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Taste

People assume that we taste with our tongues, but this organ is only capable of distinguishing between four basic taste sensations. Combine this with our sense of smell, however, and we can enjoy a world of different flavours.

Taste is the crudest of our five senses, providing us with less information than any other. Though it helps us select and identify food and drink on a most basic level, our appreciation of food largely relies on our sense of smell which brings out all the subtleties and flavours of what we eat.

This is why loss of the sense of taste generally presents less of a problem to people than losing their sense of smell.

HOW IT WORKS
Like our sense of smell, our taste mechanism is triggered by certain chemicals. These are contained in the various substances that go to make up food and drink.

When we eat or drink, these chemicals dissolve in the saliva in our mouth and enter tiny pores found in the small protuberances, known as the papillae, studding the surface of the tongue.

Around these pores are our taste receptor cells which are more commonly known as taste buds. These are mainly found on the tongue, but there are also a small number at the back of the throat and on the palate.

SENDING INFORMATION
The dissolved chemicals then stimulate hairs projecting from the taste buds, that are connected to nerve fibres. These generate a nerve impulse which is relayed to the brain via one of two main nerves - the facial or the glossopharyngeal nerve. The brain then interprets the information relayed by the impulse and is able to identify the taste.

Taste buds can recognize four different taste sensations: sweet, sour, salt and bitter. The nerve receptors for each of these different tastes are located on separate areas of the tongue.

Sweet foods stimulate the taste buds at the tip of the tongue. The taste buds for salt are just behind the sweet buds at the sides of the tongue. Sour buds are situated a little further behind the salt buds and bitter are found across the back of the tongue.

Compared with all the other senses, our sense of taste is not very efficient. It's been estimated that a person needs to be in contact with 25,000 times as much of a substance to stimulate the taste buds than the amount that's needed to trigger our smell receptors.

ANALYSING SIGNALS
Nevertheless, the combined signals from the sweet, salt, sour and bitter taste buds allow the brain to identify a wide range of different foods, simply by analysing how strongly each differing taste sensation registers.

Strong flavours, such as the 'hot' flavour of spicy curries and similar foods, come about as a result of the mild stimulation of pain-sensitive nerve endings in the tongue. Temporary loss of the sense of taste or smell is most often caused by the nasal passages becoming swollen, blocked and inflamed because of a cold or a similar respiratory infection.

Medical conditions that lead to a dry mouth, or drugs that cause a dry mouth as a side-effect, may also interfere with taste, as the taste buds can only react to chemicals when these have been dissolved in saliva. Dry food gives virtually no immediate taste sensation, as it's only when it's been broken down with the help of sufficient saliva that we can begin to taste it.

However, ageing is the most common reason why we lose our sense of taste. As we grow older, our taste buds slowly degenerate and, in some cases, may cease to function altogether.

Loss of taste can also be the result of mouth inflammation, or stomatitis, cancer of the mouth, radiotherapy or damage to the facial nerve, resulting from an injury or a tumour. The facial nerve is connected to the muscles of the face and a small branch of it carries nerve fibres from the taste buds which are situated on the front two-thirds of the tongue.

WHAT CAN GO WRONG?
In Bell's palsy, the facial nerve suddenly ceases to function for no apparent reason and this is often accompanied by some loss of taste. But, even when the nerve on one side of the face is not functioning properly, the corresponding nerve on the other side will continue to relay taste information to the brain.

Before antibiotics were around to tackle ear infections, operations were often carried out to treat conditions such as mastoiditis - a complication arising from such infections. The branch of the facial nerve serving the taste buds, which runs alongside the lower ear, was often inadvertently damaged by the surgeon and a loss of taste was usually the result.

What causes more distress is when people completely lose their sense of smell - usually as a result of a head injury - because they no longer have the ability to really appreciate the full flavour of food.

EMOTIONAL RESPONSE
People who have lost their sense of smell also seem to be more prone to depression. Similarly, people who suffer from depression often complain about an unpleasant taste in their mouths.

Doctors don't really understand why this happens, but it may be connected to the close relationship between taste and smell.

In addition, research has shown that smell-analysing centres of the brain have close links with the emotional centres of the brain and psychiatrists have suggested that certain moods 'conjure up' specific tastes and smells.

Some people who have epilepsy experience an unpleasant smell or taste in their mouths when they are about to have a seizure, which usually serves as a warning.

     
     
White coating under tongue

Taste

 

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