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37 Cards in this Set

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  • Back

Why is the taste and smell of food important?

- Provides info about whether a food is harmful (aversive tastes and odors)

- Provides info about whether a food is beneficial (pleasant tastes and odors, nutrient detection)

- Initiates physiological response necessary for digestion and processing of food

Describe human sensory ability.

- Humans use both taste and smell to collect info about foods

- Compared to other mammals, humans have a relatively weak sense of smell

- Even with limited olfactory receptors: professional perfumers can reportedly detect ~5000 odorants, professional wine tasters can reportedly detect >100 flavor/aroma combos

How are taste (gustation) and smell (olfaction) intertwined?

Signals from both systems converge at the caudal orbital cortex.

Describe the olfaction pathway.

olfactory receptor cells send signals to--> olfactory bulb--> primary olfactory cortex--> caudal orbital cortex (also other areas of the cortex, like the amygdala)

Describe the gustation pathway.

gustatory receptor cells send signals to--> medulla--> thalamus--> caudal orbital cortex

What are papillae?

- Papillae are the elevated structures on the tongue that contain taste buds

- Each papillae contains 1-700 taste buds

Describe Fungiform papillae.

- Found primarily at front of the tongue

- Have taste buds on the surface

- Connect to the VII cranial nerve

Describe Foliate papillae.

- Found primarily at back of the tongue

- Have taste buds on the sides

- Connect to the IX cranial nerve

Describe Circumvallate papillae.

- Found primarily at back of the tongue

- Have taste buds on the sides

- Connect to the IX cranial nerve

Describe taste buds.

- Human have ~10,000 taste buds

- Each taste bud contains 50-80 specialized cells

- Each taste bud can detect one or more taste, and potentially all the tastes

- Taste buds on the epiglottis connect to the X cranial nerve (vagus nerve)

- Some areas of the tongue respond better to certain taste

Describe taste pores.

A small opening at the top of the taste bud, where cells are exposed to the chemicals in the mouth and receptors on these cells can be activated

What are the 5 types of human taste?

- Sweet

- Umami (savory)

- Bitter

- Salty

- Sour

Describe "sweet"

- usually perceived as pleasant and desirable

- G-protein-coupled receptors

- 1 receptor type (genes: T1R2 + T1R3)

Describe "umami"

- savory/protein

- usually perceived as pleasant and desirable

- G-protein-coupled receptors

- 1 receptor type (genes: T1R1 + T1R3)

Describe "bitter"

- often perceived as noxious, esp in high concentrations

- G-protein-coupled receptors

- 30 receptor types (30 different TS2R genes)

Describe "salty"

- usually perceived as pleasant and desirable

- Ion channel for Na+

- gene: ENaC

Describe "sour"

- often perceived as noxious, esp in high concentrations

- Ion channel for H+ (acid)

- gene: PKD2L1

What are other sensations that contribute to taste perception?

- aromas/odors (volatile chemicals) of food: olfactory system

- vision: appearance of food influences taste perception

Which sensations are mediated by the Trigeminal nerve (V cranial nerve) innervating the tongue and mouth (Chemesthesis: pain touch, thermal sensations)?

- pungency/heat (e.g., capsaicin in peppers, alcohol): pain neurons

- coolness (e.g., menthol): temperature-sensitive neurons (without temperature change)

- texture: sensory neurons

- astringency (e.g., tannins, calcium oxalate in unripe fruit, tea, dry wine): puckering of the mucus membranes

- other: numbness, heartiness, metallic taste, calcium

Describe sensory cells of the taste buds.

- taste buds contain multiple sensory cells

- each sensory cell detects one type of tastant

- sweet, umami, bitter-detecting cells release ATP when stimulated by a tastant

- salt and sour-detecting cells release serotonin when stimulated by a tastant

- gustatory neurons are activated by ATP or serotonin--> signal to the brain

What do umami genes (T1R1+T1R3) detect?

- L-glutamate

- Nucleotide enhancers

What do sweet genes (T1R2+T1R3) detect?

