The one trillion is probably an underestimation of the true number of smells we can detect, said Vosshall, because there are far more than different types of odor molecules in the world. No longer should humans be considered poor smellers. In fact, new research suggests that your nose can outperform your eyes and ears, which can discriminate between several million colors and about half a million tones. Making Sense of Scents: This image may look like a carnival mask, but it actually shows the key structures mammals use every time they smell.
The Nose Knows Smell begins at the back of nose, where millions of sensory neurons lie in a strip of tissue called the olfactory epithelium.
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A Better Smeller Although scientists used to think that the human nose could identify about 10, different smells, Vosshall and her colleagues have recently shown that people can identify far more scents. The molecular receptive range of an odorant receptor. Buck L, Axel R.
Olfactory system - Wikipedia
A novel multigene family may encode odorant receptors: Humans can discriminate more than 1 trillion olfactory stimuli. Gilad Y, Lancet D. Population differences in the human functional olfactory repertoire. Molecular Biology and Evolution. The dog and rat olfactory receptor repertoires. Seeing Your Sense of Smell. Neuronal filters for broadband information transmission in the brain November 21, Medical Xpress -- As in broadband information technology, the nervous system transmits different messages simultaneously from one brain region to others.
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Their results, appearing December 17 in the journal Current Biology, suggest that lightly brushing Read more Click here to reset your password. Sign in to get notified via email when new comments are made. In addition to the mitral cells, the olfactory bulb is packed with interneurons and modulatory neurons. These critical organizing factors ensure that odor signals are carried to the proper cortical region where chemical messengers impart the sense of smell. However, while this brief description suggests a static scheme of messages and messengers, new discoveries have revealed an incredibly dynamic system.
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Two olfactory sensory neurons expressing the marker GFP, visualized with blue dots representing sensory neurons that express different odor receptors. Photo courtesy of Charles Greer. An expert in central nervous system development and regenerative neural events, Yale Professor of Neurosurgery and Neurobiology Charles Greer has pioneered research into sensory systems, with a particular focus on the olfactory system.
Greer emphasized the precocious and inherently complex nature of olfaction, citing that the first vestiges of the olfactory system, the olfactory placode, are evident as early as embryonic day nine in the mouse. Through his work, Greer has uncovered an extraordinary plasticity in the olfactory system. While most of the other sensory systems — including the visual, auditory, and somatosensory systems — have a fixed and limited number of receptors, the receptors of the olfactory system undergo constant renewal.
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Odor receptors, the only portion of the central nervous system directly exposed to the environment, are particularly prone to damage from toxins or even dust, requiring renewal within six to ten weeks of exposure. Current investigations have revealed a population of olfactory stem cells that are capable of giving rise to new sensory neurons that can differentiate and guide their axons to the appropriate site on the olfactory bulb.
Nevertheless, their recent discovery has left many questions still unanswered. There is no clear approximation for the size of the stem cell population, although Greer proposes an estimate of a base population of , stem cells.
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Furthermore, whether the stem cells are truly pluripotent or specific to particular receptor families remains unknown. Highly detailed imaging studies suggest that the proliferative region of the brain that gives rise to the neurons — the sub-ventricular zone — retains its developmental capabilities, producing 10, to 30, new neurons every day. These new neurons migrate into the olfactory bulb and become integrated into the synaptic circuitry of the olfactory system.
The mechanisms and factors that guide these developing neurons are only now being uncovered. Photo courtesy of Yale Department of Neurosurgery. In order to comprehend how the daughter neurons from olfactory stem cells are able to migrate to a precise location on the olfactory bulb or in the nasal epithelium, the development of the olfactory system must be understood.
Map of brain connections provides insight into olfactory system
A leading theory Greer supports is the existence of developmental protomaps. These protomaps function as design schemes in which cellular fate is determined at the time of cellular division. Protomaps have been implicated in the development of the neocortex, especially in primates, where specific topographical birth sites lead to a particular neuronal fate in a designated site in the neocortex. While debate remains on whether or not there exists an odor receptor or olfactory bulb map, research conducted within the Greer lab suggests that there are indeed protomaps for both odor sensory and odor processing regions and that these maps develop in a parallel but independent manner.
Fumiaki Imamura, a postdoctoral associate with the lab, demonstrated one critical aspect by proving that both a spatial and temporal protomap determines the fate of mitral cells, which carry information from the olfactory bulb to the cortex. Although the particular mechanisms that control this fate determination are not yet fully known, there have been several stunning discoveries.