Chapter 4

Chapter 4 - Chapter 4 The Chemosensory systems Taste and...

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Chapter 4- The Chemosensory systems: Taste and Smell A. General Characteristics of Chemosensory Perception What evolutionary factors led to the development of chemosensory systems? - Earliest organisms (living in the sea) did not have vision or hearing, but relied on detection of chemicals in the environment for navigation, protection, and feeding. - One basis for distinction among chemosensory systems is whether the mechanisms involved detection of chemicals at a distant source (ancient sea-life equivalent of smell) or in close proximity (equivalent of taste). - Evolution of taste and smell became further refined when terrestrial life forms emerged. - Besides food-seeking and sampling, chemosensory development was also influenced by sociobiological factors: marking territory, interaction w/ others, mating signals, etc. - Pheromones: chemicals secreted by glands to signal sexual receptivity/ attract mates. Why are we sensitive to chemicals? - Humans rely much less on chemosensory info than other species; we are largely visual. - Freud speculated that primate evolution to upright posture resulted in diminished importance of smell (as we physically turned away from the earth). - Some have argued that the course of humanity would be unaffected if we lost the senses of taste + smell; however, even if we do not use them for survival, they have social importance. - Human infants can detect odors of their mother’s breast; are attracted to these, repulsed by scent of strangers. o Olfactory maternal attraction = evidence of human pheromonal system. - Also: menstrual synchrony phenomenon (McClintock effect). - Postulated sources of pheromones in adults: oral cavity, vaginal emissions, and secretions from the apocrine glands in the armpit. - It can be argued that taste provides survival value through its use in rejecting foods that are likely to be poisonous because of a bitter or sour taste. - Our craving for salt, which is essential to survival, may reflect need for ensuring enough of it is consumed. On the other hand, the unpleasant taste of too much salt may act as a system of preventing too much intake, which is also unhealthy. How does human chemosensory function differ from that of other animals? - The differences are most apparent in the domain of olfaction. - Vomeronasal organ : (VNO) a specialized organ evolved to detect pheromones; located in the nasal cavity but separate from the main olfactory organ. o Presence of a functional VNO in humans remains controversial, despite evidence. - Humans also have reduced olfactory system sensitivity, which correlates w/ the reduced survival function of smell. E.g. dogs are 10,000x more sensitive to smell than humans. How do taste and smell differ from the other sensory systems?
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Chapter 4 - Chapter 4 The Chemosensory systems Taste and...

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