Test 2: Taste

How are unipolar neurons arranged for taste mechanism?

One end connects to the tongue and one end enters the medulla. It all happens on the same side of body. (so left stays on left)

Describe the two sides of the taste cell

One side is the head which is exposed to the papillae groove saliva. The other side goes deep into the tongue where it will make synaptic contact wither free nerve endings

What is the name of the chemical that supertasters taste?

PROP

Papillae

Rough area found all over the tongue. They are grooves which allow saliva with chemicals to pass thru. There are 3 types. Each papillae has 2 grooves with many taste buds with taste cells.

Describe the flow of saliva with chemicals through tongue

Saliva flows from top of tongue where it hits the papillae grooves then goes down, it will then go to a taste bud, and then to a taste cell which has a receptor which will then bind and allow the transduction event of tastant binding to occur

Types of non-conventional tastes

Spicy (hot/heat), Minty (cold/cool), water, BAP

TPRV1

Spicy receptor/ Pain receptor/Vanilloid receptor/Hot receptor/Heat receptor --- all the same thing just many names

Describe the flow of chemical when tastant chemical hits the receptor

When the tastant binds to the taste cell receptor, it will cause an EPSP (type of ion influx depending which taste), this will then neurotransmitter release to the free nerve endings, which will bind to it, cause a EPSP depolarization (not action potential), and then relay the signal up to brain stem

TRPM8

activated below 25C, found in plants, trick you into thinking something is cool like mint cuz they activate cool receptors as antagonists

TRPA1

activated by below 17C, activation leads to the feeling of painful cold

Labeled Line Theory

concept that each receptor responds to a very limited range of stimuli and has a direct line to the brain when it becomes activated

Disinhibition

"Inhibiting an inhibitor" with the net effect being excitation

Sweet Taste Transduction Pathway

-- A sugar tastant such as sucrose binds to T1R2 or T1R3 and causes the two to link up together (Dimerize) and the receptor is activated -- G protein is activated which turns on adenylate cyclase --> adenylate cyclase converts ATP to cAMP -- cAMP goes and travels to potassium channel and closes it which results in the EPSP graded potential which triggers neurotransmitter release

Describe the heat receptor/spicy mechanism

-- Ambient temperature above 42C or antagonist such as capsaicin (found in peppers) trigger receptor to open -- cations flow inward and depolarization results

How come bitter causes efflux and umami causes influx of calcium. Whats the difference? How come the picture shows calcium coming in for both?

-- Ask

3 types of papillae

-- Circumvallate -- Foliate -- Fungiform

Salty Transduction Pathway

-- Na+ ions move down there concentration gradients thru papillae and cause a depolarization/EPSP -- This causes Neurotransmitters to be released onto free nerve endings (cranial nerve fibers) which will signal the brain there was salty taste

Sour taste transduction pathway

-- Normally potassium channels are open allowing potassium deflux out of the cell -- Acidic solutions high in protons (H+) flow into the cell and inhibit potassium channels from functioning -- This causes a build up of positive ions in the interior and thus results in an EPSP/depolarization which is released onto nerve endings

5 Conventional Kinds of Taste/tastants that we respond to with specific receptors for each

-- Salty -- Sour -- Sweet -- Bitter -- Umami (protein rich)

Bitter Transduction Mechanism Pathway

-- Tastant binds to T2R receptor -- G protein is activated which turns on phospholipase C (adenyline cyclase equivalent) -- phospholipace C produces IP3 (cAMP equivalent) -- IP3 a massive efflux of calcium into cell which causes an EPSP then neurotransmitter release

Supertaster 2 Qualities that differenciate them

-- They have more papillae on their tongue; fungiform papillae -- They have more taste buds which means that have more taste cells which means more taste receptors. And they have extra receptors for the given ratio. (This means that they are more sensitive to certain types of chemicals since they have more detectors)

Umami Transduction Pathway

-- amino acid glutamate binds to g protein metabotropic receptor and causes T1R1 and T1R3 (heterodimers) to come together and activate g protein. -- G protein activates adenylate cyclase -- Adenylate cyclase converts ATP into cAMP -- cAMP causes an influx of calcium which causes EPSP then neurotransmitter release

How many different kinds of receptors do we have for bitter? Why? Any other important notes?

30+. Bitter receptors help us define bad/danger so we wont swallow it. We taste all bitter as the same but we have multiple receptors to discern if any is harmful regardless of taste.

What gene codes for supertasters?

A single genetic mutation in the bitter receptor gene

What activates a taste cell?

A tastant from environment

Interesting facts about sea elegan and taste

About a third of its 302 neurons are dedicated to only taste. They use their neurons to take into account chemicals, food and vitamins

What is the vanilloid receptor activated by? What does it do on tongue?

Activated by ambient (surrounding) hot temperature or agonists chemicals that act like hot temperature. It makes us perceive on our tongue as hot/spicy.

TRPA1 and TRPM8

Activated by cold

Supertaster

Capable of tasting flavors that most of us can't. They have a special sense for a bitter tastant that most of us cannot taste

Where is the cell body of the neuron that has free nerve endings in the taste cell located? Where does it transmit info before going to brain stem?

