Many animals live in a world dominated by smells. Probably this was the first of the senses to develop.
In the human face, the outside nose is obvious. But there is another nose in the upper nostrils. On its sides, a spot about the size of a nayapaisa, contains special nerve cells. Even though our nose cannot distinguish smells very well, it can detect remarkably minute concentrations of odours. The chemoreceptors lie there. Embedded in this tissue are several million chemoreceptors. They are long, thin cells with hair-like cilia forming a web lying on the surface of the tissue that is bathed in mucus. These receptors are connected to a part of the brain called olfactory bulb. The olfactory bulb of a dog is muchg larger than that of man!
The scent molecules pass from the air travelling up the nose to the mucus, where they stimulate the chemoreceptors. The smell centre in the brain receive the messages and tell us what we are smelling.
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