The smell detector
Detecting odours is one of the nose’s tasks. Most
people can recognize about 4000 different scents. The really
sensitive nose can go up to about 10,000. Since the sense
of smell is not very important, it is subdued and often
unused. But this sense is of much help to a person born
deaf and blind. The nose is then a key tool of identification
and can efficiently be used to recognize people, houses
and rooms by scent alone.
On the roof of each of the nose’s nasal cavities is
a patch of yellow-brown tissue smaller than a postage stamp.
Each patch has roughly ten million receptor cells, and six
to eight tiny sensory hairs that project from each cell.
All this apparatus is connected to the brain, three centimetres
away. When something smelly is in the vicinity of the nose,
the receptor cells are triggered to release a small wisp
of electricity. These signals are carried to the brain,
which then interprets the smell.