- sugars

- artifical sweeteners

- D-amino acids

- glyceine

- sweet proteins (carbohydrates)

What do bitter genes (~30 T2Rs) detect?

- cycloheximide

- denatonium

- salicin


- saccharin

- quinine

- strychnine

- atropine

What do sodium genes (ENaC) detect?

- low NaCl

- sodium salts

What do sour genes (PKD2L1) detect?

- acids

What is "PTC"?

- Phenylthiocarbmide (PTC) is a bitter chemical similar to similar to a chemical found in cruciferous vegetables

- ~70-75% of people can taste it (with varying sensitivities) and ~25-30% of people can't taste it

- taste is mostly determined by a variation in the TAS2R38 taste receptor gene

Describe the "PTC taste" example of how genetics can influence taste perception.

- the ability to taste PTC has a dominant pattern

- one copy of the "T" allele means you can taste PTC

- however, the T allele only accounts for ~85% of the variance in tasting ability

- taste ability can decrease with dry mouth, can change over time, and is influenced by foods eaten

Can humans taste fat?

- detection of fats has been atributed to sensing the texture and aroma, and to post-ingestion signaling

- rodent studies suggest that taste also contributes

What is the evidence for fat taste in humans?

- 2 receptor candidates are found in human taste cells: CD36 (long-chain fatty acid transporter), GPR120 (G-protein coupled receptor activated by long-chain fatty acids)

- FFAs in foods are in sufficient concentration to activate receptors

- receptor binding elicits a cellular signaling response

- fats in foods elicit a physiological response that prepares the body for fat digestion

What is the missing evidence for fat taste in humans?

- FFAs in foods are detected, but it is unknown if they are perceived

- the other 5 taste senses are both detected and perceived as distinct sensations

- unknown if fat can be perceived, bc odor and texture are prominent above the level of detection

- oxidized or reverted FAs, and FFAs at high concentrations are perceived as tasting bad

Is fat taste relevant to obesity in humans?

- most studies indicate that those who are more sensitive to the FA C18:1 (oleic acid): have lower energy intake, consume less total dietary fats, are better at detecting the fat content of food, have lower BMIs

- high fat diets in humans: dec fat perception in the mouth, dec release of hormones from the gut that respond to fat in the diet (satiety hormones)

Describe odorant perception.

- the olfactory bulb sends info to many areas of the brain

- one area is the limbic system, which is an ancient part of the brian involved with emotion and memory--> particular smells can bring back strong, emotion-laden memories

- smell perception dec with age, can be an early sign of Alzheimer's Disease

What is "anosmia"?

A lack of sense of smell (affects ~6 million Americans), can be cause by respiratory tract diseases, head trauma, genetics, aging (60% of those older than 80)

Taste receptors are found in what other parts of the body?

- sweet taste receptors are found in gut, pancreas, bladder, brain, bone, testes, and adipose tissues

- in the gut: it may be involved in luminal glucose sensing, release of some satiety hormones, expression of glucose transporters, and maintenance of glucose homeostasis

- it's proposed to regulate adipogenesis, bone biology, and reproduction

Describe odorants.

- odorants are dissolved in the mucus on a small patch of epithelium in the back of the nose

- odorants bind to receptors on the cilia of an olfactory sensory neuron

- individual olfactory sensory neurons only express one type of odorant receptor

- each odorant may activate more than one receptor type

- 1,000s of aromas/odors may be perceived

Describe odorant receptors.

- odorant receptors are G-protein coupled receptors

- discovered by Linda Buck and Richard Axel in the 1990s

- although the receptors have the same basic structure, they are very diverse in amino acid sequence

Describe odorant receptor signal transduction.

- odorants bind to receptor--> receptor is activated

- G-protein is activated

- G-protein activities the enzyme adenylyl cyclase, which produces cAMP

- cAMP activates an ion channel that causes influx of calcium/sodium into the cell

- influx of ions causes a cascade of chemical reactions in the cell (and depolarization), which then leads to release of neurotransmitter onto connecting cells in the olfactory bulb