2004 buck-lecture - UNRAVELING THE SENSE OF SMELL Nobel...

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Unformatted text preview: UNRAVELING THE SENSE OF SMELL Nobel Lecture, December 8, 2004 by Linda B. Buck Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 981091024, USA. INTRODUCTION The subject of my lecture is the sense of smell, one of the five senses through which we perceive the world. Through the sense of smell, humans and other mammals can perceive a vast number and variety of chemicals in the external world. It is estimated that humans can sense as many as 10,000 to 100,000 chemicals as having a distinct odor. All of these odorants are small, volatile molecules. However, they have diverse structures and somehow those diffe- rent structures are perceived as having different odors (Figure 1). The sense of smell is mediated by the olfactory system, a system that is char- acterized by exquisite sensitivity and discriminatory power. Even a slight change in the structure of an odorant can change its perceived odor. For example, the close relative of a chemical that is perceived as pear can have the scent of an apple. In addition to odorants, the olfactory system detects pheromones, chemicals that are released from animals and act on members of the same species, stimulating hormonal changes or instinctive behaviors, such as mating or aggression. The olfactory system also detects predator odors, which can elicit innate fear responses. Over the past 16 years, our work has focused on two questions. First, how do mammals detect so many different environmental chemicals? And second, how does the brain translate those chemicals into diverse odor perceptions and behaviors? Odorants are initially detected by olfactory sensory neurons, which are located in the olfactory epithelium lining the nasal cavity (Figure 2). These neurons transmit signals to the olfactory bulb of the brain, which then relays those signals to the olfactory cortex. From there, olfactory information is sent to a number of other brain areas. These include higher cortical areas thought to be involved in odor discrimination as well as deep limbic areas of the brain, which are thought to mediate the emotional and physiological effects of odors. In contrast to odorants, pheromones are detected primarily in the vomeronasal organ, or VNO, a separate olfactory structure in the nasal septum. 267 268 Figure 1 . Humans and other mammals perceive a vast number of chemicals as having distinct odors. Figure 2. The olfactory pathway. Odorants are detected by olfactory sensory neurons in the olfactory epithelium. Signals generated in those neurons are relayed through the olfactory bulb to the olfactory cortex and then sent to other brain areas. From VNO neurons, signals are relayed through the accessory bulb to the medial amygdala and then the hypothalamus, areas implicated in hormonal and behavioral responses to pheromones....
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2004 buck-lecture - UNRAVELING THE SENSE OF SMELL Nobel...

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