L14 & L15 - Tongue 1/2 Flashcards
Gustatory system
Detects, identifies and determines the palatability of tastants (sugars,
salts, acids, alkaloids, amino acids)
Distinguishes between safe and nutritious foods and potentially
dangerous substances (poisons etc)
Taste is a chemical sense but perception of flavour requires input from
multiple systems and integrating information such as smell, memory,
hunger, satiety and visceral states.
Taste transmission involves
– Receptor (taste bud)
– Cranial nerves
– Nucleus solitarius (brainstem)
– Thalamus
– Gustatory cortex
Taste Receptors
Located on taste buds in the
mouth, pharynx and epiglottis
Taste buds on the tongue
embedded in the circumvallate,
fungiform and foliate papillae
Circumvallate papillae
10-12 papillae - anterior to sulcus
terminalis
*Contain over half the taste buds of the
tongue
*Taste buds located on the sides of the
papilla
*Each papilla surrounded by a deep trench
*Ducts of Von Ebner salivary glands open
into the trench. They secrete
1. Serous saliva - why?
2. Lipase – why?
* Abrasion of posterior tongue against hard
palate in mastication opens the trench -
fluids containing tastants are directed to
taste bud
Fungiform papillae
Mushroom shaped papillae
scattered over anterior 2/3 of
tongue
- Each papillae contains 6-8
taste buds
Foliate papillae
Epithelial folds on the lateral aspect of the tongue
near the palatoglossal arch and medial to the
molars
Taste buds located within the folds – therefore
tastants must enter cleft to reach the taste buds.
Mechanical motion of chewing helps direct the
tastants down the folds
Fewer foliate papillae in humans compared to other
species
Filiform papillae
Filiform most numerous of
papillae – don’t contain taste
buds.
* Shape of fir tree
* Allow soft substance to be
licked into the mouth (eating
ice cream)
Taste receptor distribution
Most of tongue and other
taste organs are sensitive to
all basic tastes
Some areas posses a greater
abundance of receptors that
are specific for a particular
taste
* sweet – anterior tongue
* sour – lateral tongue
* bitter – posterior tongue and
epiglottis
Taste Buds
Goblet shaped structure
Presents a taste pore that opens into
the oral cavity
Contain 50-75 cells
3 cell types
– Gustatory cell
– Sustentacular cell (supporting)
– Basal cell
Look at diagram
Taste
Chemical sense - 5 basic qualities detected:
* Sweet - sugar
* Salty - sodium ions
* Bitter - acidity
* Sour - alkalinity
* Umami - amino acids
Flavour
Flavour is the perceived taste - Information integrated with input from the multiple systems; smell, touch, temperature, nociceptive information and more
Gustatory cell
10-14 day life span
Microvilli extend from apical end of
gustatory cell into taste pore
Taste receptors on microvilli
Nerve fibres enter at base of taste
bud and wrap around the gustatory
cell
Stimulation of taste receptors
Direct pathway
Indirect pathway
Direct pathway of taste reception
Chemical flows via sodium
channels into the receptor cell.
2. ↑positive charge → activation
of voltage gated Ca2+ channels
3. → Ca2+ influx and
neurotransmitter release
Indirect pathway of taste reception
- Chemical binds to receptor (G
protein) - G protein releases α subunit
- → inositol triphosphate (IP3)
- → ion channel activation → Na+
influx - → deploarization of cell
membrane, influx of Ca2+, and
neurotransmitter release
Taste pathway
Chemical
stimulation
of taste bud
Synapse between
gustatory cell and
1
st order neurone
First order neurone
* facial nerve
* glossopharyngeal nerve
* vagus nerve
Nerve cell body of
2
nd order neurone in
the gustatory
nucleus of brain
stem
Synapse between
1
st and 2nd order
neurones
Nerve cell body of 3rd
order neurone in the
ventral posterior nucleus
of the thalamus
Synapse between
2
nd and 3rd order
neurones
Projects to gustatory
cortex
