Lecture 16 Flashcards
What are the functions of the chemical senses?
Identify food sources
Avoid noxious substances
Find a mate or make territories
How are chemical senses achieved?
By the gustatory system and the olfactory system
- Have separate transduction mechanisms
- Information is processed in parallel
- Information is merged in the CNS
What are the five basic tastes?
Salty
- vital electrodes, ionotropic
Sour
- acids, H, ionotropic (fatty acids etc)
Sweet
- innate fondness, high energy foods, metabotropic (GPCRs)
Bitter
- instinctively rejected, often poisons, metabotropic
Umami
- savory taste of glutamate, metabotropic
How do we perceive all of the flavors of food?
Likely other tastes and receptors e.g. fat, starch
Deficits in nutrients can lead to cravings
Combination of taste, smell and touch (texture) are combined in the cortex
What is the function of the Lingual papillae?
Taste-sensing structure
Taste organs = primarily tongue, also cheeks, soft palate, pharynx, epiglottis
What are the four types of lingual papillae?
Filiform
- spiked, no taste buds, sense texture, most abundant
Foliate
- ridges, least abundant, gone by 2-3 years
Fungiform
- mushrooms, mainly at sides and front
Circumvallate
- pimples, large, contain about half of all taste buds
What do taste buds contain?
Taste cells and gustatory afferents
How many taste buds are there in total?
2000-5000
- Different range of sensitivity may depend on number of taste buds in individual
How many taste cells are there per taste bud?
100
What is the function of taste pores?
Stimulus detection by microvilli
What type of receptors are taste cells?
chemoreceptors
What do gustatory afferents do?
Carry information to CNS
What type of tastes are GPCRs used for?
Bitterness, sweetness and umami
- similar transduction mechanism to other cells
What is TrpM5?
Ion channel opens to allow other cations in cell (Na, Ca)
What is VGNC?
Causes second depolarization (depolarization size depends on stimulus size)
Do GPCRs for taste use synaptic vesicles?
no
What activates GPCRs at the end?
Na
What is used as a neurotransmitter for GPCRs for taste?
ATP
- activates neurons
What are VGNC activated by?
Activated for sourness (alongside VGCC)
- more like a traditional synapse
- activates synaptic vesicles
- variety of neurotransmitters
Do taste cells have the same thresholds for different basic tastes?
No; they are different
How does a taste cell respond to different tastes?
e.g. can respond to sweet and salty stimuli but will respond best to one of these stimuli, as it will be detected at a lower threshold
Why can we not have a completely specific labelled line code?
Because every flavor would need a specific taste receptor (we don’t have enough proteins for that, so we need to combine the responses of many gustatory afferents using population coding)
Where do the gustatory afferents from anterior 2/3 of the tongue carry signals?
Facial nerve (cranial nerve VII)
What is the site of odorant detection?
Olfactory epithelium
How are odorants detected?
Detected as low as a few parts per trillion
Must dissolve in the mucus layer to reach olfactory receptor cells
How big is the human olfactory epithelium compared to the dog olfactory epithelium?
Human: 10cm2
Dog: 170 cm2
Dogs have 100 times more receptors per cm2
What type of neurons are olfactory receptor cells?
Chemoreceptive neurons
Where is transduction machinery found within?
Cilia at the end of the dendrite
What is the primary afferent neuron?
the axon of the olfactory receptor cell
What is the structure of axons of the olfactory receptor cell?
Thin, unmyelinated and form the olfactory nerve (cranial nerve I)
What are one of the few types of neurons that are regularly replaced in adults?
Olfactory receptor cells
How many odorant receptor proteins are there in humans?
350
What type of receptors are odorant receptor proteins?
GPCRs
Does every odorant receptor protein use the same downstream pathway?
Yes
How much of the genome do odorant receptor protein genes comprise?
3-5%
What type of mice are anosmic (cannot smell)?
Golf knockout mouse
What opens cyclic nucleotide channel to let in Na and Ca for depolarization?
cAMP
What is the function of ANO2?
Allows Cl into and out of the cell
- Cl must move out of the cell and not in like other cells
- cilia already have a higher concentration of Cl already so Cl moves down concentration
What can large enough receptor potentials lead to?
Reach threshold for action potential firing
What can an intense stimulus lead to?
Large receptor potential = increased action potential firing rate
Where does the glomeruli of the olfactory bulb input from?
Specific olfactory receptor cells
- each glomeruli is associated with a certain type of receptor cell
- second order neurons carry information from glomeruli to various regions of the brain
