Chemical Senses

10 Key excerpts on "Chemical Senses"

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  Sensation, Perception and Action

  An Evolutionary Perspective

  • Johannes Zanker(Author)
  • 2010(Publication Date)
  • Bloomsbury Academic

    (Publisher)

  112 1 OVERVIEW For Chemical Senses, the physical, or better chemical, properties of sensory stimuli are the starting point to ask the same questions that we used to understand the relevance of other sensory modalities: What is the medium carrying the stimulus? How can it be detected? What are the limiting factors of detecting, discriminating and recognising stimuli? Are there any parallels to technical applications? The sense of smell is discussed in view of the sensor that is tasked with picking up chemicals from the air, which leads to an inherently narrow receptor tuning, and as a result of this to difficulties for a perceptual classification system for odours. The olfactory population code is explained as a highly evolved strategy to combine information from narrowly tuned receptors, allowing for the classification of a huge range of complex odours. Odour localisation is discussed as a typical example of active exploration, through sniffing. The sense of taste is discussed along the same line of thought – the basic sensor function, which again hinges on chemical binding of mol-ecules, but now retrieving taste stimuli from a liquid medium; basic taste qualities; the dimensionality of this sensory space. The similarities and differences of the two Chemical Senses lead us to consider some aspects of smell–taste associations that are involved in the complex sensation of flavour. The experience of spicy food highlights a peculiar cross-talk between sensory channels, which gives the label ‘hot’ a new meaning. The predomi-nance of olfactory and gustatory object-related recognition and classification is at the starting point of questioning the nature of perceptual experience in the chemical sensory domain, trying to assess the evolutionary benefit of opening up these sensory channels for humans.

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  Nutrient Metabolism

  Structures, Functions, and Genes

  • Martin Kohlmeier(Author)
  • 2015(Publication Date)
  • Academic Press

    (Publisher)

  Chapter 1

  Chemical Senses

  Chemical Senses are essential to preserving the human existence. The ability to detect odors from foods is an important appetite stimulant and often initiates the secretion of digestive juices. Aversive reactions to foul odors provide some protection against ingestion of unsafe foods. In this chapter, the anatomical structure, molecular mechanisms, and variation in olfaction (smell) are described and explained. The ability of healthy people to distinguish a wide range of tastes (gustation) is also explained in detail, describing taste buds, innervation, taste-enhancing secretions, the molecular basis of taste signaling, salty taste, sweet taste, bitter taste, sour taste, meaty taste (umami), savory taste (kokumi), fat taste, calcium taste, other taste qualities, and variation in taste sensitivity. Intestinal sensing and chemesthesis also play a role in digestion, and this is explained in this chapter.

  Keywords

  Smell; Chemical Senses; olfactory nerve; odors; olfaction; smell; taste buds; innervation; taste-enhancing secretions; the molecular basis of taste signaling; salty taste; sweet taste; bitter taste; sour taste; meaty taste (umami); kokumi; fat taste; calcium taste; mechanoreceptors; nociceptors; intestinal sensing; chemesthesis; digestion

  Chapter Outline

  Smell  1

  Taste  4

  Intestinal Sensing  16

  Physical Sensing and Chemesthesis  20

  Smell

  The ability to detect odors from foods is an important appetite stimulant and often initiates the secretion of digestive juices. Aversive reactions to foul or otherwise disagreeable odors provide some protection against ingestion of unsafe foods. Impaired ability to smell, which becomes more common with advancing age, increases the risk of inadequate food intake and food poisoning.

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  Chemometrics

  Chemical and Sensory Data

  • David R. Burgard(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 5 The Chemical Senses

