Olfaction sense

It is believed that this close link between the olfactive sense and the limbic region is the reason for such a close association between smell and emotion. To try to understand this link, researchers have studied... 

Because of the relative ease of measurement of many of nitrobenzene s properties and its ready detectability by both chemical analysis and human olfaction (sense of smell), its release, transport and fate, and the consequent exposure of human beings have been studied over a considerable period of time. Thus, the potential for human exposure to nitrobenzene is better understood than that of many other chemicals. 

It has to be remarked that in spite of the widely accepted term electronic nose, current devices are still far from the structure and functions of natural olfaction sense. The unique common feature between artificial and natural system is that both are largely based on arrays of nonselective sensors. The concept underlying electronic nose systems has been demonstrated to be independent on the particular sensor mechanism indeed during the last two decades almost all the available sensor technologies have been utilized as electronic noses. Clearly, all these sensors are very different from the natural receptors. These dissimilarities make the perception of electronic nose very different from that of natural olfaction, so that the instrumental perception of the composition of air cannot be called odor measurement because odor is the sensation of smell as perceived by human olfaction. Nonetheless, the term odor analysis with electronic noses is now largely adopted, but it is important to keep in mind, especially in medical applications, that the electronic nose measurement may be very distant from the human perception. 

In 1986, the National Geographic Society, in cooperation with the MoneU Center, conducted a worldwide survey of the sense of smell. Over 10 million survey forms were sent to readers of the Society s journal, of which close to 1.5 million forms were completed and returned. With responses to 40 demographic and 42 odor-related questions, the results constitute the largest set of data on human olfaction (4). 

There are certain weU-estabUshed facts about olfaction (6). AU normal people can smell. People suffering from brain lesions, injured olfactory nerve, or obstmcted nasal passages may be anosmic. Cases of preferential anosmia, ie, abUity to sense certain smells and not others, are not weU estabUshed. Such cases occur, but Utde is known of them. 

Odor travels downwind. Many animals have a keener sense of olfaction than humans. Insects have such extraordinary keenness of smell that it may be a different modaUty of the chemical sense from that known to humans. 

Odors play a much greater role in human behavior than previously thought. The sense of smell provides a direct link with the function of the brain therefore, the further study of olfaction can only advance the learning of causes and effects of stimuli to the brain. 

The oscillation of membrane current or membrane potential is well-known to occur in biomembranes of neurons and heart cells, and a great number of experimental and theoretical studies on oscillations in biomembranes as well as artificial membranes [1,2] have been carried out from the viewpoint of their biological importance. The oscillation in the membrane system is also related to the sensing and signal transmission of taste and olfaction. Artificial oscillation systems with high sensitivity and selectivity have been pursued in order to develop new sensors [3-8]. 

Parsons T. (1971). Anatomy of nasal structures from a comparative viewpoint. In Handbook of Sensory Physiology Chemical Senses, Pt. 1 Olfaction (Beidler L.M., ed.). Springer, Berlin, Vol. 4, pp. 1-26. 

Multiple senses, including taste, contribute to our total perception of food. Our perception of the flavor of food is a complex experience based upon multiple senses taste per se, which includes sweet, sour, salty and bitter olfaction, which includes aromas touch, also termed mouth feel , that is, texture and fat content and thermoreception and nociception caused by pungent spices and irritants. Taste proper is commonly divided into four categories of primary stimuli sweet, sour, salty and bitter. One other primary taste quality, termed umami (the taste of L-glutamate), is still somewhat controversial. Mixtures of these primaries can mimic the tastes of more complex foods. 

Olfaction, once thought to be a primitive sense, is now recognized as an elaborate sensory system that deploys a large family of odorant receptors to analyse the chemical environment. Interactions between these receptors and their diverse natural binding molecules (ligands) translate the world of odors into a neural code. Humans have about 350 odorant receptors. Rodents have more than a thousand. 

The sense of smell in humans is not limited to detection of those volatile molecules inhaled through the nose, termed orthonasal olfaction. Molecules released at the back of the mouth, particularly in the chewing of food, can make their way up through the nasopharynx to the olfactory epithelium, termed retronasal olfaction. This system is activated when air is exhaled. Orthonasal olfaction is used to detect the scent of flowers and perfumes, food aromas, the presence of skunks, and the like. Retronasal olfaction detects the volatile molecules released from food. It is retronasal olfaction that makes a major olfactory contribution to the taste of food. And it is retronasal olfaction that helped to elicit Proust s profound reaction to a madeleine dipped in tea. 

Beyond that, the sense of olfaction does not depend on the concentration of the odorant concentration invariance. If you are exposed to jasmine at very low concentration, it smells like jasmine if the concentration is significantly raised, it still smells like jasmine. Perhaps more to the point is the concentration invariance of complex aromas such as that of coffee. The brain forms a single perception from complex inputs, regardless of the intensity of the signal. Olfaction has this property in common with taste. 

Here is a bit of a complication there is a lot of individual variation in the sense of human olfaction. Not everything smells the same to everyone. This holds both for the intensity of the perceived smeU as well as for its quality pleasant, floral, skunky, sweaty, or no odor at all. Andreas Keller has recently demonstrated that some significant part of this individual variation in the sense of smell derives from genetic variation in human odorant genes. Specifically, two single nucleotide polymorphisms (SNPs), leading to two amino acid substitutions in an odorant receptor, have dramatic affects on the perception of the odor of androstenone, a steroid derived from testosterone. 

Interaction between chemical senses 5.8.1 Olfaction-vomeronasal organ interaction... 

We now know that some bird taxa use their sense of smell in foraging. These include kiwis, vultures, seabirds, and honey guides. Others, such as seed-burying birds, and oilbirds, most likely use olfaction for finding food. 

Wolves, Canis lupus, detect prey from 300 (27m) yards or even up to 1.5 miles (2.5 km) downwind by direct scenting, i.e. smelling the air. They may also track initially, followed by direct scenting at close range (Mech, 1970). The same individual may be guided by different senses according to circumstances. For instance, a coyote. Cams latrans, uses mostly vision when finding a rabbit in an enclosed room, and olfaction is least important. Outdoors, however, olfaction becomes more important and the coyote approaches from downwind approximately 84% of the time. In addition, wind may interfere with the sounds of the prey outdoors (Bekoff and Wells, 1980). 

Tester, A. L. (1963). Olfaction, gustation and the common chemical sense in sharks. Sharks and Survival 8,255-282. 

Of the different sensory modalities, olfaction does not appear to feature in reports of the effects of plant hallucinogens. Since olfaction is the one sense not relayed through the thalamus, this brain area is likely to be central to the changes in consciousness described. Many target receptors implicated, e.g. muscarinic, 5-HT2, D2, D3 and opiate, are present in this thalamic nuclei the human brain. 

Human perception of flavor occurs from the combined sensory responses elicited by the proteins, lipids, carbohydrates, and Maillard reaction products in the food. Proteins Chapters 6, 10, 11, 12) and their constituents and sugars Chapter 12) are the primary effects of taste, whereas the lipids Chapters 5, 9) and Maillard products Chapter 4) effect primarily the sense of smell (olfaction). Therefore, when studying a particular food or when designing a new food, it is important to understand the structure-activity relationship of all the variables in the food. To this end, several powerful multivariate statistical techniques have been developed such as factor analysis Chapter 6) and partial least squares regression analysis Chapter 7), to relate a set of independent or "causative" variables to a set of dependent or "effect" variables. Statistical results obtained via these methods are valuable, since they will permit the food... 

---