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lec25reading - Chemical Signals 5. Reception of chemical...

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Unformatted text preview: Chemical Signals 5. Reception of chemical stimuli is based on the temporary binding of odor- ant molecules to specific protein-receptor molecules in a cell or chemosen— sory organ. The receptor protein changes in shape or in chemical composi- tion. Either change initiates a cascade of biochemical reactions that ultimately leads to a nerve impulse. Nerves from the chemosensory cells are collected in a ganglion or olfactory bulb, where summation and initial processing of the sensory input occurs before it travels on to the brain. Chemosensory cells have a short life span and are continuously being re- placed by new cells. 6. The ideal chemosensory organ is both highly sensitive to low concentra- tions and responsive to a wide range of chemicals. High sensitivity is achieved with a labeled line coding system responsive to a narrow range of chemicals. A broad response spectrum is achieved with an across-neu- ron pattern coding system involving many receptor types sensitive to dif— ferent features of molecular structure. Since these represent an incompati- ble tradeoff, long-distance chemical sex attractants employ the labeled line strategy, whereas generalized food and olfactory receptors employ the across-neuron pattern strategy. 7. Arthropods have olfactory, taste, touch, and current detectors located on their paired antennae, and contact (taste) receptors on their mandibles, legs, and feet. The olfactory receptor in fish is a flow—through organ sepa- rated from the respiratory system, and taste receptors are located around the mouth. In terrestrial vertebrates, the olfactory system is a duct in the respiratory system, with the lungs functioning to draw air into the olfac- tory organ. Many vertebrates also possess a contact receptor, the vomeronasal organ, located in the roof of the mouth. 8. The only type of directional information an olfactory receiver has for ori— enting itself in a diffusion-based chemical stimulus field is an intensity gradient, Where the concentration of the chemical decreases with distance form the source. Receivers can move up or down the gradient using sim— ple kinesis mechanisms, or they can use sequential or simultaneous sam— pling methods to actually detect the direction of the gradient. In a current— dispersed chemical field, receivers can use the associated current flow direction to approach or avoid the sender. FURTHER READING Wilson (1963) provided one of the first short nontechnical overviews of olfactory signaling in animals, and Agosta (1992) is a recent layperson’s review of chemical signaling. Chapters 4 and 7 of Dusenbery (1992) give the most recent description of chemical signal properties, transmission, production, and reception. Although the focus of Atema et a1. (1988) is on aquatic sensory systems, the chapters dealing with chemical stimuli (1~2) and reception (11—15) provide excellent reviews rele- vant to communication in air as well. Summaries of gland structure may be found in Quay (1977), Brown and Macdonald (1985) and Wilson (1971). The classic diffu- sion models are outlined in Sutton (1953) and Wilson and Bossert (1963). Tennekes 317 318 Chapter 10 and Lumley (1990) is a good introductory text on turbulence. Invertebrate pheromones and chemical reception are described in several multiauthor books, including Birch (1974), Birch and Haynes (1982), Bell and Carde (1984), and Payne et a1. (1986). Schneider (1964) and Kaissling (1971) review insect antennae. A simi- lar set of books describes vertebrate chemical communication, including Miiller— Schwarze and Mozell (1977), Duvall et a1. (1986), Stoddart (1980), Vandenbergh (1983), Albone (1984), Brown and Macdonald (1985), and Bruch et a1. (1988), Re- cent work on neurological and molecular reception in vertebrates is reviewed by Buck (1996). Good descriptions of the vomeronasal organ may be found in Halpern (1987), Hart (1983), and Wysocki et a1. (1980). Orientation in a chemical field is discussed by Dusenbery (1992), Kennedy (1986), and David (1986). Finally, a multivolume series on olfaction and taste illustrates the developing knowledge of these modalities over the years, with Roper and Atema (1987) being among the more useful volumes. ...
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This note was uploaded on 10/28/2010 for the course BIEB 166 taught by Professor Nieh during the Spring '09 term at UCSD.

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lec25reading - Chemical Signals 5. Reception of chemical...

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