  I. Introduction

  This chapter reviews the functional anatomy and perceptual processes of the Chemical Senses: taste, smell, and the common chemical sense. While it is possible to collect sensory data without this knowledge, interpretation of that data is not. In sensory evaluation studies, the human subject is often viewed as an instrument which is used to determine some property of the product samples being studied. Since the product is of primary interest, it is often easy to overlook the properties of the instrument. It is those properties, however, which determine the type and quality of data that is obtained. As an analogy, consider a liquid chromatograph. This instrument can be used to determine the concentrations of specific chemicals in a sample, the relative amounts of several chemicals in the sample, or even the total number of different chemicals present. The type and quality of data obtained depends on several variables. These include the way the samples are prepared for injection into the instrument, the solvent used to extract the samples and in which they are dissolved, the material in the column, the pressure at which the samples are pumped through the column, etc. A change in any one or combination of these variables will affect the data obtained in measurable ways. In a similar fashion, the human instrument possesses properties, which are not determined by the investigator but are brought to the situation, that affect the data obtained in a sensory evaluation study. These properties, not all of which are clearly understood, are determined by functional operating characteristics of the sensory systems. The analogy between a human sensory instrument and a liquid chromatograph cannot be carried too far, however, because unlike the passive chromatograph the human instrument is an active instrument. The information fed into the human instrument is actively processed such that the output of the instrument does not always, or even usually, stand in one-to-one relationship with the input. This processing begins at the earliest stages of the perceptual process, interaction of sample with sensory receptors, and continues through the last stages of the process in which the subject makes some sort of judgment about the sample (e.g., quality, intensity, or hedonic tone of the sample). The sensory properties of the human instrument are also affected by higher-order properties called cognitive processes which affect the data and, perhaps of greatest importance, the ability of the subject to provide the data of interest. To properly interpret output from a sensory system, some knowledge of that system is absolutely necessary. Fortunately, the study of sensory processes is a very active area and several excellent texts and handbooks are available.1 , 2 , 3 , 4 , 5 , 6 , 7 and 8

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  Principles of Anatomy and Physiology for Nursing and Healthcare Students in Australia, 1st Edition

  • Ian Peate, Suzanne Evans, Amy Byrne, Will Deasy, Michele Dowlman, Pauline Gillan, Siva Purushothuman, Dan Wadsworth(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  Sensory systems in the human body differ vastly in complexity. The chapter on the nervous system described how a sensory input (stimulus) is gathered and delivered to the central nervous system via a sensory receptor. The receptor is a transducer that converts the stimulus into an intracellular signal by evoking a change in membrane potential. If the stimulus is above the threshold value, action potentials are generated and pass along the afferent neurone to the central nervous system. In the special senses, the sensory receptors detecting the stimuli are highly sophisticated in multicellular sense organs like the ear and the eye, which are made up of non-neural receptor cells (i.e. ear hair cells, eye photoreceptors and tastebuds). These cells synapse and release neurotransmitters directly on to sensory neurons initiating action potentials. In all these sections there will be a review of the anatomy of the particular organs involved in these senses, followed by a discussion of the physiology of how these senses are monitored and create action potentials to be transmitted to the brain. Finally, the pathways these action potentials take to the brain will be reviewed, along with a brief discussion of the processing of this information in the brain itself. 15.1 The Chemical Senses LEARNING OBJECTIVE 15.1 Describe the process by which we perceive smell. With regard to the senses, the Chemical Senses are the senses of smell and taste, which rely on chemoreceptors. There are two main types of chemoreceptor: • distance chemoreceptors — for instance, the olfactory (smell) receptors • direct chemoreceptors — for instance, the sense of taste, which relies on the tastebuds. The sense of smell (olfaction) In evolutionary terms, the sense of smell is one of the oldest senses, and the most primitive vertebrate brains have well-developed regions for processing olfactory information.

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  Physiological Psychology

  • Thomas Brown(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  Following the trail toward higher concentrations of the odor, he may, if he is lucky, come upon a receptive female moth who will find him attrac-tive enough to mate with him. Then he will die. You may think of your Chemical Senses as nice to have and occa-sionally useful—especially during a French food repast when the tastes and aromas of the crepes suzettes create an extraordinary expe-rience. But to our hapless moth, an acute sense of smell is the only thing between dying childless and leaving his genes to populate the world in the next generation. And insects are not the only creatures which rely heavily on their Chemical Senses—the mammals, and the rodents in particular, use these senses to find food and avoid poisons, to elude predators, to mate, to fight, and generally to survive. Human beings may not get any tax breaks if they lose their sense of smell or taste, and these losses may not be so devastating as the loss of sight or hearing. But the Chemical Senses are extremely important to the lower animals, and some scientists hypothesize that they may be more important to humans than most of us realize. The industries which concentrate on perfumes, deodorants, and food flavorings are certainly not going broke. In this chapter we will first discuss the stimulus for the Chemical Senses, then we will go on to consider the sense of taste, and finally the olfactory system. the chetnicßl StltnuluS The study of the Chemical Senses has lagged behind the study of vision and audition, partly because taste and olfaction are considered less important to human beings. The Chemical Senses have also been much more difficult to study because it is very difficult to identify the stimulus. identifying the stimulus m t n e Chemical Senses, the intensity of the stimulus represents the concentration of molecules which are presented to the receptor cells in the nose or on the tongue. The experimenter can specify the number 148 physiological psychology

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  Introduction to Psychological Science

  Integrating Behavioral, Neuroscience and Evolutionary Perspectives

  • William J. Ray(Author)
  • 2021(Publication Date)
  • Routledge

    (Publisher)

  taste are different from vision and hearing. Rather than photons or pressure, we experience the chemicals in our world with smell and taste. We notice the smell of good food cooking, and we are attracted to where the smell is coming from. As this is happening, our digestive system prepares to process the food we are about to eat. However, if we open a container with rotten food, that is a different story. We are repulsed just by a quick experience of the odor.

