*L07 - Taste and smell Flashcards
What are the advantages of being able to taste and smell?
To potentially stop you eating things that are bad for you
What are the 5 basic tastes that can be detected?
Sweet, sour, bitter, salt, umami
Where are the taste cells?
They are present in the tongue and palate so can taste without a tongue but not very well. The tongue has areas that are more sensitive to certain tastes e.g. sweet area etc. However these areas are not exclusive, sweet can be detected in non sweet areas just not as strongly.
How is taste converted to action potentials?
Taste cells detect tastes and pass them on to neurones through neurotransmitter release. They are not sensory neurones even though their connection with sensory neurones looks like a synapse.
How often are taste buds replaced and how does this occur?
They are replaced roughly every 2 weeks as they are worn away by food. They are replcaed by basal cells which grow into taste buds
What is the mechanism behind the conversion of taste to an action potential?
The chemical binds to the taste bud which causes a transduction of the signal causing a change in the potential of the receptor. This causes depolarisation that causes opening of calcium channels and an influx of Ca2+ ions. This causes release of vesicles of the neurotransmitter to the sensory neurone.
What is the mechanism for detection of salt?
Open salt channels allow salt entry and depolarisation.
What is the mechanism for detection of sour?
To do this must detect H+ ions. H+ ions cause blockage of K+ channels which causes depolarisation. H+ can also enter the cells by TRP (transient receptor potential) channels.
How are sweet, umami and bitter tastes detected?
Through a combination of GPCR which lead to increases in Ca2+ and hence neurotransmitter release.
What are the combinations of GPCRs for different tastes?
Different combinations of T1R and T2R GPCRs for the sweet, umami and bitter tastes. Sweet is T1R2 and T1R3, umami is T1R1 and T1R3 and T2R.
What is the pathway of neurones for detecting taste?
Primary neurones from the tongue synapse in the primary gustatory nucleus in the medulla oblongata. Secondary neurones then synapse in the VPM nucleus of the thalamus. Tertiary neurones then synpase in the tertiary gustatory cortex.
What does the neural coding of taste mean?
It means that all of the inputs from the tongue are compared so a lesion can change the way we taste things.
Where are the two secondary pathways of the taste neurones?
One is to the medulla for saliva production etc.
One is to the hypothalamus for how the food makes us feel e.g. palatability.
What are the main detectors of smell in the nasal cavity?
The olfactory receptor cells which are neurones with cilia in the nasal cavity.
How often are the olfactory receptor cells replaced? How does this occur?
Every 4-8 weeks, neurones are made in the lateral ventricle and then migrate.
