Sense of Taste!
Part two
*Basal epithelial cells*: Dynamic stem cells that divide every 7-10 days. They make new gustatory epithelium cells (?)
Basic Taste Sensations!
-*Sweet*: Sugars, alcohols, saccharin (a sugar substitute) and some amino acids. -*Sour*: Hydrogen ions in solution. -*Salty*: Metal ions (inorganic salts), particularly sodium chloride. -*Bitter*: Alkaloids like quinine and nicotine, caffeine and non-alkaloids like aspirin. -*Umami*: Amino acids glutamate and aspartate. Basically meaty stuff. -Potentially a sixth one but not as important is a type of fatty taste (long chain fatty acids form lipids).
How tastes preferences have homeostatic value
-Can guide intake of beneficial and harmful substances. -Our general dislike of bitterness and sourness keeps us from eating poisonous/spoiled foods.
What is required to taste a chemical?
-It must be dissolved in saliva (You can't taste things with a dry tongue). -Must diffuse into taste pore (Your taste buds are under these, see above image if confused). -Must make contact with gustatory hairs (carries taste to taste buds)
Why is taste important?
-It triggers reflexes involved in digestion, like increasing secretion of saliva in mouth and gastric juice in stomach. -Can also initiate protective reactions like gagging and vomiting.
What influences taste, aside from taste itself?
-Taste is 80% smell, so your nose. This is due to olfaction being much more sensitive than gustatory. -The thermoreceptors, mechanoreceptors (touch) and nociceptors (pain) can enhance or detract from taste. -Special case for nociceptors is spicy foods excite them, causing some people to experience them as pleasurable like spicy foods.
How taste receptors activate
Binding of food chemical (tastant) depolarizes gustatory epithelial cell membrane, releasing NTs [familiar?]. NTs binds to dendrite of sensory neurons and initiates a generator potential which eventually leads to an AP. -Different gustatory cells have different activation times. For example, bitter sets off the fastest as they are the most sensitive. -All will adapt in 3-5 seconds, fully finish in 1-5 minutes.
General structure of buds (cells, hairs, pores, etc), part one.
Each bud consists of 50-100 epithelial cells varying from: -*Gustatory Epithelial cells*: Taste receptors that have *microvilli* (a large number of small projections) called *gustatory hairs*. These project (extend out to) into *taste pores* which are bathed in saliva. -Sensory dendrites around gustatory epithelial send taste signals to brain. -Three types of gustatory: one sends ATP, one lacks synaptic vesicles and one releases *serotonin*.
Taste Transduction [Transduction is the conversion of sensory info to neural info].
Gustatory epithelial cell depolarization is caused by: -Salty taste due to Na+ (sodium) influx that causes depolarization. -Sour due to H+ (hydrogen) acting intracellularly (opening channels that let cations in). -Unique receptors for sweet, bitter and umami. All are coupled to G protein *gustducin*. Activation causes release of stored Ca2+ which opens cation channels, depolarizing and releasing NT ATP.
What are taste buds, location of taste buds and their structures?
Taste buds are sensory organs for taste. -Most of the tens of thousands of taste buds on the tongue as *papillae*. Three types of papillae: *Fungiform*, the easiest to see ones. All over the front of the tongue; mushroom-shaped structures. *Foliate*: Sides of the middle of the tongue. *Vallate*: Large taste buds forming a V at the back of the tongue.
Gustatory pathway (which cranial nerves move impulses from tongue to brain?)
Two main cranial nerves carry taste impulses: -Facial Nerve (7) carries impulses from anterior (front) two thirds of tongue. -Glossopharyngeal (10) carries impulses from posterior 1/3 and *pharynx* (membrane lined cavity behind nose and mouth). -*Vagus Nerve* transmits from epiglottis and lower pharynx.