  Olfaction refers to your sense of smell. In your nose are sensory neurons that are responsive to chemicals that we experience as odors. These receptors produce electrical signals and send a pattern of activity to the olfactory bulb, which processes the signal and serves as a relay station to other areas of the brain including the limbic area. Your physiological state can determine what and how you experience smells. We have a long evolutionary history of protecting ourselves through the smells and tastes that we experience. It is estimated that we may be able to distinguish more than 10,000 different chemical smells.

  Taste refers to the five qualities processed by our gustatory system: (1) sweet, (2) bitter, (3) salty, (4) sour, and (5) umami. Flavor, which is more complex, refers to the combination of sensory processes that we experience in terms of taste, smell, and texture as well as our experience of chewing. Taste signals are produced in the mouth—most of our taste buds are located on the tongue—and go through the brain stem and the thalamus to the area of the brain related to taste.

  Learning Objective 5: Describe the different senses of touch and what happens when we experience pain.

  Touch plays a critical role in our lives. Historically, a distinction has been made between active and passive touch: (1) active touch is when you move your body, generally your hands, against another object or person; and (2) passive touch is when another person or object rubs against your skin. Both use the same receptors in the skin and the same pathways to the brain; however, there are differences: (1) the cognitive features may differ; (2) there is a close connection between active touch and the motor system; and (3) active and passive touch show different patterns of brain activation. Your hand has four types of receptors that supply information to your brain: (1) Meissner corpuscles, (2) Merkel cells, (3) Pacinian corpuscles, and (4) Ruffini endings. The four types of receptors work together to give you a sense of shape, texture, movement, and pressure; they do this by being sensitive to skin stretch, edges, lateral motion, and vibration. The information from the touch receptors goes through the spinal cord and then to the brain stem, the thalamus, and the somatosensory cortex in the parietal lobe. Touch information on the somatosensory cortex is organized in terms of locations on the body. The motor cortex is organized similarly to the sensory cortex, allowing for an integration of the experience of touch with making actions.

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  Sensation and Perception

  • E. Goldstein, James Brockmole(Authors)
  • 2016(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  CHAPTER CONTENTS Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 362 CHAPTER 15 The Chemical Senses Because the receptors that serve taste and smell are con- stantly exposed not only to the chemicals they are designed to sense but also to harmful materials such as bacteria and dirt, they undergo a cycle of birth, development, and death over 5–7 weeks for olfactory receptors and 1–2 weeks for taste receptors. This constant renewal of the receptors, called neurogenesis, is unique to these senses. In vision and hearing, the receptors are safely protected inside structures such as the eye and the inner ear, and in the cutaneous senses, under the skin; however, the receptors for taste and smell are relatively unprotected and therefore need to be constantly renewed. In this chapter, we will consider taste first and then olfac- tion. We will describe the psychophysics and anatomy of each system and then how different taste and smell qualities are coded in the nervous system. Finally, we consider flavor, which results from the interaction of taste and smell. Taste Everyone is familiar with taste. We experience it every time we eat. (Although later in the chapter we will see that what we ex- perience when we eat is actually “flavor,” which is a combina- tion of taste and olfaction.) Taste occurs when molecules enter the mouth in solid or liquid form and stimulate taste receptors on the tongue. The perceptions resulting from this stimula- tion have been described in terms of five basic taste qualities.

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  The Lexical Field of Taste

  A Semantic Study of Japanese Taste Terms

  • A. E. Backhouse(Author)
  • 1994(Publication Date)
  • Cambridge University Press

    (Publisher)

