Taste (gustation) Flashcards
LO
- Be able to describe the specialized sense organs involved in gustation at a molecular and cellular level
- Be able to describe how gustatory information can be coded
- Be able to describe the structures of the brain that processes this type of sensory information in the CNS
Tell me about the surface of the tongue
- The sense organ: the tongue. The surface of the tongue has specialised invaginations called taste papillae
- Each Fungiform has ~3 taste buds on the apical surface
- Each Circumvallate has ~250 taste buds in the trench
- Folliate are organized into parallel ridges with ~600 taste buds
Tell me what happens when food is taken into the mouth
- When food is taken in it is dissolved into the saliva – the papillae concentrate the dissolved chemicals in the region of the taste buds
- Taste buds contain the sensory receptors cells
What do chemicals stimulate?
Followed by what and towards what location?
Chemicals stimulate fungiform papillae, followed by foliate and circumvallate towards the base of the tongue
What are the 5 basic tastes
Give an example of each?
Tell me about how different tastes are distinguished between?
Taste buds are able to distinguish between different tastes through detecting interaction with different molecules or ions. Sweet, savouriness, and bitter tastes are triggered by the binding of molecules to G protein-coupled receptors on the cell membranes of taste buds.
How many specialised epithelial cells can a single taste bud contain?
A single taste bud can contain up to 50 specialised epithelial cells = taste cells
What do the tips of taste cells have and why are they there?
- The tips of the cells have microvilli – increases surface area, come together at the taste pore – concentrates chemicals onto receptor proteins
- Taste receptor proteins located in microvilli
- Regeneration (Basal cells)
What are the 2 key domains in the taste cell?
2 key domains – apical (external environment) & basolateral (taste bud)
Apical microvili contain receptor proteins, what are these and what tastes do they detect?
- ion channels: salt & sour/acids
- GPCR: sweet, bitter, umami
What does the basolateral surface of taste cells contain?
Basolateral surface contains ion channels and cellular machinery required to release neurotransmitter
What do taste cells synapse onto?
Synapse onto cranial nerves (the facial (VII), glossopharyngeal (IX), and vagus (X))
What are the neurotransmitters of taste cells?
serotonin and ATP
Tell me the stages to salt and sour sensing via ion channels
Tell me about T1Rs and sweet and umami
- T1Rs can form heterodimers
- The ligands that the T1Rs bind to varies depending on the combination
- Different T1R heterodimers encode sweet and umami
Tell me about taste blindness: bitter?
- 25% of the population
- Inability to sense phenylthiocarbamide (PTC)
- The gene responsible was identified as the T2R receptor gene encodes a GPCR
- T2Rs are not present in taste cells that express T1R subtypes (sweet and umami)
Bitter
- There are many T2R subtypes that recognize different combinations of ligands
- Sequence diversity enables the detection of many different bitter compounds
What are the downstream signalling molecules?
Tell me about the sweet signalling pathway
And give examples of natural sugars
Tell me about Umami signalling pathway
Name some food with associated high protein
Tell me about the bitter signalling pathway and give an example of a taste
Summary: features of gustatory transduction
- Taste receptor proteins are concentrated in the microvilli of taste cells
- Ion channels signal salt and sour
- GPCRs signal sweet, amino acid and bitter
- GPCRs signal through a PLCB2, TRPM5 pathway
- Graded receptor potentials spread to the basal domain
- Voltage-gated channels mediate release neurotransmitter onto the terminals of sensory afferents
Summary of the key taste receptors
- Amiloride sensitive Na channel, Transient Receptor Potential (TRP), metabotropic glutamate receptor (mGluR), T2R and T1R subtypes.
Tell me about the central processing of gustation and the cranial nerves involved
- Cranial nerve VII: facial nerve and Chorda Tympani (projects back from tongue and palate)
- Cranial nerve IX: lingual branch of the glossopharyngeal nerve (project from back of tongue, epiglottis)
- Cranial nerve X: superior laryngeal branch of the vagus nerve (projects back from oesophagus)
- Cranial nerves have a topographical organization in the gustatory nucleus
- Cranial nerve VII – rostral/Cranial nerve IX – mid-region/Cranial nerve X – caudal
- The nucleus of the solitary tract facilitates the integration of sensory information about taste and visceral sensory information
Central processing of gustation
Mapping of gustatory cues in the insular cortex
- A cartoon of the representation of tastants in the insular cortex developed by mapping responses in the insular cortex to tastants:
- Active cells are in red. In the region of analysis there is a large response to NaCl, but not bitter and sweet tastants in the same region (i.e., fewer red dots)
- Provides supportive evidence for a gustatory map in the insular cortex
Taste is conveyed to the CNS using labelling line coding
- In the T2R rescue mice, PLCB2 has been ‘knocked in’ to PLCB2 knockout genetic background and selectively rescued back in T2R cells
- What does this experiment tell us about the type of coding in the periphery?
Central processing of gustation
Taste information is relayed via what?
Taste information is relayed, via the thalamus, to cortical structures (different to olfaction!)
What does orbitofrontal cortex give and what is it thought to be involved in?
- Orbitofrontal cortex gives us our perception of food
- Orbitofrontal cortex is thought to be involved in signaling satiety
Central processing of gustation
- Two- way transfer of information between the nucleus of the solitary tract and the hypothalamus and amygdala
- Hypothalamus – homeostatic responses > feeding behaviour
- Amygdala – limbic system. Affective response to food – pleasurable or repulsive experience of food, food seeking behaviours
General summary: chemosensation
- Gustation and olfaction are mediated by specific gustatory and olfactory receptors. Both receptors have a high turn-over.
- Signal transduction in gustatory receptors involves both ion channels and GPCRs, whilst odorant receptors are a large family of GPCRs
- Gustatory receptors respond to a more limited range of stimuli than olfactory receptors and typically have a much lower sensitivity
