Gustatory System Flashcards
What does the gustatory system detect?
Ingested molecules called tastants
What is flavor?
Combination of olfactory, taste, and somatosensory cues.
What are taste buds?
- Epithelial specializations
- Contain taste pores
- located primarily on surface of tongue in papillae
- Found on the palate, pharyn, larynx, and upper esophagus
What are taste pores and where are they located?
- Fluid filled constriction on apical end of taste bud
What are the 3 types of papillae?
- Fungiform
- Circumvallate
- Foliate
What are fungiform papillae?
- Mushroom shaped structures on the anterior 2/3rds of dorsal aspect of tongue
- Contain 1-5 taste buds in each one
What are circumvallate papillae?
- 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
What are foliate papillae?
- appear as a series of parallel clefts on the lateral margin of the tongue
- around 600 taste buds in the cleft walls
What are the components of the taste buds?
- Taste Receptor Cells
- Supporting Cells
- Basal Cells
Describe the structure of the taste receptor cells.
- Elongate epithelial cells that go from one end of the taste pore to the other
- Apical end
- Basal end
Describe the apical end of the taste receptor cells
Covered with microvilli that project into a taste pore.
-Microvilli contain receptors for tastant molecules
Describe the basal ends of the taste receptor cells
Form chemical synapse-like connections with sensory neurons
What is the function of the taste receptor cells?
Gustatory transduction
What is the life span of the taste receptor cells?
10-14 days
What are the supporting cells in the gustatory system?
Elongated epithelial cells located adjacent to the taste receptor cells
Describe the basal cells in the gustatory system.
Stem cells located at the base of the taste bud
- give rise to taste receptor cells
What does the gustatory system distinguish?
5 stimulus qualities:
- salty
- sour
- sweet
- bitter
- umami
What are the steps of gustatory transduction?
- Tastants diffuse through fluid of taste pore
- Salt and sour stimuli flow into the cell through selective and non selective ion channels.
- Sour and bitter stimuli block K+ ion channels ( increasing amount in cell)
- Sweet, bitter, and umami bind to metabotropic receptors. Either close K+ channels, open Ca++ channels, release Ca++ from stores.
- Depolarization activates Na+ channels
- More Depolarization opens Ca++ channels in the basal end, allowing Ca++ to flow into the cell causing release of neurotransmitter.
Where are the cell bodies of the taste receptor cells (afferent) located?
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
What is the distribution of the taste receptor cells?
Terminate on numerous taste buds
-Each taste bud has several taste receptor cells
Explain how special visceral afferent neurons encode for different taste stimuli
- 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.
What is the pathway of information in the gustatory system?
- Central projections of CN 7, 9, 10–> Nucleus of Solitary Tract–> Primary Taste Cortex–> Orbitofrontal Cortex
Where do the fibers of CN 7, 9, and 10 project to?
Rostral regions of the ipsilateral nucleus of the solitary tract in the medulla
Where is the nucleus of the solitary tract?
Medulla
How is the nucleus of the solitary tract divided?
Rostral (gustatory) and Caudal (visceral) Nuclei
Where do the axons of the gustatory nucleus project to?
- Visceral nucleus
- Amygdaloid, hypothalamus, ventral posterior medial nucleus (thalamus), and primary taste cortex.
What are visceral nucleus projections involved in?
Gustatory- Visceral reflexes that influence salivary secretion, mimetic responses, and swallowing.
What are amygdaloid and hypothalamus projectiosn involved with?
Feeding behavior
Where do the ventral posterior medial nucleus (thalamus) projections terminate?
Primary taste cortex
What is the structure and function of the primary taste cortex?
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
What is the role of the orbitofrontal cortex in the gustatory system?
- Receives input from the primary taste cortex
- Site of integration for taste, olfactory, and visual cues associated with the ingestion of food
What is unique about the pathway of information in the gustatory system?
Information is projected to the IPSILATERAL side
What are disorders of taste called?
- Ageusia (absence)
- Hypogeusia (decreased)
- Hypergeusia (increased)
- Dysgeusia (distortion)