  The taste cells are stimulated by sapid (i.e. taste-bearing) substances when in solution or when dissolved in the saliva. Since the cells are sensitive to chemical energy, they are known as chemoreceptors, and the senses of taste and smell (whose chemoreceptors are the cells of the olfactory epithelium) are together referred to as the Chemical Senses. Scientifically, the study of taste is thus normally restricted to the study of various forms of sensitivity and perception arising from the stimulation of the taste cells by sapid substances in solution. 2 Taste and taste terms Compared with the senses of vision and hearing, the workings of the Chemical Senses are poorly understood. Work on taste has generally assumed that there are four primary tastes in man, namely sweet, sour, salty and bitter, and that these are detected by taste buds in different areas of the tongue and mouth. Scientific discussion continues to be conducted in terms of these four qualities (ostensively defined in terms of the chemical substances sucrose, tartaric acid, sodium chloride and quinine, respectively), but their status has frequently been called into question: The range of qualities is subdivided for convenience into the four common tastes, Sweet, Sour, Salt and Bitter...(They) are referred to here deliberately as the common tastes so as to avoid any assumption that they are genuine primaries. There is relatively little evidence to support the concept of primary tastes. Whereas attempts have been made to synthesize more complex tastes in terms of these four qualities, there are certain tastes, such as Metallic, which cannot be synthesized in this way.

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  Psychology Around Us

  • Ronald Comer, Nancy Ogden, Michael Boyes, Elizabeth Gould(Authors)
  • 2017(Publication Date)
  • Wiley

    (Publisher)

  gustatory sense , emerged early in our evolutionary history (Doty, 2015). The sense of smell, in particular, is more sensitive and of greater significance to less complex animals, who use it for social communication as well as finding food and avoiding predators (Breslin, 2013; Stevens, 2013). This is less so for humans who rely more heavily on vision (Valentin, 2015). However, the contributions of both smell and taste to the safety, social communication, and overall quality of life in humans are often underestimated. The ability to detect dangerous odours, such as smoke or a gas leak, or dangerous flavours, such as tainted food or poison, can be critical to our survival. In addition, some of our greatest pleasures in life come from the ability to smell and taste—to smell a rose or, as we all know, to enjoy a good meal.

  In this section, we will explore the environmental stimuli that create aromas and flavours, the organs we use to sense those stimuli, and how we transform environmental stimuli into brain signals that eventually help us perceive different smells and tastes. We will also discuss the development of these abilities, some very interesting differences among people in their ability to taste and smell things, and some problems that can occur in the olfactory and gustatory systems.

  Smell and Taste: How They Work

  Smells Around Us

  Sensation in the smell or olfactory system begins when chemicals called odorants enter the nose, as shown later in the chapter in the feature “Tying it Together 5.1 : Your Brain and Behaviour.” Odorants are converted to neural signals at sensory receptors located in our nasal mucosa. These sensory receptors are located on the cilia, or hairlike structures, of olfactory receptor neurons (Scott, McBride, & Schneider, 2016).

  When odorants enter the nose, these chemicals bind to specific receptors located on the olfactory receptor neurons in a lock-and-key fashion. Only certain airborne chemicals bind to specific receptors (Doty, 2015). When enough odorant molecules have bound to receptors, the combination sets off an action potential in the olfactory receptor neuron. As we described in Chapter 3 , the action potential or firing

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  Introduction to the Senses

  From Biology to Computer Science

  • Terry R. J. Bossomaier(Author)
  • 2012(Publication Date)
  • Cambridge University Press

    (Publisher)

  The intensity variations to which humans seem to be sensitive are about 2 × 10 5 across multiple receptors, giving about 36 bits (Dusenbury, 1992). The number of smell components we can manipulate is very hard to quantify. At the simplest level we would say that it was somewhat equivalent to the approximate primary odours, say 20. This would give us 100 bits of information per sniff. This is far too low. A better estimate for a basis might be to use the number of receptor proteins coded for in the genes. An upper estimate would be around 1000, giving us about 5000 bits per sniff. This corresponds to roughly 1 bit per neuron which is much lower than we get in other modalities. However, such a space would be extremely sparsely occupied, thus this does not seem a useful viewpoint. Whatever way we look at it, olfaction is a low bandwidth sense (Laurent, 1999). 9.5 Taste The tongue in addition to holding the taste buds has many cells which are touch sensitive. The tongue is like a super-sensitive somatosensory organ. It has highly developed tactile and chemical sensors. The texture, the surface properties, of things we put into our mouths is also important to monitoring what we eat. There are four or five categories of taste: salty; sweet; bitter; sour; and unami. The latter, a sensitivity to glutamate (occurring, for example, as the flavour enhancer monosodium glutamate or MSG), is still somewhat controversial. Taste has an immediate survival value. Both bitter and sweet, at least, appear innate. Bitter is indicative of alkaloids, chemicals plants specifically manufacture to deter being eaten. Some of the most poisonous naturally occurring chemicals are alkaloids, such as the berries of yew trees and the deadly aconitine from monkshood, Britain’s most toxic plant. We seem to find fat an essential component of desirable food, from salad dressings, butter in sandwiches to the rich realm of French sauces.

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