Gustatory System

Question 1

What does the gustatory system detect?

Answer 1

Ingested molecules called tastants

Question 2

What is flavor?

Answer 2

Combination of olfactory, taste, and somatosensory cues.

Question 3

What are taste buds?

Answer 3

• Epithelial specializations
• Contain taste pores
• located primarily on surface of tongue in papillae
• Found on the palate, pharyn, larynx, and upper esophagus

Question 4

What are taste pores and where are they located?

Answer 4

• Fluid filled constriction on apical end of taste bud

Question 5

What are the 3 types of papillae?

Answer 5

1. Fungiform
2. Circumvallate
3. Foliate

Question 6

What are fungiform papillae?

Answer 6

• Mushroom shaped structures on the anterior 2/3rds of dorsal aspect of tongue
• Contain 1-5 taste buds in each one

Question 7

What are circumvallate papillae?

Answer 7

• Central bulges surrounded by circular trenches arranged in a chevron located at the rear of the tongue
• around 250 taste buds along their trench walls

Question 8

What are foliate papillae?

Answer 8

• appear as a series of parallel clefts on the lateral margin of the tongue
• around 600 taste buds in the cleft walls

Question 9

What are the components of the taste buds?

Answer 9

1. Taste Receptor Cells
2. Supporting Cells
3. Basal Cells

Question 10

Describe the structure of the taste receptor cells.

Answer 10

• Elongate epithelial cells that go from one end of the taste pore to the other
• Apical end
• Basal end

Question 11

Describe the apical end of the taste receptor cells

Answer 11

Covered with microvilli that project into a taste pore.

-Microvilli contain receptors for tastant molecules

Question 12

Describe the basal ends of the taste receptor cells

Answer 12

Form chemical synapse-like connections with sensory neurons

Question 13

What is the function of the taste receptor cells?

Answer 13

Gustatory transduction

Question 14

What is the life span of the taste receptor cells?

Answer 14

10-14 days

Question 15

What are the supporting cells in the gustatory system?

Answer 15

Elongated epithelial cells located adjacent to the taste receptor cells

Question 16

Describe the basal cells in the gustatory system.

Answer 16

Stem cells located at the base of the taste bud

- give rise to taste receptor cells

Question 17

What does the gustatory system distinguish?

Answer 17

5 stimulus qualities:

1. salty
2. sour
3. sweet
4. bitter
5. umami

Question 18

What are the steps of gustatory transduction?

Answer 18

1. Tastants diffuse through fluid of taste pore
2. Salt and sour stimuli flow into the cell through selective and non selective ion channels.
3. Sour and bitter stimuli block K+ ion channels ( increasing amount in cell)
4. Sweet, bitter, and umami bind to metabotropic receptors. Either close K+ channels, open Ca++ channels, release Ca++ from stores.
5. Depolarization activates Na+ channels
6. More Depolarization opens Ca++ channels in the basal end, allowing Ca++ to flow into the cell causing release of neurotransmitter.

Question 19

Where are the cell bodies of the taste receptor cells (afferent) located?

Answer 19

Geniculate ganglion of facial nerve= anterior 2/3
Petrosal ganglion of CN 9= Posterior 1/3
Nodose Ganglion of CN 10= Epiglottis and Upper Esophagus

Question 20

What is the distribution of the taste receptor cells?

Answer 20

Terminate on numerous taste buds

-Each taste bud has several taste receptor cells

Question 21

Explain how special visceral afferent neurons encode for different taste stimuli

Answer 21

• Each sensory neuron receives input from a population of taste cells with a distinctive set of response specificity.
• Different tastes are encoded by different patterns of activity
• This occurs in the entire fiber population or by the activation of different, but overlapping, sets of fibers.

Question 22

What is the pathway of information in the gustatory system?

Answer 22

1. Central projections of CN 7, 9, 10–> Nucleus of Solitary Tract–> Primary Taste Cortex–> Orbitofrontal Cortex

Question 23

Where do the fibers of CN 7, 9, and 10 project to?

Answer 23

Rostral regions of the ipsilateral nucleus of the solitary tract in the medulla

Question 24

Where is the nucleus of the solitary tract?

Answer 24

Medulla

Question 25

How is the nucleus of the solitary tract divided?

Answer 25

Rostral (gustatory) and Caudal (visceral) Nuclei

Question 26

Where do the axons of the gustatory nucleus project to?

Answer 26

• Visceral nucleus

- Amygdaloid, hypothalamus, ventral posterior medial nucleus (thalamus), and primary taste cortex.

Question 27

What are visceral nucleus projections involved in?

Answer 27

Gustatory- Visceral reflexes that influence salivary secretion, mimetic responses, and swallowing.

Question 28

What are amygdaloid and hypothalamus projectiosn involved with?

Answer 28

Feeding behavior

Question 29

Where do the ventral posterior medial nucleus (thalamus) projections terminate?

Answer 29

Primary taste cortex

Question 30

What is the structure and function of the primary taste cortex?

Answer 30

S: Located in the anterior insula of the temporal lobe and the operculum of the frontal lobe
F: responsible for perception and discrimination of taste stimuli

Question 31

What is the role of the orbitofrontal cortex in the gustatory system?

Answer 31

• Receives input from the primary taste cortex

- Site of integration for taste, olfactory, and visual cues associated with the ingestion of food

Question 32

What is unique about the pathway of information in the gustatory system?

Answer 32

Information is projected to the IPSILATERAL side

Question 33

What are disorders of taste called?

Answer 33

• Ageusia (absence)
• Hypogeusia (decreased)
• Hypergeusia (increased)
• Dysgeusia (distortion)