Chemosenses Flashcards
What is the task of chemoreceptors that for gustation and olfaction?
To detect environmental chemicals
What is flavour?
The blending of taste and smell
What is umami?
the savoury taste of the amino acid glutamate
What are the 5 organs of taste?
True/false: The tongue can only taste specific things like sweetness, saltyness etc. in highly specific areas of the muscle.
False - the whole tongue is capable of tasting all 5 tastes. There are however areas of sensitivity, that are better equipped to detect only specific tastes.
What is the relationship between papillae, taste buds, and taste cells?
Each papilla has 1 - 100s of taste buds
Each taste bud has 50 - 150 taste cells
What are the 4 types of taste receptor cells in the tongue?
Glia
Ion channels
GPCRs
Basal cells (progenitor cells able to replenish taste cells should they become damaged)
Describe how the concentration of the taste stimulus (tastant) affects a person’s ability to taste.
- The […] is the chemically sensitive part of a taste receptor. This end has […] that project into the taste pore.
- A taste receptor is not a neuron, but it does synapse with […] and form […] synapses with basal cells.
- Apical end; microvilli
- Gustatory afferent axons; electrical and chemical
How long is the lifespan of a taste receptor cell?
2 weeks
Describe how taste receptor cells are activated.
When activated, membrane depolarizes. If this is large enough (threshold) the taste cell may fire action potentials. Depolarization of membrane causes voltage gated Ca2+ channels to open; Ca2+ enters cytoplasm, causes trafficking of NTs to synapse (serotonin and NE)
If we only have 5 types of taste stimuli that we can respond to, how do we get such complex distinction of flavor in our foods?
Combinatorial diversity - cells that detect different stimuli talk to one another and send the combination of that information up to the nucleus solitarius which then allows us to know we’re tasking a bananna vs. garlic mashed potatoes.
For the following tastants, describe the receptors they interact with to transduce a signal in a taste cell:
- Salt
- Sour
- Sweet
- Bitter
- Umami
- Salt and sour = ion channels
- Sweet, bitter and umami = GPCRs
Describe the mechanism by which we taste saltiness.
Describe the mechanism by which we taste sourness.
Describe the mechanism by which we taste bitterness.
Bitter receptors are poison receptors.
Describe the mechanism by which we taste sweetness.
The chemical signaling pathway is exactly the same as it is for bitterness, but it uses a different receptor from the same GPCR family.
Describe the mechanism by which we taste umami.
The chemical signaling pathway is exactly the same as it is for bitterness, but it uses a different receptor from the same GPCR family.
If sweetness and bitterness are transduced by the same signaling pathway, why don’t we confuse these tastes?
Because bitter receptors and sweet receptors are expressed in different taste cells and connect to different axons
Describe the central taste pathway once taste stimuli have been transduced by the taste cells in the body.
What is the organ of smell?
A small thin sheet of cells high up in the nasal cavity called the olfactory epithelium
What are the 3 main cell types in the olfactory epithelium?
How long do olfactory receptors live for?
4 weeks
What is the role of mucus in smelling?
What is its composition?
- Odorants need to dissolve in solution before they can be smelled. Mucus is the substance they dissolve in for us to smell them.
- Made of water base with mucopolysaccharides, antibodies, enzymes, proteins and salt
What are pheromones?
Are olfactory receptor cells just receptors or are they neural cells?
Unlike hearing and taste, olfactory receptors are neurons with dendrites that project into olfactory epithelium and have receptors on them for the odorants.
Describe the signaling pathway that occurs from odorant to depolarization.
If the resulting depolarization is large enouch, it will exceed threshold for AP in cell body and spikes will propogate out along axon into CNS.
How does a response to an oderant terminate?
Oderant diffuses away
Enzymes break it down
cAMP activates other pathways that end transduction
Each olfactory bulb lies on the […] of the […] bone.
Cribiform plate
Ethmoid
Describe the microstructure of the neural connections between the cribiform plate and the olfactory bulb.
Single unmyelinated olfactory receptor neurons pass from olfactory epithelium, through cribiform plate, into olfactory bulb where they form a group of axons with other receptor neurons, called a glomerulus. That glomerulus then synapses with a second order olfactory neuron that has many dendritic projections to talk to all those axons. Each golmerulus receives input from only one type of receptor cell.
Describe the full central pathway of signal transduction from odorant to olfactory cortex.
