The biological process
of smelling (olfaction) is thought to be a type of chemical reaction between
"receptors" in the nose and the molecules of interest. Receptors are
molecular level areas or sites on which molecules of given structural shapes
can adhere electrostatically. The changes in charge distribution around the
site seem to be enough to trigger the sensory signals to the brain giving the
sensation of smell. ( More: -ref1,
ref2
The first is an excellent link)
Smell is not really understood - none of the processes of molecular interaction with receptor sites are fully understood whether they be in the brain or elsewhere.
Smell is unusual in that of all the senses, it is the only one that cannot be "remembered" - a visual scene can be remembered visually, sound can be recalled but not smell. BUT the brain does recognise smells and these trigger powerful memories.
Evidence is accruing that smell operates at background levels for humans as well as the obvious levels, especially for recognising family and in the selection of human mates. Pheromones - molecules that elicit biological responses- have been discovered for humans and a vomeronasal organ has been confirmed in human noses. This organ, which is clear in most other animals, was only confirmed in the late 1980's as existing in humans. So much for anatomy! The organ has been shown to link to pheromone activity in other animals.
Taste is thought to be about 75% smell. Generally foods taste as they smell but clear exceptions do occur. The durian fruit of Indonesia and Malaysia smells putrid but has a delicious taste.
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