Ask A Scientist© Biology Archive

Author:      matkru
Text:        How does the nose distinguish between different smells?  What 
exactly is it smelling anyway and is there any way to reproduce this?

Response #:  1 of 1
Author:      Jim Murray
Text:        The nose distinguishes between different smells via the nasal 
epithelium at the top of you nasal pharynx.  That is a delicate membrane 
innervated by many nerve cells.  Each nerve cell has many proteins embedded in 
its cell membrane.  These proteins have complimentary shapes to certain 
chemical groups that elicit scents.  When an odorant molecule binds to one of 
these proteins, the cell depolarizes (due to a second messenger system in the 
membrane).  This depolarization propagates back to the part of the brain 
called the olfactory bulb, below the forebrain.  There the information from 
different cells is sorted out and sent to other brain structures, and the 
subjective sense of "smell" is elicited.  Distinguishing between different 
odors is possibly accomplished by comparing different inputs from nerve cells 
with different protein receptors in them, or by "labeled lines" of neurons


with a mix of proteins in them that are complimentary to a mix of odorant 
molecules that make up a scent.  I know of know mechanical process that 
approximates smell by spectroscopy can distinguish different molecules The 
answer I have given is for vertebrates but invertebrates and plants can also 
smell, although by different mechanisms.  Smelling in general is the 
subjective sensation experienced when one's olfactory system detects a scent; 
it can not be approximated by any mechanical process that I am aware of, 
although spectroscopy can be used to distinguish between chemical milieus.