40. How do we taste and smell things?
Our nose and mouth have special receptor cells, which when
stimulated by chemical molecules, send nerve impulses to the brain.
Our tongue is covered with tiny growths or papillae. Some papillae
contain small group of cells known as taste buds. Each taste bud
contains four to twenty receptor cells with short sensory hair.
These hair react to molecules dissolved in the saliva. We can taste
four main kinds of tastes.
Bitterness is tasted at the back of the tongue, sourness at the sides,
sweetness at the front and saltiness can be tasted all over. Our nose
has cell receptors at the roof of the nasal cavity. These receptors have
sensory hair that branch and project into the mucus that lines the
cavity.
Molecules in the air dissolve in the mucus and stimulate these hair.
There are about 15 kinds of smell receptors which can detect over
10,000 different smells.
