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37 Cards in this Set
- Front
- Back
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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 |
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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 |
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How are taste (gustation) and smell (olfaction) intertwined? |
Signals from both systems converge at the caudal orbital cortex. |
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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) |
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Describe the gustation pathway. |
gustatory receptor cells send signals to--> medulla--> thalamus--> caudal orbital cortex |
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What are papillae? |
- Papillae are the elevated structures on the tongue that contain taste buds - Each papillae contains 1-700 taste buds |
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Describe Fungiform papillae. |
- Found primarily at front of the tongue - Have taste buds on the surface - Connect to the VII cranial nerve
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Describe Foliate papillae. |
- Found primarily at back of the tongue - Have taste buds on the sides - Connect to the IX cranial nerve |
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Describe Circumvallate papillae. |
- Found primarily at back of the tongue - Have taste buds on the sides - Connect to the IX cranial nerve |
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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 |
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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 |
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What are the 5 types of human taste? |
- Sweet - Umami (savory) - Bitter - Salty - Sour |
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Describe "sweet" |
- usually perceived as pleasant and desirable - G-protein-coupled receptors - 1 receptor type (genes: T1R2 + T1R3) |
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Describe "umami" |
- savory/protein - usually perceived as pleasant and desirable - G-protein-coupled receptors - 1 receptor type (genes: T1R1 + T1R3) |
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Describe "bitter" |
- often perceived as noxious, esp in high concentrations - G-protein-coupled receptors - 30 receptor types (30 different TS2R genes) |
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Describe "salty" |
- usually perceived as pleasant and desirable - Ion channel for Na+ - gene: ENaC |
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Describe "sour" |
- often perceived as noxious, esp in high concentrations - Ion channel for H+ (acid) - gene: PKD2L1 |
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What are other sensations that contribute to taste perception? |
- aromas/odors (volatile chemicals) of food: olfactory system - vision: appearance of food influences taste perception |
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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 |
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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 |
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What do umami genes (T1R1+T1R3) detect? |
- L-glutamate - Nucleotide enhancers |
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What do sweet genes (T1R2+T1R3) detect? |
- sugars - artifical sweeteners - D-amino acids - glyceine - sweet proteins (carbohydrates) |
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What do bitter genes (~30 T2Rs) detect? |
- cycloheximide - denatonium - salicin - PTC - saccharin - quinine - strychnine - atropine |
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What do sodium genes (ENaC) detect? |
- low NaCl - sodium salts |
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What do sour genes (PKD2L1) detect? |
- acids |
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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 |
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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 |
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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 |
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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 |
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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 |
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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) |
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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 |
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What is "anosmia"?
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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) |
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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 |
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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 |
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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 |
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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 |
