Organs of Smell and Taste
Smell:
In human the
receptors for the sense of smell are called olfactory cells located high in the
roof of nasal cavity.
Olfactory cells
are actually neurons that synapse with the nerve fibres making up the olfactory
nerve. Each olfactory cell has cilia, which are stimulated by many chemicals in
the air. Research resulting in the stereochemical theory of smell has shown
that different smells may be related to the various shapes of the molecules
rather than to the atoms that make up the molecules. These shapes fit specific olfactory
sites on the olfactory cells cilia.
The sense of
smell is generally much more acute than the sense of taste. Human nose, for
example can detect one 25 millionth of 1 mg of mercaptan, the odoriferous
chemical given off by a skunk. This averages out to approximately one molecule
per sensory ending. Yet humans have a weak sense of smell compared to other
vertebrates, such as dogs.
Taste:
The receptors
for the sense of taste in mammals are the taste buds. Most of these are located
on the tongue but they also present on the surface of the soft palate, pharynx
and epiglossis. Each taste bud contains number of elongated cells. These cells
have microvilli which project through the taste pore an opening in the taste
bud. It is the micro villi that stimulated by various chemicals in the
environment.
Humans are
believed to have four types of taste buds, each type stimulated by chemicals
that result in a bitter, a sour, a salty or a sweet sensation.
The sense of
taste and the sense of smell supplement each other, creating a combined effect
when interpreted
by the cerebral cortex. For example when you have a cold, food
seems to lose its taste but actually the ability to sense its smell is
temporarily absent. This may work in reverse also. When we smell something,
some of the molecules move from the nose down into the mouth and stimulate
certain taste buds. Thus, part of what we refer to as smell is actually taste.
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