OE L31 Biology of Taste Flashcards
What are the 5 taste sensations?
- Salty (supplies vital minerals lost through sweat and urine)
- Sweet (glucose for energy)
- Sour (stimulates salivation, maintains pH)
- Bitter (avoid toxic intake)
- Umami (protein)
Where are taste buds found?
The majority are found on the foliate, fungiform and circumvallate papillae.
Some found in the soft palate, epiglottis and oesophagus.
Where are the taste buds found on papillae?
Found on the lateral borders of the papillae.
What is the basic composition of taste buds?
- Each taste bud contains 50-100 taste cells (type of neuronal epithelial cell)
- Taste pore superiorly
- Afferent nerves inferiorly (send taste info to CNS)
- Type I, II and III taste cells extend into the taste pore
- Type IV taste cells are basal, less defined progenitor cells that develop into the 3 other cell types, do not extend into the pore
Describe type I taste cells.
- Aka dark cells
- Narrow dense cell neck
- Tubular elements and granular appearance
- 40 microvilli on flattened surface
- They secrete the substance found in the pore/pit (rich in GAGs, enzymes and vit C)
Describe type II and III taste cells.
- Aka light cells
- Type II are directly involved in taste transduction and have a thick microvillus which porjects into the taste pore
- Type II also contain synaptic vesicles which synapse with adjacent nerve fibres
- Type III do not have microvilli
Describe the nerve fibres found in taste cells.
- Nerve fibres lose their myelin sheats when they enter the taste bud
- Fibres invaginate into type I cells, coil around type II cells and form synaptic connection with type III cells
- They don’t have a specific, defined position in the taste bud
What is the life span of taste cells?
14-30 days (short)
Outline how taste cells detect soluble chemical substances.
- Taste cells are electrically excitable cells, capable of generating an action potential
- Taste cells have voltage dependant channels for sodium, potassium and calcium
Describe how we taste salt.
Salt:
- Amiloride-sensitive sodium channel is the salt receptor
- Influx of sodium ions depolarises taste cells, generates AP
- Amiloride can block the sodium channel to prevent salty taste sensation
Describe how we taste sourness.
Sour:
2 mechanisms-
1) Sourness is a measurement of proton (H+) concentration. Protons block Na and K channels thus causing taste cell repolarisation
2) Otop1 proton channel and PKDL channel acts as receptors for sourness
Describe how we taste sweetness.
Sweet:
- GPCRs act as sweet receptors
- Causes taste cell depolarisation by using cyclic AMP to block a basolateral potassium channel
Describe how we taste bitterness.
Bitter:
2 mechanisms-
1) Internal calcium release from mitochondrion of taste cells causes neuron-transmitter deportation
2) cAMP phosphodiesterase (PDE) decreases intracellular cAMP, causes an open potassium channel, leads to hyperpolarisation
Describe how we taste umami.
Umami:
- GPCRs (T1R1 and T1R3) form a receptor for glutamate (AA)
- Activation of these receptors decreases cAMP causing repolarisation/hyperpolarisatoin of taste cells
What factors affect taste perception?
- Everybody has specific food and drink preferences as we all have our own thresholds for cell depolarisation
- Oral cavity temperature: cold food and drink reduces receptor ability
- Combining tastes changes our perception
- Hormonal and cytokine influences alter taste thresholds
- Age: sensitivity decreases with age
- Genes: 30% of caucasians are insensitive to bitter tastes
