What the tongue tells you Nov 8, 2011 18:02:05 GMT
Post by bixaorellana on Nov 8, 2011 18:02:05 GMT
extracted from ABC Science - Full article here[/url][/size]
... taste is still the most poorly understood of the supposed five classical senses of touch, sight, smell, hearing and taste.
Taste tells us about the nutrients in what we eat, and also warns us of potential toxins. So the sensation of sour might warn you against spoiled or unripe fruit; sweet might identify energy-rich foods; bitter could warn you of potential toxins; while salt could alert you to the presence of essential electrolytes.
Taste also does other stuff. Peppermint increases the production of saliva in the mouth, while cinnamon increases peristalsis in the gut.
Taste mostly, but not always, happens on the tongue.
The tongue is not smooth. It has quite a bumpy surface. These bumps, called papillae, are part of how you taste foods.
There are four different types or shapes of papillae. Three of them are connected to the sensation of taste because they not only contain tiny taste buds, but are also surrounded by taste buds.
A taste bud looks like a tiny sphere or ball. Taste buds themselves are in turn made up of taste-receptor cells. These taste-receptor cells are clustered together, within the taste bud, in groups of about 100.
They look like the segments of a kind of mini-orange, or perhaps like the staves that make up a wooden barrel.
These tiny taste buds lie between the cells that make up the surface of the tongue. They have a tiny hole opening onto the surface.
The taste-receptor cells extrude very fine hair-like filaments upwards into this tiny hole, and into the saliva that coats the tongue. These filaments sense or monitor the various chemicals that come and go on the surface of the tongue.
At the bottom end of the taste bud is a bundle of nerves. They carry the taste sensation towards the brain to be processed.
The average human tongue has between 2000 and 8000 taste buds, but it can vary between 500 and 20,000.
On average, a taste bud will survive for about seven to 10 days before it dies and is replaced.
There is a huge variation from one human to the next, in how well we detect some tastes.
One chemical used to test this is called PROP. Some people (called supertasters) perceive PROP as intensely bitter. Medium tasters recognise it as slightly bitter, while non-tasters cannot taste it at all.
This sensitivity is related to the number of taste buds on the tongue. Supertasters have 425 taste buds per square centimetre; medium tasters have about half as many (185); while non-tasters have about a quarter as many (96 taste buds per square centimetre).
Mind you, the so-called non-tasters are non-tasters only for the test chemical, PROP. They can still register the sensation of bitterness for other chemicals, such as quinine.
And, as an interesting aside, non-tasters are more likely to be alcoholics.
The main factor involved in how you taste stuff is genetic, in other words, inherited.
But there is also an environmental effect. For example, when people are severely depressed, their sensitivity to different tastes is much reduced. And this sensitivity returns to normal when they recover.
This altered taste has long been recognised as one of the neglected symptoms of depression. People suffering from an episode of panic disorder have a reduced sensitivity to bitter tastes.
On the other hand, people who are under stress become more sensitive to the bitter taste of saccharin.