sweet, sour, salty and bitter—is wrong. There are five basic tastes identified so far, and the entire tongue can sense all of these tastes more or less equally. The tongue map is easy enough to prove wrong at home. Place salt on the tip of your tongue. You'll taste salt. For reasons unknown, scientists never bothered to dispute this inconvenient truth until 1974, and even today, many textbooks still publish pictures of the tongue map. Remarkably, more is known about vision and hearing, far more complicated senses, than taste. Papillae Those bumps on our tongue are called papillae. Papillae help grip food while your teeth are chewing. They also have another special job They contain your ___________ Each has 200 or more taste buds Individuals vary in their sensitivity to taste sensations, a function of the density of these papillae on the tongue. Taste Buds Each taste bud contains a pore that catches food _____________ Each taste bud pore has 50-100 taste receptor cells with antenna like hairs that sense food molecules 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). Taste Taste receptors reproduce themselves every week or two (this is why it hardly matters if you burn your tongue with hot food). As you grow older, the number of taste buds decreases, as does taste sensitivity. Taste As with other senses, your __________ influence your brain’s response. If you are told something is going to taste bad, your brain responds more negatively. Likewise, being told that a wine costs $90 rather than its real $10 price makes an inexpensive wine taste better and triggers more activity in a brain area that responds to pleasant experiences. As happens with the pain placebo effect, the brain’s thinking frontal lobes offer information that other brain regions act upon. Olfaction Our Sense of Smell How Olfaction Works Smell (Olfaction): operates much like the sense of taste. The physical stimuli are chemical substances carried in the air that are dissolved in fluid, the mucus in the nose. Pathway: Olfactory cilia -> neural impulse -> olfactory nerve -> olfactory bulb (Brain) Olfactory receptors (olfactory cilia) and are located in the upper portion of the nasal passages. The olfactory receptors instantly alert brain through axon fibers the brain. Olfaction is the only sense that is not routed through the __________. This suggests that smell ____________ __________ than the other senses. How Olfaction Works Receptor proteins are embedded on the surface of nasal cavity neurons As a key slips into a lock odor molecules slip into receptors Some odors trigger a combination of receptors Odors are not easily classified. Humans can distinguish among about 10,000 odors, but for some reason have a hard time attaching names to odors quite frequently. 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. Figure 4.51 The olfactory system Pheromones In many animals, the sense of smell is used for communication. For example, insects such as ants and termites and vertebrates such as dogs and cats communicate with each other by secreting and detecting odorous signals called pheromones – especially to signal sexual receptivity, danger, territorial boundaries, and food sources. We humans seem to use the sense of smell primarily in conjunction with taste to seek and sample food, but some evidence exists to suggest that people may also use sexual pheromones as well as pheromones that help us identify family members by smell. For more information: Video on PBS called “Sweaty T-Shirts and Human Mate Choice” for an evolutionary perspective on pheromones Fragrance Effects Research suggests that pleasant scents may trigger pleasant moods and give a boost to workers’ performance. Social psychologist Robert Baron, who has studied these fragrance effects, has patented and is marketing a device that emits pleasant scents. Called PPS (Personal Productivity/Privacy System) it combines fragrance release with a whitenoise generator and an air filter. After testing dozens of smells, Baron found that lemon and light floral had broad appeal (pine was the least popular odor), and is marketing discs producing these odors with the PPS. On a much larger scale, Shimizu Corporation has also patented an “odordelivery” for commercial buildings. For example, it pumps a citrus odor through an office building’s ventilation ducts every two minutes. “The fragrance sense can be fundamental to controlling conditions for office workers,” says Junichi Yagi, a representative for Shimizu. He cites a monthlong study of Japanese keypunchers in which those who inhaled a lemon aroma make 54 percent fewer errors than those who sniffed plain air. While the citrus odor seemed to make people more alert, other smells, such as spiced apple, seemed to aid relaxation.