Cell body is found in ganglia in back of head which then goes to brainstem

Two ways to produce an EPSP

Direct depolarization (gas) or inhibiting an inhibitory effect (removing break)

True or False: Taste cells exhibit action potentials. Explain

FALSE: When transduction occur, essentially, when a chemical binds to a receptor on the outside of the taste cell, the taste cell will respond with a membrane potential change. IT WILL NOT BE AN ACTION POTENTIAL. It will be a depolarization/EPSP. TASTE CELLS DONT HAVE A MEMBRANE THRESHOLD POTENTIAL. They will not fire an action potential when an EPSP gets large enough. Instead, the EPSP will get larger and larger and never generate an action potential. This is called a graded potential (continuous).

True or False: The different types of papillae can detect different tastants. Explain

False. The ability to detect different tastants is uniform across the tongue. They dont discriminate. There is an equal distribution across the tongue. Each papillae detects all 5 tastes. However, not each papillae is structurally the same.

Fungiform Papillae

Found at the tips of tongue. They are involved in supertasting. Very small

Circumvallate Papillae

Found in the back of tongue. Big large bumps

Foliate Papillae

Found in the middle of tongue. Medium sized

Unipolar neuron cell

Found within the ganglia of the head (cranial nerves). They have one process that splits into two. One end is axon like, and one end is dendrite like (Free nerve endings).

Heterodimer vs dimer

Heterodimer is two protein parts that are different (T1R1 + T1R3). Dimer has both equal parts (T1R2 + T1R3)

What is artificial Umami used in fake foods?

MSG

Supertaster implications on health?

Never drink alcohol because it tastes much worse than normal (Advantage). Never smoke because it tastes extremely bitter (Advantage). Tends to cause them to have a higher BMI (Disadvantage).

Do taste cells follow labeled line theory? If not, what happens instead?

No. Each taste cell depolarizes in response to all types of tastes. This taste cell doesnt know the difference between salty and sweet. It increases the rate of action potentials irrespective to the taste quality. (Dr. Lorenzo research: clarify he supports it or disproves it?)

AVI

Non-supertaster genotype

Describe the central taste pathway. Be specific

Starting on one side (we'll call it left) -- Taste cells release neurotransmitter onto free nerve endings which cause sodium influx (EPSP) into free nerve endings -- The free nerve endings allow the graded potential to travel to the unipolar neuron cell body and then out into the axon like ending into the brain stem (Nucleus of the solitary tract) -- The brainstem axon terminals synapse with the thalamus AKA the Relay Station (ventral posterior medial nucleus) -- The thalamus send their axons up into the gustatory cortex (located in frontal lobe, insula inside the sylvian fissure) where taste will finally be processed and perceived Ending on one side (still left)

Preference for sugar, bitter, and spicy

Sugar -- biologically prefer it Bitter -- biologically avoid it Spicy/minty-- culturally transmitted phenomenon

PAV

Supertaster genotype

Which 3 taste types operate by Metabotropic receptor transduction?

Sweet/Bitter/Umami

What is the name of the vanilloid receptor in science terms?

TPRV1

Chemicals that we refer to and that have flavor are called

Tastants

What can change the membrane potential regarding taste? What cant?

Tastants are chemicals that if detected can change the membrane potential. Chemicals that we do not taste will not change the membrane potential, and as a result we dont taste them. This is because we dont have the receptors for them.

The ability to detect certain types of chemicals when they are dissolved in the saliva of mouth and come into contact with your mouth-specific cells is called

Taste

T1R1

Taste Class 1 Receptor Class 1. Found in Umami

T1R2

Taste Class 1 Receptor Class 2. Found in Sweet

T1R3

Taste Class 1 Receptor Class 3. Found in sweet and umami

T2R

Taste Class 2 Receptor Class 0 (only one in class 2 taste). Found in Bitter

Taste cell

Taste cell is unique: it has a head which connects to groove portion of papillae. It has a tail end which makes synaptic contact with free nerve endings (Dendrite like processes)

So how does the brain know the difference between the types of tastes being present in the mouth if the taste cell responds equally to them?

Temporal code (more so than rate code for taste). The temporal spacing of the action potentials tells the brain about the difference between salty, sweet, and bitter.

Describe the concept of intensity in the salty taste pathway

The magnitude of the EPSP depends on the concentration of salt present in the food. The more salt the more EPSP cuz of a graded potential. The more EPSP the more neurotransmitter efflux on to the nerves. The more neurotransmitters, then the more signals will be taken to brain. So this allows us to experience INTENSITY. More salty = more EPSP = more neurotransmitter on fibers = greater intensity.

Cranial nerve fiber role in taste

They are a set of nerves that travel in part from tongue to brain stem

How do factories manipulate sugars like artificial sweeteners?

They take advantage of our tongue receptors to sweet tastes. They trick the receptor to think its the sweet ligand. So the ligand will bind and we will perceive sweet, however we will not metabolize it the same way we would with a natural sugar. IE: you could taste sucrose and also metabolize it into energy. Safrin can bind to receptor and you'll taste it as sweet, but you cant metabolize its energy.

True or False: The hotter the temperature, the more spicy it is perceived as

True

Type of tastant receptor thats responsible for protein amino acid like taste

Umami

Concept of Unilaterality

What happens on one side of body, stays on that side of body