Chemical Senses Flashcards
Taste buds are found on which 3 of 4 types of Papillae?
- Fungiform (small bumps in middle and anterior tongue)
- Foliate (epithelial folds on lateral edges at back)
- Circumvallate (back of tongue)
What is the taste bud replacement cycle?
10 day cell cycle replaced by basal cell mitosis
Describe type 2 taste receptor cells
- Activated by Sweet, umami or butter (molecules rather than ions)
- G-coupled transduction mechanism
What receptor proteins respond to which tasteants
Bitter = T2R
Umami = T1R1 + T1R3 (dimer)
Sugar = T1R2 + T1R3 (dimer)
Dimers form large extracelluar domains in Venus fly trap arrangement
Describe transduction on type 3 taste receptors
- Ionic stimuli detected by ion channels
- Changes in channel gating directly depolarised cell
- Causes release of 5-HT onto gustatory nerve afferent
Describe how Na+ and H+ ions are transduced
Na+
- direct influx of Na+ channels down electrochemical gradient via sodium channel (directly depolarises cell)
H+ (sour)
- H+ ions flow in though channels
- although mainly intracellular acidification
- this closes H+ gated K+ channels causing depolarisation
How specific is our odour recognition
We can learn: if the difference between two similar odours is not important we can generalise into one smell
Where are olfactory sensory neurones located
In the olfactory epithelium in the nasal cavity
How is intensity of odour coded
More intense stimuli generate higher frequency of APe
Describe the transduction mechanism for olfactory sensory neurones
- Odourants bind to 7-tm domain G coupled protein receptor
- causes dissociation of G-protein
- Alpha subunit then activates adenalase cyclase causing the generation of cyclicAMP
- Directly opens a cyclic nucleotide gated non-selective cation channel
- Causes AP
