Age, Taste and Smell

Age, Taste And Smell
One of the more puzzling consequences of old age is a decreasing ability to appreciate the taste of a fine meal. Actually, the problem is not only a matter of taste. It also has to do with smell.


Combined Senses
When we eat something, we rely on a combined sense of taste and smell to experience flavor. The next time you’re eating fruit-flavored candy, try this. Grab a handful of candy, close your eyes, and pick one. While pinching your nose shut, pop the candy into your mouth.


Chances are you’ll taste the tart sweetness of the candy, but you won’t recognize a particular flavor. Now let go of your nose. Presto! The savory flavor of banana-grape fills your mouth.


Taste is a limited sense; the taste nerves in the mouth and tongue only detect combinations of sweet, sour, salty and bitter. Flavors, on the other hand, vary widely, numbering in the tens of thousands. When we experience these many flavors, we use our nose as much as our mouth.


Smell And Flavor
For example, when you chew a piece of candy, you inhale the candy’s chemicals through your mouth and exhale them through your nose. As they pass through the nose, the chemicals trigger receptors that send smell and flavor signals to the brain.


The body tends to break down in old age, and taste and flavor receptors are no exception. Although taste buds in the mouth tend to lose some sensitivity, it is the decrease in the number of active flavor receptors in the nose that make it more difficult for elderly diners to truly savor an exquisite meal.
年龄与味觉和嗅觉的关系


人到老年，一个令人费解的苦恼就是对美味佳肴品鉴能力的降低。事实上，问题不单单出现在味道上，同时还出现在嗅觉上。


感觉融合
当我们吃某样东西的时候，我们依赖融合了的味觉和嗅觉去体验味道。下一次你吃水果糖时，不妨试一试。抓一把糖果，闭上眼睛，随意挑选一颗。捏着鼻子把糖果放进你的嘴里。


你可能尝到糖果的酸甜的味道，但是你分辨不出独有的味道。现在让你的鼻子自由呼吸，转眼间，香蕉葡萄那可口的味道布满你的口中。


味觉是被限定的感觉，你口中和舌头上的味觉神经仅仅能够分辨出酸，甜，咸，苦。但味道多种多样，有上万种之多。当我们品尝这些味道的时候，鼻子和嘴一样功不可没。


嗅觉和味道
举个例子来说，当你嚼一块儿糖，你用嘴来吸收它们的化学成分，再用鼻子释放出来。当她们通过你鼻子的时候，这些化学成分激发受体，把嗅觉和味道的信号发送给大脑。


到了老年，身体衰退，当然，味觉和味道受体也不可幸免。口中的味蕾慢慢失去一些敏感性，鼻子中那些活跃的味道受体的减退让老年人更加困难地去享受精致佳肴。


【本译文由普特网友 sandyfc 提供】


PS：食物吃进嘴里，在牙齿和唾液酶的共同作用下被磨碎。食团很快就会接触到舌乳突——舌体上遍布的几千个如结节般的突起 ，每个舌乳突里有50～100个味觉细胞，它们像洋葱或花瓣那样叠加在一起，形成一朵朵含苞待放的花朵那样的结构——我们称之为味蕾。这些细胞里都“装“有化学感受器，能辨别5种基本味道——苦、甜、酸、咸，这4种基本味道。然而，它们并不能产生我们所感觉到的，复杂的口味。我们得靠鼻子才能感觉到复杂的口味。当你把食物吃进嘴里时，适量的气味分子被顺道压入口腔根部，进入鼻腔；鼻腔中的气味感受器会检测到大量挥发性化学分子，而正是这些分子，形成了食物错综复杂的口味。这种鼻后嗅觉在生理学上与我们嗅闻食物的动作没有任何关系。人类的大脑能知道气味信号从何而来——是来自鼻孔，还是来自嘴？如果是后者，大脑会将气味信号和味蕾传递出的味觉信号相结合，从而形成一种独一无二的感知——既不是嗅觉，也不是味觉，而是它们的混合体——口味。这个过程就像使燃料和氧气反应，产生火焰，彻底改变，不可逆转。
—《环球科学》