TASTE BUDS
Sense organs for taste or gustatory sensation are the taste buds. Taste buds are ovoid bodies with a diameter of 50 μ to 70 μ. In adults, about 10,000 taste buds are present and the number is more in children. In old age, many taste buds degenerate and the taste sensitivity decreases.
SITUATION OF TASTE
BUDS
Most of the taste buds are
present on the papillae of tongue. Taste buds are also situated in the mucosa
of epiglottis, palate, pharynx
and the proximal part of esophagus.
Types of papillae located
on tongue:
1. Filiform papillae
2. Fungiform papillae
3. Circumvallate papillae.
1. Filiform
Papillae
Filiform papillae are
small and conical-shaped papillae, situated over the dorsum of tongue. These
papillae contain less
number of taste buds (only a few).
2. Fungiform
Papillae
Fungiform papillae are round
in shape and are situated over the anterior surface of tongue near the tip.
Numerous fungiform papillae
are present. Each papilla contains moderate number of taste buds (up to 10).
3. Circumvallate
Papillae
Circumvallate papillae are large structures present on the posterior part of tongue
and are many in number. These papillae are arranged in the shape of ‘V’. Each papilla
contains many taste buds (up to 100).
STRUCTURE OF TASTE
BUD
Taste bud is a bundle of
taste receptor cells, with supporting cells embedded in the epithelial covering
of the papillae. Each
taste bud contains about 40 cells, which are the
modified epithelial cells.
Cells of taste bud are
divided into four groups:
Type of Cells in
Taste Bud
1. Type I cells or
sustentacular cells
2. Type II cells
3. Type III cells
4. Type IV cells or basal
cells.
Type I cells and type IV
cells are supporting cells. Type III cells are the taste
receptor cells. Function
of type II cell is unknown.
Type I, II and III cells have microvilli, which project into an opening in
epithelium
covering the tongue. This
opening is called taste pore. Neck of each cell is attached to the neck of
other. All the cells of taste bud are surrounded by epithelial cells. There are
tight junctions between epithelial cells and the neck
portion of the type I, II and III cells, so that only the tip of these cells are exposed to fluid in oral cavity.
APPLIED PHYSIOLOGY – ABNORMALITIES OF
TASTE SENSATION
AGEUSIA
Loss of taste sensation is
called ageusia. Taste buds in anterior two thirds of the tongue are innervated
by the chorda tympani branch of facial nerve. Chorda tympani nerve receives taste fibers from tongue via
lingual branch of mandibular
division of trigeminal nerve. So, the lesion in facial nerve, chorda tympani or
mandibular division of trigeminal
nerve causes loss of taste sensation in the anterior two third of the tongue. Lesion
in glossopharyngeal nerve leads to loss of taste in the posterior one third of
the tongue.
Temporary loss of taste
sensation occurs due to the drugs like captopril and penicillamine, which
contain sulfhydryl group
of substances.
HYPOGEUSIA
Hypoguesia is the decrease
in taste sensation. It is due to increase in threshold for different taste
sensations. However, the taste sensation is not completely lost.
TASTE BLINDNESS
Taste blindness is a rare
genetic disorder in which the ability to recognize substances by taste is lost.
DYSGEUSIA
Disturbance in the taste sensation is called dysgeusia. It is found in
temporal lobe syndrome, particularly
when the anterior region
of temporal lobe is affected. In this condition, the paroxysmal hallucinations
of
taste and smell occur,
which are usually unpleasant.
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