Chemical Senses 1 (Taste) Flashcards
These differ for each taste
Threshold levels needed for response
Gustatory nucleus neurons communicate with the VPM of the thalamus which projects here
Primary gustatory cortex
The two mechanisms for salt detection
Amiloride sensitive and amiloride insensitive
This inhibits sweet sensitivity
Leptin
These tests sweeter than sucrose (table sugar)
Proteins, aspartame
Many animals systems (cats, fish, salamanders, mice, and rats) were used to study this
Taste
These synapse onto basal cells via electrical and chemical synapses
Taste receptor cells
These enhance sweet sensitivity
Endocannabinoids
These are mostly sensitive to one taste
Taste cells
These are thought to be stem cells to replace taste cells
Basal cells
Neurons that send taste info to the brain
Gustatory afferent neurons (sensory)
Low salt (10-150 mM) tastes this way
Good
What tastes do we like/dislike?
Like sweet, dislike bitter
Just like sweet and bitter, this activates a second messenger system (GPCR)
Umami
Mutations in this affects the vestibular system
OTOP1
These affect the taste of salts in the amiloride insensitive mechanism
Anions
These neurons penetrate taste buds
Sensory gustatory neurons
These lead to the medulla, thalamus, and cortex
Gustatory axons
This is released in salt detection
5HT
Some taste cells only express bitter receptors and have some communication to these
Gustatory axons
Has a low pH and type III presynaptic cells respond to it
Sour
In type II cells, sweet, bitter, and umami tastants do this
Active second messenger systems which interact with ion channels and lead to NT release
This declines with age
Gustatory sensitivity
What are taste receptors likely doing all over the body?
Gathering info about some sugar produced by a bacteria or something that shouldn’t be there
What are the 5 tastes?
Sweet, salt, bitter, sour. umami
These stick out from the taste receptor cell into the taste pore to be exposed to tastants
Microvilli
Taste sour bc of proton detection
Acids
This taste uses T1R1+T1R3 receptors (type II)
Umami
These detect many molecules and structures
Taste receptors
Detect environment, signals integrated in orbitofrontal and other cortical areas
Taste (gustation) and smell (olfaction)
When are labeled lines and population coding seen in neural coding of taste?
Labeled lines at the beginning with taste cells and axons being specific to one but pop coding seen later in the cortex
This is both salty and bitter
K
Sweet receptors
T1R3
Channels are open all the time to depolarize the cell during this taste detection
Salt
Most taste reception is here
Tongue
Influences many feeding behaviors (vomiting, swallowing, digestion, breathing), mediated by other areas of the brain such as the medulla and hypothalamus
Taste info
How many taste buds are there on average? Whats the range?
2000-5000 avg. 500-20000 range
How often is taste cell sensitivity to one of the five tastes replaced?
Every 10-14 days
Rich in proteins/amino acids. Delicious, MSG or glutamate, nucleotides
Umami
How do the thresholds for salt/sweet compare to those for bitter (how do the sensitivities compare)?
High threshold for salt/sweet, low for bitter. (Bitter is in uM while salt/sweet is in mM)
Uses a combination of labeled lines (one responds to one) and population coding (one responds to many, many respond to one)
Taste neural coding
Many poisons are this taste
Bitter
Taste bud cells that are close to gustatory afferents but have no synapses or synaptic vesicles, no VG calcium channels
Type II
At least 30 of these genes are used to recognize bitter, depends on the species/person
T2R
Many areas of the tongue are sensitive to these
All basic tastes
These are important for hunger, emotion, sex, and memory
Chemical senses
Signal mechanisms can be influenced by these to do things like enhance or inhibit sweet sensitivity
Signals like leptin and endocannabinoids
These open with low pH and are H permeable
OTOP1
Taste bud cells that use GPCRs
Type II
Bitter receptors
T2R
We crave these when they are lacking
Nutrients
In type II cells, salt and sour tastants pass through these
Ion channels
Good markers for sour sensitive cells
PKD2L1 and OTOP1
The more important sour sensing receptor
OTOP1
The heteromeric dimers that make up umami receptors that detect some umami tastants
T1R1+T1R3
Some of these cells also synapse onto taste receptor cells
Basal cells
This is selectively expressed in a unique pop of taste bud cells (type III)
OTOP1
These are found in the stomach and intestine
Gustducin and T1R3 receptors (sweet)
The oldest (evolutionarily) and most universal
Chemical sense
Sour detecting cells allow protons to enter through a channel to inhibit and cause what?
