6.5 Physiology of Smell, Taste and Salivation Flashcards
Describe an experimental technique to investigate smell or taste
Asking a group of people to report their senses. When investigating, you can be testing people for detection (do you smell/taste anything), thresholds (what concentration can you detect), characteristics (nice or not…), identification (can you recognise it). However, this approach is objective and people have different views as well as different sensory levels
Describe some molecular biology approaches to investigating smell or taste perception
Identifying the receptor protein or the gene coding for it, genome wide association studies can be used
Why is the number of receptors not the only reason for difference in sensory performance between species.
Not all of the genes for the receptors will be activated, there is currently no model that can predict olfactory perception from receptor activity patterns
What are some other factors that affect olfactory perception levels
-the area size of the olfactory epithelium ( ~170 cm2 in dogs, ~10 cm2 in humans)
-gas flow patterns over the epithelium (air flow continuously ‘in’ in dogs, see nasal slits)
-other smell organs (e.g dogs also have the vomerosnasal organ)
-volume of CNS in the olfactory bulb for central processing (2% of dog’s brain, 0.03% of human brain)
-the capacity to learn how to interpret smells
What is the main difference between smell and taste pathways
In the smell pathway, the neurone senses directly but in the taste pathway, an additional epithelial cell is used to sense which then sends a signal to the neurone to initiate transduction
Describe the human smell pathway
In the human smell pathway, there is an unusual layout, there is not just the primary neurone and chain to the cortex. The chain is the olfactory neurone > olfactory glomerulus > 2nd order neurones > olfactory nerve (CN I) > the olfactory bulb (*).
Describe the mechanism of transduction of smell.
Odorant binds to GPCR, cAMP then triggers depolarisation.
What is an advantage of a G protein coupled receptor for sensory detection.
The number of odorant molecules needed to trigger the G protein receptor is very low (in some cases 1), this is an advantage of the G protein receptors as they can detect the odorants even at low levels.
What are the 5 tastes
bitter, salt, sweet, sour and umami (traditionally there were only 4 before umami was discovered)
Describe the structure of taste buds
The taste sensation is caused by the depolarisation of the taste cells by different mechanisms. Taste buds contain lots of taste cells and are present in circumvalate, fungiform and foliate papillae as well as the soft palate. The middle of the tongue has less taste buds than the edges
On traditional taste bud maps, there is no specific area for umami taste buds, what is the current belief behind umami taste sensation
It is believed that the umami taste sensation is caused by glutamate (e.g in MSG) binding to the ‘savoury’ taste receptors
Describe some tasting variations in the population
Supertasters - those who have an increased bitterness perception and are very sensitive to 6-n-propylthiouracil - a chemical that gives rise to a bitter taste, those who have the gene TAS2R38 activated more have this increased perception
Boar taint, the offensive odor or taste in male pig meat to some people
What is the taste transduction mechanisms for sour and salty tastes
The receptor ion channels (TRPP3 channels for sour and ENaC channels for salty) are activated. This allows an Na+ influx to depolarise the cell.
What is the taste transduction mechanisms for sweet, bitter or umami tastes
-receptors bind to GPCRs with PIP2 or IP3 as their secondary messengers
-causes intracellular Ca increases though release from endoplasmic reticulum and membrane channels opening TRPM5 channels open to allow Na+ entry
-Na influx depolarises cell
