Category Human Body

When do we lose our sense of taste?

Compared to other sensations (in particular smell) our taste sense is not very sensitive. It has been estimated that a person needs 25,000 times as much of a substance in the mouth to taste it as is needed by the smell receptors to smell it. However, despite this, the combination of the four types of taste buds responding to the basic tastes of salt, sour, bitter or sweet, enable a wide range of sensations to be determined as the brain analyzes the relative strength of the tastes. If we were to lose our sense of smell, almost all taste sensation would be lost as well. Eating oysters, for instance, where the smell is so important, would become a dull and totally ‘tasteless’ experience. That is why we sometimes lose our sense of taste when we have a cold because our nasal passages become blocked. You will gradually lose your sense of taste as you grow older, which is one reason why elderly people may no longer enjoy their food so much.

Fact File:

The human sense of smell is very poor compared to that of animals, such as dogs. Some dogs are able to identify and follow the smell of a person’s perspiration.

 

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When do we recognize a specific taste?

Tastes are detected by thousands of taste buds scattered along the tip, sides, and back of the tongue. There are also some near the lips, on the roof and sides of the mouth, and in the upper throat. Each taste bud is tiny – a microscopic bunch of about 50 cells which have furry, frilly tips. There are four main types of taste: sweet, sour, salty and bitter and these can be detected by different areas of the tongue. When molecules land on the frilly tip, the tastebud cells make nerve signals. These signals pass long small nerves which gather into two main nerves – the seventh and ninth cranial nerves. These signals then travel along them to the gustatory, or taste, area in the brain. You have around 10,000 taste buds on your tongue.

Fact File:

Smell enters the cavity behind the nose when you inhale. They also rise up from the back of the mouth as you eat, which is why smell is such an important part of enjoying food.

 

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When do people wear contact lenses?

If the eye is not exactly the right shape, or the lens cannot focus properly, you cannot form a clear image on the retina. In this case you may need to wear glasses to correct your vision. A short-sighted person can see nearby objects very clearly. A long-sighted person can see things in the distance while nearby objects are blurred. Contact lenses are an alternative to wearing glasses and many people prefer these. They are thin plastic discs that rest on the surface of the cornea. They act like the lenses of ordinary glasses. Most modern contact lenses are made from very soft material that does not cause any discomfort to the eye. Some lenses are only worn for just one day and then they are thrown away. It can be difficult to get used to wearing contact lenses and to putting them in the eye without scratching the delicate cornea. However, many people now prefer them to wearing glasses.

Fact File:

Film and television images consist of a series of rapidly changing still images, yet we see them as continuous motion. There is a slight delay between each of the images that appear on the screen. However, because this delay is so short, our brain is able to fill in the gaps and provide a complete picture of what is happening.

 

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When do we see images upside down?

The eyes are the body’s windows on the world. Like a video camera they detect a moving picture of the world and turn it into tiny electrical signals. These signals are nerve impulses which go to the brain to be sorted. In ancient times people thought that light shone out of their eyes onto what they looked at. Now we know that light rays pass from an object into the eye. Every second or two the eyelids blink and sweep tear fluid across the conjunctiva, washing away and dust and germs.

The image that forms on the retina when light passes through the lens is actually upside down. This is because of the way in which light rays are bent by the eye’s lens. The brain automatically turns the image the right way up, but you are never aware that this is happening.

Fact File:

There are six muscles to control the movements of each eye. Muscle (a) swivels it away from the nose; (b) towards the nose; (c) rotates it upward; (d) downwards; (e) moves it down and outwards and (f) moves it upwards and outwards.

 

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When do we suffer from referred pain?

Referred pain is a pain that’s source is in one place of the body but we feel it on another part of the body. Internal organs and structure are well supplied with nerves, but pain is widely spread and poorly located compared with skin sensations. Most of the pain is caused by stretching and contracting, as in the pain of colic. Internal pain will cause stimulation of local nerves in a portion of the spinal cord, and this makes it appear that the pain is coming from the skin which is supplied by the sensory nerves. The heart (1) and the oesophagus (2) refer pain to the neck, shoulders and arms. The uterus (3) and pancreas (4) refer pain to the lumber region. The kidneys (5) refer pain into the groin. Pain from the diaphragm may be referred to the shoulders as the phrenic nerve is formed from the spinal nerves in the neck, which also supply the shoulders.

Fact File:

Some areas of the skin are densely packed with nerve endings, as in the finger-tips, while others, as on the back, have comparatively few.

 

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When may the liver fail to function properly?

The liver has two vital roles to play: making (or processing) new chemicals, and neutralizing poisons and waste products. The liver is the largest organ in the body weighing between 1.36 and 1.81 kg (3 and 4 lb). It is only possible for the blood to get back to the heart and lungs from the stomach by first passing through a system of veins in the liver, known as the portal system.

A variety of things including viruses, drugs, environmental pollutants, genetic disorders and systemic diseases can affect the liver and stop it functioning properly. However, the liver has a marvelous capacity to renew itself and will usually return to normal once the causes are removed or eliminated.

Fact File:

If the kidneys do not work properly, they can become ‘furred’ up with hard crusts and crystals of chemicals from the urine. These deposits are called kidney stones. They can be removed by an operation, dissolved by drugs, or shattered into tiny fragments by high-energy ultrasonic sound waves.

 

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