All of us are aware of the five senses: hearing, touch, sight, taste and smell, but so often is smell taken for granted. You are constantly seeing, touching and hearing something, but it is unlikely that youâ??re constantly smelling a new smell (taste relies upon smell) and therefore this sense is thought of as unimportant in observing your surroundings. However, the fact that smell usually needs to be consciously activated may make this sense even more specialized. To initiate smelling, one must sniff, usually a faster inhalation of air, which allows for odor molecules to reach odor receptors within the nose. By doing this, it is even possible to regulate the amount of molecules that reach these receptors, such as by increasing either the time, or amplitude of said sniff. It is even theorized that the simple act of sniffing, as opposed to regular breathing patterns, activates olfactory receptors within the nose which are not normally active at all times.
This specialized system of respiratory inhalation in order to smell has further differentiated humans from other animals and may lead to an evolutionary advantage. We have the ability to breathe without consciously smelling. This is partially due to the fact that our olfactory receptors are only activated due to increases in length and amplitude of inhalation, but this is not to say that some pervasive smells donâ??t force these receptors to react to their presence. This is usually because new smells are compared to those in the background, and therefore odors significantly different from pre-existing scents in the environment. However, animals such as rats are unable to differentiate the unimportant background smells and must constantly smell every molecule that passes their nose. Further specialization of human olfactory systems have allowed us to smell not only upon inhalation but also during exhalation. While the thought that we can discern our own scent of exhalation, this ability is what allows for much of our sense of taste. Taste is almost entirely due to our ability to smell food as we eat it. This is due to the fact that smells travel up the back of the throat and can then affect olfactory sensors. Without this ability, it is unlikely that rats would have a similar sense of taste. This specialized respiration also seems to help evolutionarily, as humans are able to ignore unimportant scents, and concentrate specifically on those which are entirely different to our current surroundings.
There is even evidence that the continued act of sniffing increases the size of dendritic spines and overall synapses in conjunction with olfactory receptors. This increase can lead to a superior ability to smell in the long run.
Smell is an important sense. Without the ability to smell, we wouldnâ??t be able to taste, or to use important environmental clues to better survive. These clues can be as simple as an acrid smell, alerting one to a noxious contaminant or even a sweet, sugary smell of fruit, which indicates a food which we can eat without being poisoned.
- All in a Sniff, Published in Neuron, found at: http://www.sciencedirect.com/science?_ob=MiamiImageURL&_cid=272195&_user=918210&_pii=S0896627311007859&_check=y&_origin=gateway&_coverDate=22-Sep-2011&view=c&wchp=dGLzVlk-zSkWz&md5=9a1a4cb0c581b40b58f5787b7c26e1ff/1-s2.0-S0896627311007859-main.pdf
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NRSC 4132 BlogA GROUP WEBLOG FOR NEUROPHARMACOLOGY NRSC 4132
November 8, 2011
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