Taste

Bitter: usually means poisonous, but what is an example of a built-in system that helps us eat bitter things even though they don't taste great? How many genes for bitter receptors are there and what does that tell us?

A compound (AMP) inhibits some bitter sensation, which is present in mother's milk. 25 bitter receptors on 3 chromosomes

What has cross-modality matching told us about taster status?

Ability to match intensities of sensations coming from different sensory modalities. Self-explanatory

What are adaptation and cross-adaptation?

Adaptation: Loss of taste (any stimulus) w/ constant stimulation. i.e. why saliva isn't salty Cross-adaptation: Reduced response to one primary taste after exposure to another

Know the disorders of taste we discussed. Also know the terms aguesia, hypogeusia and dysguesia. Why can altered taste perception be so bad for overall health?

Aguesia: total loss of taste Hypoguesia: decrease in taste of all or specific primary tastants Dysguesia: distorted taste Cannot eat certain things because receptors are not working, or can eat toxins without receptors alerting body of dangers

Purpose of 4 Primary Tastes

Alerts of Dangers and Needs: Needs: 1) Ions/basic elements (salt) for proper nerve & muscle function, die w/o it. 2) Energy: Carbs (sweet taste) 3) Building blocks for proteins, amino acids (umami) Dangers: Poisons: spoiled food/bacteria (sour), toxic chemicals (bitter)

Bitter, sweet, and umami APs

Bitter, sweet, and umami: Molecule binds to metabotropic receptor on microvilli, G-protein activated, 2nd messenger made, Ca2+ let into cell from internal stores Na+ into cell as well, NT release, AP in taste nerve.

Anatomically, what is the difference b/t a taster and a super-taster?

Combination of genetic PROP status and number of fungiform papillae on tongue.

What brain regions (in order) get info about taste?

Crainal nerves (VII, IX, X)-> Medulla & pons-> Thalamus-> DM (connections w/ prefrontal cortex, hedonic nature of taste) and VP (same as touch from face, projects to primary taste cortex)

What are the arguments for and against umami being a primary taste?

For: Signals protein, therefore plays important role in nutrition. Against: Unperceptible in many protein-rich foods & some people like it and others don't (basic taste-responded to in same way by most people)

How do we choose foods?

Hard-wired taste preferences: meet evolutionary needs, facial expressions of newborns to primary tastes i universal. Learned responses to food flavors: Signals back from gut: liking foods that provide important nutrients, learned taste aversions

What are the roles of the insular cortex and the orbitofrontal cortex?

Insular Cortex- Primary taste cortex, gustatopic in mammals Orbitofrontal Cortex-Association cortex, temp, touch, smell, taste, good for flavor

What is flavor?

Metasensation created by brain based on taste and smell. Food is chewed and swallowed and molecules are released into air outside mouth & forced up behind palate in nasal cavity (olfactory), known as retronasal olfactory sensations

Where do fibers of the taste cranial nerves synapse w/ taste cells

Nerve fibers are at the bottom of the taste buds and the response initiates an action potential along nerves VII, IX, and X to the brain.

Taste pore

Opening into taste bud where molecules in saliva travel into to get to taste bud

What types of somatosensory info do we get from the mouth that is relevant to the entire taste experience? What cranial nerve carries that info?

Pain (burn of acid, biting tongue), texture (viscous, creamy, thick), Temp (peppermint is cool, and actual temps of food). Trigeminal Nerve (CN V)

Understand the anatomy of the taste system: know the names of the different types of papillae; what/where are the taste buds, and taste cells

Papillae are ridges on tongue, 4 types, 3 w/ taste function. Receptor proteins->taste cells-> taste buds->ridges of papillae

Salt: what can affect salt preference and perception?

Preference: No salt preference until 6 months old, Cl-/Na+ deficiency in infancy-> increased Na+ preference in adulthood. Offspring have increased Na+ pref for mothers with bad morning sickness, infants fed starchy foods causes increased salt preference Perception: Low Na+ diet increases perceived intensity of saltiness

Sweet: What do you know about the receptors for sweet tastes and their relationship to artificial sweeteners?

