gustatory system

Question 1

what does the gustatory system do

Answer 1

-detects, identifies and determines the palatability of tastants
- distinguishes between safe and nutritious foods and potentially dangerous substances

Question 2

taste

Answer 2

taste is a chemical sense
- To perceive The Taste often We require input from multiple systems and integrating information such as smell, memory, hunger, satiety, and visceral states
- So if you lose your sense of smell your taste will not get cold but We often lose you as a smell and often the taste of things here is different.

Question 3

what does taste transmission involve

Answer 3

• receptors (taste buds)
• cranial nerves
• nucleus solitarius (brain stem)
• thalamus
• gustatory cortex

Question 4

taste receptors

Answer 4

located on taste buds in the mouth, soft palate, pharynx and epiglottis
taste buds on the tongue embedded in the circumvallate, fungiform and foliate papillae

Question 5

circumvallate papillae

Answer 5

-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
- abrasion of posterior tongue against hard palate in mastication opens the trench - fluids containing tastants are directed to taste bud

Question 6

ducts of Von Ebner salivary glands in circumvallate papillae

Answer 6

they secrete:
- serous saliva - wash the taste buds
- lipase - begins fat digestion

Question 7

fungiform papillae

Answer 7

• mushroom-shaped papillae scattered over the anterior 2/3 of the tongue
  -each papillae contains 6-8 taste buds

Question 8

foliate papillae

Answer 8

• 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 taste buds
• mechanical motion of chewing helps direct the tastants down the folds
• fewer foliate papillae in humans compared to other species

Question 9

filiform papillae

Answer 9

• filiform most numerous of papillae - dont contain taste buds
• shape of fir tree
• allow soft substance to be licked into the mouth

Question 10

taste receptor distribution

Answer 10

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

Question 11

5 basic tastes

Answer 11

salty
sweet
sour
bitter
umami

Question 12

flavour

Answer 12

flavour is the perceived taste - information integrated with input from the multiple systems; smell, touch, temperature, nociceptive information

Question 13

taste buds

Answer 13

• goblet shaped structure
• presents a taste pore that opens into the oral cavity
• contain 50-75 cells

Question 14

cell types in the taste buds

Answer 14

gustatory cell - transmit the taste
sustentacular cell - supporting
basal cell - for regeneration

Question 15

gustatory cells

Answer 15

• 10-14 day life span
• microvilli extend from the apical end of the gustatory cell into the taste pore
• taste receptors on microvilli
• nerve fibres enter at base of taste bud and wrap around the gustatory cell

Question 16

stimulation of taste pathways - direct

Answer 16

1. chemical flows via sodium channels into the receptor cell
2. increased positive charge -> activation of voltage gated calcium channels
3. leads to calcium influx and neurotransmitter reflex
4. synapse with first order neurone

Question 17

stimulation of taste pathways - indirect pathway

Answer 17

1. chemical binds to receptor (G protein)
2. G protein releases alpha subunit
3. release of IP3
4. -> ion channel activation -> sodium influx
5. -> depolarisation of cell membrane, influx of calcium and neurotransmitter release
6. synapse with first order neurone

Question 18

taste pathway

Answer 18

1. chemical stimulation of taste bud
   - synapse between gustatory cell and 1st order neurone
2. first order neuron: facial nerve, glossopharyngeal nerve, vagus nerve
   - synapse between 1st and 2nd order neurones
3. nerve cell body of 2nd order neurone in the gustatory nucleus of brain stem
   - synapse between 2nd and 3rd order neurones
4. nerve cell body of 3rd order neurone in the ventral posterior nucleus of the thalamus
5. projects to gustatory cortex

Question 19

first order neurones

Answer 19

One of 3 cranial nerves
- Depends on where the taste receptors are will determine which cranial nerve is transmitting the information
facial - soft palate and anterior 2/3 tongue
glossopharyngeal - pharynx and posterior 1/3 tongue
vagus -epiglottis

Question 20

functional modalities of the facial nerve

Answer 20

• special visceral efferent (branchial) -> muscles of facial expression
• general visceral efferent (PNS_ - submandibular and sublingual salivary glands, lacrimal glands and nasal mucosa
• general somatic afferent (general sensation) -skin around ear
• special visceral afferent (taste) - anterior 2/3 of tongue and soft palate

