Question:
How does the nose distinguish between different smells? What
exactly is it smelling anyway and is there any way to reproduce this?
Replies:
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.
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