“To-day I think
Only with scents, – scents dead leaves yield,
And bracken, and wild carrot’s seed,
And the square mustard field;
Odours that rise
When the spade wounds the root of tree,
Rose, currant, raspberry, or goutweed,
Rhubarb or celery;
The smoke’s smell, too,
Flowing from where a bonfire burns
The dead, the waste, the dangerous,
And all to sweetness turns.
It is enough
To smell, to crumble the dark earth,
While the robin sings over again
Sad songs of Autumn mirth.”
– Edward Thomas, Collected Poems
Odours. Smells. Fragrances!
People, animals, birds, insects; all living beings have a strong sense of smell. We can identify the source based on the odours we perceive before we can even see it. Certain smells can also evoke beautiful and powerful memories of places, food, things and even people.
All of this is possible due to the olfactory receptors present in our body. Receptors are protein molecules sitting on the surface of cells that receive chemical signals from outside the cell. The chemical molecule attaches to a specific receptor, just like how a key fits into a specific lock, and induces certain responses in the cell.
The olfactory receptors belong to a family of receptors called G-protein coupled receptors. Last week, the Nobel Prize in Chemistry was awarded to Robert J. Lefkowitz and Brian K. Kobilka for their ground breaking studies performed over four decades on how the body responds to external stimuli such as taste, smell, sight etc . They were responsible for discovering the G-protein-coupled receptors (in 1980s) which are involved in several physiological processes such as sensory detection and mood regulation.
Olfactory receptors are responsible for the detection of odour molecules. Mammals have over 1000 different olfactory receptors, each of which detects a few different odours, usually with similar molecular structure. The odour molecule attaches to its specific receptor and activates certain processes in the cell which in turn sends signals to the brain that perceives and identifies the odour.
Incidentally, in 2004, scientists Linda Buck and Richard Axel won the Nobel Prize in medicine for cloning an olfactory receptor.