olfactory system

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Offline t360

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olfactory system
« on: 12/04/2005 19:09:17 »
Why don't we  recognize odours that we smell on a daily basis?  For example, when one begins working in a new environment, the aromas are new for a period of time.    Is there a way to refresh the receptors after the "newness" wears off?  


Offline chris

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Re: olfactory system
« Reply #1 on: 13/04/2005 17:44:19 »
Great question, and one which underlies one of the most important processes in the whole nervous system and its dynamic nature.

The olfactory system comprises a cluster of 'hair cells' on the olfactory epithelium at the top of the nose. These hair cells express receptors, like docking stations, for smell molecules, called odourants, that are dispersed in the air.

These docking stations are specific for certain odour chemicals, and when an odour is present it locks onto the receptor and activates the hair cell which in turn activates a secondary nerve cell which relays the presence of the smell to the brain.

The 'smell' that we experience is therefore the sum total of the cocktail of odours that the brain detects. A good analogy is coloured light. By varying the amount of red, green, blue, yellow light you can change the colour that you see.

So why do odours appear to become less strong after we have been smelling them for a while ? This is down to a process called 'adaptation' and you find this at work in every sensory system in the body. If you touch something warm you'll eventually cease to notice that it is warm; look at something without letting your eyes move for more than a few seconds and the image will begin to degrade; and the reason we're not aware of the clothes we wear is because the nervous system quickly stops noticing them.

In essence the process of adaptation is there to prevent sensory overload. What the nervous system is really interested in are things that are changing. So our senses are dynamic - they quickly 'tune out' to things that remain the same to avoid wasting brain power and distracting our attention with information that is not important.

In the context of smell, scientists in the US worked out a few years ago how the olfactory system adapts to the long term presence of an odour - a molecule on the sensory hair cells switches off their action after a short time.

Therefore, to restore smell you need to merely change the ambient smells you are experiencing for a short while to reactivate the response to the usual ones to which you have become 'adapted'.


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I never forget a face, but in your case I'll make an exception - Groucho Marx


Offline NakedScientist

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Re: olfactory system
« Reply #2 on: 14/04/2005 10:53:36 »