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
Cranial nerves involved in taste reception
Facial nerve (CN-VII)
Glossopharyngeal nerve (CN-IX)
Vagus nerve (CN-X)
Facial nerve
Motor to muscles of facial expression
* Parasympathetic to submandibular & sublingual
salivary glands, lacrimal glands & nasal mucosa
* General sensation from skin around ear
* Taste from anterior 2/3 of tongue & soft palate
Taste transmission via facial nerve
- greater petrosal
nerve - passes
through
pterygopalatine
fossa
enters skull at
an unnamed
foramen - chorda
tympani (initially
travels from tongue
with lingual nerve of
V3)
enters skull at the
petrotympanic
fissue
*J oins main part of
facial nerve in
petrous temporal
bone. Sensory
nerve cell body
located in
geniculate
ganglion
- enters cranial
cavity at internal
auditory meatus - enters brain
stem as the
nervus
intermedius
at the pons
medullary
junction - Passes in
tractus
solitarius to
terminate in the
nucleus
solitarius
Glossopharyngeal nerve
Motor to stylopharyngeus
* Parasympathetic to parotid gland
* General sensation from posterior 1/3 tongue,
pharynx, parts of ear
* Visceral afferent from carotid body & sinus
* Taste from posterior 1/3 of tongue & pharynx
Taste transmission via glossopharyngeal nerve
glossopharyngeal
nerve (posterior 1/3 of tongue and pharynx)
enters skull at
jugular
foramen
Sensory nerve cell bodies located
in superior & inferior
glossopharyngeal ganglia
enters brain stem at
the medulla
Passes in tractus
solitarius to
terminate in the
nucleus
solitarius
Vagus nerve
Motor to muscles of pharynx & larynx
* Parasympathetic to organs of abdomen and
heart
* General sensation from larynx and parts of ear
* Visceral afferent from thoracic and abdominal
viscera and aortic body & sinus
* Taste from epiglottis
Taste transmission via the vagus nerve
Vagus nerve (epiglottis)
enters skull at
jugular
foramen
Sensory nerve cell bodies
located in inferior vagal
ganglion (nodose)
enters brain stem at
the medulla
Passes in tractus
solitarius to
terminate in the
nucleus
solitarius
Nucleus solitarius
Located in the medulla
Recieves visceral afferent
fibres from facial,
glossopharyngeal & vagus
nerves
Taste fibres terminate in
the gustatory nucleus at
the rostral end
Ascending pathway of the gustatory system
watch leccy
Axons of the 2nd order
neurones ascend in the
ipsilateral central
tegmental tract, pass
through pons and
midbrain to the thalamus.
thalamus
Terminate in the
ventral posterior
nucleus of thalamus
Axons of the 3rd order neurone project to the
gustatory cortex
Located in the insular cortex and operculum
Gustatory cortex also receives input from
* Limbic system (amygdala)
* Lateral hypothalamus
* Prefontal cortex
* Olfactory areas
* Other regions of insular cortex -
nociceptive, visceral, somatosensory and
auditory signals