Receptors are tuned so glucose fructose and sucrose stimulate them while biologically useless sugars don't. 3 genes=3 G protein-coupled receptors. 2 receptors dimerize to form main sweet receptor, 1 signal from receptor, regardless of sweetener stimulates it.

Salt AP

Salt: use ionotropic receptors. Na+ enters thru channel on microvilli, depolarization allows Na+ and Ca2+ in thru voltage-gated channels, NT releases, leads to AP in taste nerve

How does the perception of bitter change across the lifespan of women?

Sensitivity to bitterness intensifies w/ pregnancy and diminishes post-menopause

Understand the physiology of the taste receptors

Some receptor cells synapse on nerve fibers, 3 separate cranial nerves. Fungiform papillae: Some fibers branch, >1 cell per fiber & >1 fiber per cell

Sour AP

Sour: Ionotropic. Acids in H2O have free proton H+, this proton blocks K+ channel, K+ can't leave cell, depolarizes cell, Na+ and Ca2+ into cell thru voltage-gated channels, NT releases, AP in taste nerve

How do we perceive proteins and fat? What is the importance of the gut?

Stimulate receptors to small degree in mouth, glutamate receptors for protein, fatty acid receptors for fats, stimulate receptors in gut bc more broken down by then. Gut sends signal back to brain via vagus nerve to like sensory properties of that food

For what primary tastes do humans show "specific hungers"? What is some evidence for these?

Sweet & Salty. Ex: Boy craved salt, salt-restricted during hospital stay, died, adrenal gland tumor caused body to lose sodium, craving for salty foods would have kept him alive. Insluin injections increase craving for sweets.

What is necessary for something to be able to cause a specific hunger?

The need for a nutrient causes body to crave it. Nutrient needs to be associated w/ sensory cue, doesn't work if nutrient doesn't have a taste.

How does the brain differentiate b/t tasting or smelling something?

The tactile information indicates that something is actually in your mouth, as opposed to smelling it when nothing is in your mouth.

What cranial nerves innervate the tongue?

Vagus Nerve (CN X; in back), Glossopharyngeal Nerve (CN IX, mid), Chorda Tympani Nerve (branch of facial nerve, CN VII; front), Trigerminal nerve (CN V) for touch, temp, pain.

Water Essay:

Water is below adaptation, so it doesn't cause a loss of taste. For example, water following adaptation to dilute acids tastes sweet, water following urea tastes salty, and water following NaCl tastes bitter or sour.

Do we differentiate b/t bitters? Why or why not?

You don't differentiate b/t bitters b/c each type of bitter receptor doesn't necessarily have a projection neuron. Also, there's multiple bitter receptors allowing for variety of responses to bitter compounds amongst all people. Genetic make-up differentiates intensities/types of bitter amongst humans.

What aspects of taste are probably coded using labeled-line and which ones are probably coded using cross-fiber patterning?

labeled-line: When one type of receptor is stimulated, no need to cross between different receptors b/c taste is so accurate to a primary receptor Cross-fiber: When trying to ID type w/in a primary (kind of sweet, kind of salty. When tastants stimulate more than 1 type of receptors.

Genetically and behaviorally, what is the difference b/t a non-taster and a taster/supertaster? What are some health consequences of taster status?

tt= non-taster, TT or Tt= supertaster/taster. Health consequences: Tasters/supertasters taste bitter things as more bitter, avoid veggies/alcohol. Fats ca be unpleasant, fewer high fat foods= less cardiovascular disease?

Can we differentiate b/t real sugars and artificial sweeteners, and if so, how?

yes, A receptor (T1R3) can function alone to respond to high concentrations of sucrose, which is why we differentiate b/t sucrose & artificial sweeteners (cross-fiber patterning)