Understanding The Complexities Of The Human Sense Of Smell
The human sense of smell is one of the most interesting
, and most delicate senses that we as humans possess. It works so intricately, enabling us to enjoy, taste, and remember.
Although the human sense of smell is feeble compared to that of many animals, it is still very acute. We can recognize thousands of different scents, and we are able to detect odors even in infinitesimal quantities.
Our smelling function is carried out by two small odor-detecting patches - made up of about five or six million yellowish cells - high up in the nasal passages. We may not be able to match the olfactory feats of bloodhounds, but we can, for example, 'track' a trail of invisible human footprints across clean blotting paper.
The human nose is in fact the main organ of taste as well as smell. The so-called taste-buds on our tongues can only distinguish four qualities - sweet, sour, bitter and salt -all other 'tastes' are detected by the olfactory receptors high up in our nasal passages.
Our smelling ability increases to reach a plateau at about the age of eight, and declines in old age. Some researchers claim that our sensitivity begins to deteriorate long before old age, perhaps even from the early twenties.
One experiment claims to indicate a decline in sensitivity to specific odors from the age of fifteen, if you can believe it. However, other scientists report that smelling ability depends on the person's state of mental and physical health, with some very healthy eighty year-olds having the same olfactory prowess as young adults.
Women consistently perform better than men on all tests of smelling ability. Schizophrenics, depressives, migraine sufferers, and very-low-weight anorexics often experience olfactory deficits or dysfunctions.
One group of researchers claims that certain psychiatric disorders are so closely linked to specific olfactory deficits, that smell-tests should be part of diagnostic procedures. Zinc supplements have been shown to be successful in treating some smell and taste disorders.
Although smoking does not always affect scores on smell-tests, it is widely believed to reduce sensitivity. Smell-sensitivity researchers have to be very careful about the odors they use in experiments, because a scent is not always a scent.
Many smelly substances activate not only the olfactory system, but also the 'somatosensory' system-the nerve endings in our noses which are sensitive to temperature, pain etc. This is why patients who have completely lost their sense of smell can still detect menthol, phenylethyl alcohol, and many other substances.
In a study testing their ability to perceive substances, it was found that many so-called odors are in fact affecting the pain and temperature-sensitive nerve endings, rather than the olfactory receptors. Out of forty seven substances, these people could detect forty five.
Only two substances could not be detected by the patients which were studied: these were decanoic acid and vanillin, which affect only the olfactory receptors, and can thus safely be classified as 'pure' scents. Some unpleasant smells do more than just annoy or disgust us-they actually cause us pain.
Although identification ability increases during childhood, even newborn infants are highly sensitive to some important scents. Recent research shows that newborn babies locate their mothers' breasts by smell.
In experiments, one breast of each participating mother was washed immediately after the birth. The newborn baby was then placed between the breasts.
Of thirty infants, twenty two spontaneously selected the unwashed breast. Other experiments have also shown that babies are responsive to very faint differences in body odor, but it is believed that infants are highly sensitive only to specific ones, rather than a wide range.
In terms of preference, however, one significant study showed that three year olds have essentially the same likes and dislikes as adults. Experiments conducted in the early seventies and replicated later revealed that children do not develop sensitivity until they reach puberty.
In these studies, nine year olds showed a pronounced insensitivity to two musks, although their ability to detect other them was the same as that of post-pubescent children and adults. There is no way to fully understand how and why our bodies work the way they do.
Any time you catch a scent on the breeze which reminds you fondly of a past memory or place, thanks those little cells that make that possible for you. Who knows where we would be without them?
by: Tommy Greene
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