Inhibit specific K leak channel and depolarize the cell
Used to determine what is food and what is poison
Taste
Multiple of these are in each taste cell (4-11) for bitter
T2Rs
Molecules being detected for taste
Tastants
Some cells detect both sweet and umami, but never these two combination
Bitter and umami or bitter and sweet
Where is the sensory part of a taste receptor cell
Apical end (facing out)
These are located on paella (bumps on tongue)
Taste buds
Taste bud cells that respond to sour taste
Type III
These are found in the stomach, intestines, and lungs
T2R receptors (bitter)
The transmitters taste cells use to generate receptor potentials and depolarize
5HT and ATP
How do most cells respond to taste? Is this always the case?
Most cells respond strongly to one taste but some can respond to more than one
How many basic tastes are there?
5
Each one of these uses one mechanism, not all are understood however
Each basic taste
The heteromeric dimers that make up sweet receptor cells that detect all sweet tastants
T1R2+T1R3
Are taste receptors exclusive to the mouth?
No, they are in the pharynx, lungs, intestines, testis, etc.
Taste bud cells tuned to detect one of three tastes (bitter, sweet, or umami)
Type II
Various ones of these are found in the heart, kidneys, testis, thyroid, and other organs/cell types including the brain
Taste receptors
How are taste cells dispersed on the tongue?
They are spread out and not located for specific tastes
Taste bud cells that are probably progenitors of other taste sensing cells
Basal cells (Type IV)
Monitor internal environment (O2, CO2, proteins, etc), involved in chemical communication and integration
Chemoreceptors
Each taste bud contains how many tase bud cells?
50-150 (1% of tongue epithelium)
A PLC and taste cell specific cationic channel
TrpM5
Activate the same second messenger system as for bitter using GPCRs
Sweetness (type II cells)
How do different tastes stimulate different responses in the brain?
They stimulate responses in different areas (insular taste cortex)
Brodmann’s 36
Primary gustatory cortex
These cells are likely involved in salt detection
Type I and type III
Taste bud cells that are presynaptic, form synapses, have synaptic vesicles, and use VG calcium channels
Type III
This taste uses T1R2+T1R3 receptors (type II)
Sweet
Signals to the primary gustatory cortex are carried in this manner
Ipsilaterally, same side
This taste uses T2R receptors (type II) only
Bitter
This is detected by an mGluR for umami detection
Glutamate
High levels of salt are aversive and activate these cells
Bitter (type II) and sour (type III)
K, Mg, and caffeine all taste this way
Bitter
Both of these are needed for flavor detection
Taste and smell (gustation and olfaction)
The G protein present in some taste cells
Gustducin
Smell, combinations of receptors, pain, texture, visual cues, and temp all contribute to this
Flavor
No taste perception
Ageusia
The G protein used in sweetness
Gustducin and probably others
Taste bud cells like glial cells that may be Na+ sensing, but we aren’t sure
Type I
Two families of taste receptor genes that are GPCRs (using gustducin) in type II cells for detecting bitter
T1R and T2R
Things with very different structures can have this taste
Sweet
These 3 cranial nerves carry gustatory axons
VII (facial), IX (glossopharyngeal), and X (vagus)
When exposed to chemicals, taste cells do this
Generate receptor potentials to depolarize
Where do gustatory axons first synapse?
Gustatory nucleus in medulla
Na+ enters through these channels
Amiloride sensitive Na+ channels (others probably involved like TRPV1 and TMC-1)
This NT is released by sour sensitive cells
5HT