The receptors are of five main types. These are mechanoreceptors, photoreceptors, chemoreceptors, electroreceptors and thermoreceptors. Chemical receptors are of two types :taste bud for taste and Olfactory cells for smell.
Taste receptors(Gustatoreceptors): The receptor cells for taste (gustation) occur in groups called taste buds. The taste buds mostly lie in the mucous membrane that lines the grooves around the papillae on the tongue. A papilla may contain a few to about a hundred taste buds, and there are about 10000 taste buds on the entire tongue. Some taste buds also occur in the mucous membrane of the pharynx, palate and epiglottis. Another name for taste buds is gustatory sensillum.
Olfactoreceptors (Smell receptors): Olfactory sensation is the most primitive of all special senses and is much more acute than taste. The receptors for smell occur in small patch of olfactory neuroepithelium, located in the roof of the nasal cavity.
Difference between Taste cells and Olfactory
cells
Taste cells
(Gustatoreceptors)
|
Olfactory cells or Smell receptors
(Olfactoreceptors)
|
Occur in taste
buds on tongue, palate, epiglottis, and pharyngeal wall.
|
Occur in a
small patch of olfactory epithelium lining the roof of nasal cavity.
|
Only taste the
food
|
Smell as well
as taste the food.
|
Are specialized
epithelial cells. (Secondary sense cells)
|
Are bipolar
neurons (primary sense cells).
|
Are crescentic
in form.
|
Are spindle
shaped in form.
|
Free ends taper
and bear microvilli which have receptor sites for taste producing molecules.
|
Free ends of
dendrites enlarge into vesicles that bear non motile cilia carrying receptor
sites for odoriferous substances.
|
Sensory nerve
fibres form synapses on the surface of taste cells.
|
Axons of
olfactory cells act as sensory fibres.
|
Taste cells
function only as sensory receptors.
|
Olfactory cells
function as sensory receptors as well as conducting neurons.
|
Are stimulated
by chemicals that come in their contact in relatively high concentrations.
|
Are stimulated
by chemicals from a distance and in much lower concentrations.
|
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