Question 21

facial nerve - special visceral afferent pathway
- branch from soft palate

Answer 21

1. greater petrosal nerve - passes through pterygopalatine fossa
2. enters skull at unnamed foramen
3. joins main part of facial nerve in petrous temporal bone. sensory nerve cell body located in geniculate ganglion
4. enters cranial cavity at internal auditory meatus
5. enters brain stem as the nervus intermedium at the pons medullary junction
6. passes in tractus solitarius to terminate in the nucleus solitaries

Question 22

facial nerve - special visceral afferent pathway
- branch from tongue

Answer 22

1. chorda tympani (initially travels from tongue with the lingual nerve of V3)
2. enters skull at the petrotympanic fissure
3. joins main part of facial nerve in petrous temporal bone. sensory nerve cell body located in geniculate ganglion
4. enters cranial cavity at internal auditory meatus
5. enters brain stem as the nervus intermedium at the pons medullary junction
6. passes in tractus solitarius to terminate in the nucleus solitaries

Question 23

functional modalities of the glossopharyngeal nerve

Answer 23

• special visceral efferent (branchial) - stylopharyngeus
• general visceral efferent (PNS) - parotid gland
• general somatic afferent (general sensation) - posterior 1/3 tongue, pharynx, parts of ear
• general visceral afferent - carotid body and sinus
• special visceral afferent (taste) - posterior 1/3 of tongue and pharynx

Question 24

glossopharyngeal -special visceral afferent pathway

Answer 24

sensory nerve cell bodies located in superior and inferior glossopharyngeal ganglia
glossopharyngeal nerve enters skill at jugular foramen
- enters brain stem at the medulla
- passes in tractus solitarius to terminate in the nucleus solitarius

Question 25

vagus nerve functional modalities

Answer 25

- special visceral efferent (branchial) - muscles of pharynx and larynx - general visceral efferent (PNS) - smooth muscle of abdomen and thorax and cardiac muscle - general somatic afferent (general sensation) - larynx, parts of ear - general visceral afferent - thoracic and abdominal viscera and aortic body and sinus - special visceral afferent (taste) - epiglottis

Question 26

vagus - special visceral afferent pathway

Answer 26

sensory nerve cel bodies located in inferior vagal ganglion - enters skull at jugular foramen - enters brain stem at the medulla - passes in tractus solitarius to terminate in the nucleus solitarius

Question 27

nucleus solitarius

Answer 27

- located in the medulla - receives visceral afferent fibres from facial, glossopharyngeal and vagus nerves - taste fibres terminate in the gustatory nucleus at the rostral end

Question 28

ascending pathway

Answer 28

axons of the 2nd order neurones ascend in the ipsilateral central tegmental tract, pass through pons and midbrain to the thalamus terminate in the ventral posterior nucleus of thalamus

Question 29

ascending pathway - gustatory cortex

Answer 29

axons of the 3rd order neurone project to the gustatory cortex located in the insular cortex and operculum

Question 30

output from the gustatory cortex

Answer 30

projections from the cortex are sent to other areas for taste processing including: - limbic system - memory - orbitofrontal cortex - flavour, perception, reward value, aversion - lateral hypothalamus - controlling energy balance, regulating feeding behaviours

Question 31

where does gustatory cortex receive input from

Answer 31

limbic system, lateral hypothalamus, prefrontal cortex, olfactory areas, other regions of insular cortex

Question 32

labelled line theory of taste transmission

Answer 32

there are distinct groups of neurones in the pathway (from the receptor to the gustatory cortex) that are concerned with encoding information about a single specific taste quality

Question 33

across - neuron pattern pathway theory of taste transmission

Answer 33

groups of neurones in the pathway combine to encode multiple taste qualities

Question 34

taste perception

Answer 34

chemical tastants stimulate taste receptors - information transmitted via the nucleus solitarius in the brainstem to the thalamus and then to the gustatory cortex and association areas - psychological state: attention, emotion, expectations, memories - homeostatic signals: hunger, satiety, visceral signals