Category Zoology

When are twins conceived?

A baby begins as a fertilized egg – a pinhead-sized egg cell from the mother, which has joined an even smaller tadpole-shaped sperm cell from the father. Although thousands of these sperm cells may cluster around the egg cell, only one of these will actually fertilize the egg.

Non-identical twins are produced when two eggs are released at the same time, and both are fertilized. They can be the same sex, or brother and sister.

Identical twins are produced when the embryo splits into two in the early stages of its development. This produces two identical children of the same sex. Some identical twins look so alike that they can only be told apart by their fingerprints.

Only one in 83 pregnancies results in twins.

Fact File:

The bones of a baby’s head are not fully fused at birth, allowing the skull to pass through the mother’s birth canal. The bones gradually become joined, but a gap at the top of the skull, called the fontanelle, may not close up for several months. 

 

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When are babies delivered as a ‘Breech Birth’?

At about 280 days after the baby’s inception, the mother starts to feel strong tightening pains, called contractions, in her womb when the birth is near. These contractions become stronger and the neck of the cervix starts to open. As the contractions continue, the baby’s head moves down and eventually emerges through the cervix and vagina.

A breech birth is different to a regular birth because the buttocks engage in the pelvis instead of the head. This makes delivery more complicated as the largest part, namely the head, is delivered last. A breech birth is encountered about once in every thirty deliveries. Because the head in such cases is the last part of the child to be delivered and because this part of the delivery is the most difficult, the umbilical cord may be compressed while the after-coming head is being born, with the result that the child may be deprived of oxygen.

Fact File:

Sometimes a baby cannot be born normally through the vagina and so it has to be surgically removed from the mother’s womb. This operation is called a caesarean section.

 

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When do we use our brain to smell?

The part of the brain that analyzes messages coming from the receiver cells in the nose is closely connected with the limbic system, that part of the brain that deals with emotions, moods and memory. It is called the primitive brain, sometimes even the ‘smelling brain’. The connection explains why smells are richly supplied with emotional significance. The smell of fresh-baked bread may bring on instant pangs of hunger, while the scent of perfume may remind you of a loved one. On the other hand, unpleasant smells such as rotten eggs, produce revulsion and sometimes even nausea.

Certain smells will bring memories of long forgotten special occasions flooding back. This is because the areas of the brain which process memories are also closely linked to the limbic system, which in turn is linked to the areas in the brain that control the sense of smell.

Fact File:

Aromatherapy is the art of using the perfumed essential oils of plants to treat the body and mind. The perfume passes over the nerve cells in the nasal passage and a message is sent to the brain.

 

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When does our sense of touch alert the brain of danger?

Close your eyes and touch something, such as your clothes, a table, a car or even your own skin. Stroke it gently. What does it feel like? Is it hard or soft, hot or cold? The surface may be smooth, bumpy, gritty, furry or hairy. It could be dry, moist, or slimy. Your skin continuously passes huge amounts of information to the brain. It monitors touch, pain, temperature and other factors that tell the brain exactly how the body is being affected by the environment. Without this constant flow of information, you would keep injuring yourself accidentally, which is what happens in some rare diseases where the skin senses are lost. Senses in the skin are measured by tiny receptors at the ends of nerves. There are several different types of receptor. Each type can detect only one kind of sensation, such as pain, temperature, pressure, touch and so on.

Fact File:

Sometimes we need drugs, or analgesics, to control a pain. Some drugs, such as aspirin, work by preventing the sensation of pain from reaching the brain.

 

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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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