The Physics of Smells?

[misogynisticfeminist]

Where do smells come from? How are they formed? Is there any physics behind smells or none at all? can't seem to find any though so far.

[Integral]

Smells are more physiology and chemistry, so I pop this over to the biology forums. They may have some better answers.

[misogynisticfeminist]

Smells are more physiology and chemistry, so I pop this over to the biology forums. They may have some better answers.

I see.....thanks....

[Vance]

Where do smells come from? How are they formed? Is there any physics behind smells or none at all? can't seem to find any though so far.
Why do you want to know about smells? What are you doing exactly ? I used to ask some questions about smells but I have not got any answers, I would be really angry if someone posts help you out :tongue2:

[Moonbear]

Smells come from the binding of airborne chemicals with odor receptors.

Cell Mol Life Sci. 2004 Feb;61(4):456-69.
Olfactory receptors.
Gaillard I, Rouquier S, Giorgi D.

IGH, CNRS UPR1142, rue de la Cardonille, 34396 Montpellier, France. gaillard@ensam.inra.fr

Olfaction is an ancient sensory system allowing an organism to detect chemicals in its environment. The first step in odor transduction is mediated by binding odorants to olfactory receptors (ORs) which belong to the heptahelical G-protein-coupled receptor (GPCR) superfamily. Mammalian ORs are disposed in clusters on virtually all chromosomes. They are encoded by the largest multigene family (approximately 1000 members) in the genome of mammals and Caenorhabditis elegans, whereas Drosophila contains only 60 genes. Each OR specifically recognizes a set of odorous molecules that share common molecular features. In mammals, signal transduces through the G-protein-dependent signal pathway in the olfactory sensory neurons that synapse ultimately in the glomeruli of the olfactory bulb, and is finally processed in higher brain structures. The expression of a given OR conditions neuron and glomerulus choices. To date, the processes which monitor OR expression and axon wiring have emerged but are not completely elucidated.

Publication Types:
Review
Review, Tutorial
PMID: 14999405 [PubMed - indexed for MEDLINE]

It's kind of late for me here now, so I'm not going to look up any more articles tonight, but I recall from a seminar I attended that odor signals are also context-dependent. In other words, the same odorant chemicals are present in both microwave popcorn and vomit, or possibly it's the same receptors for similar chemicals (I will need to double check the details) , so if you hear the popcorn popping, you smell popcorn, and if you see vomit, you smell vomit, but if you don't have proper context cues, your own perceptions could tell you it's either. The woman who presented the seminar was French and used the microwave popcorn example (first time she smelled it, she thought it smelled like vomit), along with the example of stinky French cheese that she loves and her students think smells like stinky feet.

Vance, I don't remember seeing your post about smells. Maybe I missed it, or maybe you asked a slightly different question I couldn't answer.

[pervect]

Where do smells come from? How are they formed? Is there any physics behind smells or none at all? can't seem to find any though so far.

Well, the concepts of vapor pressure (of solids and liquids) is clearly relevant to the origin of smells, and diffusion describes how smells propagate.

[Phobos]

Where do smells come from? How are they formed? Is there any physics behind smells or none at all? can't seem to find any though so far.

A simplification of what has already been said...

Particles or chemical fumes (i.e., very tiny particles or molecules) emitted from the smelly thing, transmitted through the air to the receptors in your nose which then send a signal to your brain which then interprets it.

[misogynisticfeminist]

hey thanks for the replies. I didn't really know that smells are so context-dependent. I was thinking something like a spectrum of smells or something, ROYGBIV-esque, with wave-lengths stuff like that. But anyway, thanks alot..

[Moonbear]

hey thanks for the replies. I didn't really know that smells are so context-dependent. I was thinking something like a spectrum of smells or something, ROYGBIV-esque, with wave-lengths stuff like that. But anyway, thanks alot..

Well, in terms of the chemical that is released into the air, that's going to be the same every time, and so is the receptor in the nose that it binds to. What is different is just how we interpret the smell based on the context of our experiences. With light perception, a similar idea would be three people viewing something in the violet range of the spectrum, one says it's violet, another calls it grape and a third says it's purple. The wavelength is the same, the photoreceptors in the eye that process that wavelength is the same, it's just what the brain associates it with during processing of that information that determines what name someone would give to the color.

[Nereid]

How different are the non-mammalian smell mechanisms (from mammalian and from each other)? Do plants have a sense of smell?

If an animal has a 'keen sense of smell' (cf Homo sap.) is this principally because it has more receptors, more types of receptors, better brain wiring (e.g. lower threshhold for responding to OR signals), more sensitive receptors, or something else?

[Moonbear]

Humans seem to have a pretty poor sense of smell compared to other animals. Think of how dogs can track the scent of a missing person or fugitive when humans can't detect anything. I've never looked into why this difference exists in any depth. There are a few things that may contribute. The olfactory bulbs of the brain are proportionately much larger in other mammalian species than they are in humans. Most other mammals have a far more developed accessory olfactory system as well (this seems more vestigial in humans, though there are some indications we may still detect some pheromonal signals with it, but not nearly with the same efficiency as other species)...this includes the vomeronasal organ, which is the primary sensory organ for detecting pheromonal cues in other mammals.