Gustation Flashcards
How does the information about taste get to the brain (in general terms)?
Oral pharynx -> taste buds on tongue, epiglotus, pharynx -> cranial nerve VII, IX, X -> brainstem = nucleus of the solitary tract (gustatory nucleus), rostral part -> ventral posterior (medial) thalamus -> Insular cortex = Primary gustatory cortex
NOTE: caudal solitary tract - “taste” from the visceral organs e.g. signaling harmful substance in the intestines
Look at a schematic image:
What other structures could get this information (and create our conscious experience of gustation)?
Insular cortext integrates more information (e.g. visceral sensory signals) -> passed on to Orbito or Medial prefrontal cortex
- it also gets input from Primary Olfactory cortex (i.e. pyriform cortex)
- creates Flavour, hedonic value of food
Describe the anatomy of the oral cavity/pharynx. What cranial nerves does it correspond to?
Along the tongue we find different types of papillae
- Posterior in esophagus = Vagus
- Posterior 1/3 = Glossopharangyal
- Anterior 2/3 = Facial
Food, water-soluable substances fall into the trenches between papillae -> interact with taste buds
How does the taste bud look like?
Molecules interact with Taste cells via the Taste pore -> release neurotransmitters -> cranial nerve
What categories of tastes do we know?
Salt, acids (sour), sweet, bitter, umami (amino acid)
How exactly does transduction for these tastes function?
Sour and salty -> interaction with ion channels -> cations enter the cell -> depolarization -> opening of voltage-gated channels of Ca2+ -> exocytosis of vesices -> release of serotonin
Sweet, bitter, umami -> g-protein-coupled receptors -> second messenger systems -> further interactions e.g. releasing from intracellular stores, depolarization -> exocytosis
- for one taste may be dimeric (two g-protein r.), heteromeric (two different g-p r.)
What can you say about topography of taste (on tongue) - which cranial nerves?
Although the tastes are not just in those specific places -> they have higher population in there
-> will determine which cranial nerves innervate it
Do taste categories have the same sensitivity? Why is that so?
No.
- Seems like bitter needs even smaller concentration (nanoMolar) to get activated than salty and sweet (miliMolar
- makes sense cause potentially harmful substances are more likely to be bitter
- while salts and other we need to ingest more of it
What kind of coding do we find here? What does it mean? Do we have a map of that in the cortex?
Frequency of firing and topographical distribution -> labeled-line coding i.e. whenever a specific axon in anterior portion it will be labelled as “sweet”
- Label present based on particular receptors
- BUT in general we tend to be more concerned with pleasure/motivation of food rather than the exact catogories - so we don’t need a map of it in the cortex
Explain the branching of trigeminal nerve in the picture.
What specific receptors can we find here?
Transient receptor potential channels (TRP)
- sensitive to heat, cold, acids, substances from the environment e.g. capsaicin
- could modulate current of the channels normally responding to heat
How does the path from these receptors up to the cortex look like?
Ganglion cells -> nerves descend down and form the spinal trigeminal tract -> synapses on second order neurons in spinal trigeminal nucleus -> crossing over -> ascending through tegmentum -> ventral posterial medial nucleus -> 3rd. n. towards cortex
Why would we need this path?
Alert us about irritation e.g. in the mouth, cornea -> brainstem activates local circuits -> triggers reflexive responses e.g. reticular formation would induce cough, sneeze, tear up
