My Science School

 

 

The coccyx is the lower end of the spinal column of man and consists of four nodules of bone, like tiny vertebrae, corresponding to the tail, which is found in lower animals. The bones are deeply buried in muscle tissue, but occasionally they jut backwards and are surrounded by a fold of skin, so as to form an actual tail.

    The name coccyx was given by the Greek physician Galen (c. A.D. 130-200) and free comes from the Greek word for “cuckoo”, as the bone rather resembles a cuckoo’s bill.

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Cardiac pacemakers are used by sufferers from “heart-block”. They do the work normally performed by the body’s natural pacemaker in controlling the rate and rhythm of the heart beats. This natural pacemaker is a small collection of specialized nervous tissue situated at the base of the heart. It forms the starting point for the impulses that initiate the heartbeats.

    “Heart-block” is a serious condition in which the conducting mechanism between the cavities of the heart (atrium and ventricle) is impaired or destroyed. When this happens, the atrium and ventricle beat at different rates independently of each other because the impulse from the pacemaker is not reaching all parts of the heart. Fainting, convulsive attacks or complete stoppage of the heart may follow, but the condition can be overcome by the use of an artificial pacemaker.

      This acts as a battery to stimulate the heart, allowing it to beat regularly at normal speed, about 70-80 impulses a minute. The pacemaker is either fixed to the outside of the chest or implanted in the armpit and connected to an electrode tube, which is passed through the main vein in the neck into the heart.

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Muscles are the body tissue which, because it has the power of contraction, enables the higher animals to move their bodies. Muscles are divided into two great groups, voluntary and involuntary, the former being controlled by the will, while the latter act independently

     Most voluntary muscles are attached to the skeleton and range in size and shape to suit the particular jobs they perform. They can get into action within a few hundredths of a second, exert an enormous pull on the bone to which they are attached and, if necessary, support 1,000 times their own weight. Involuntary muscles include heart muscle and the muscles of the digestive system, and the fibers of which they are composed are very much smaller than those of voluntary muscle.

    Because of its exceptionally rich blood supply, muscle is the most infection-free of the body’s basic tissues. If it is over-taxed it tires and will stop contracting altogether, but if used normally will give little trouble.

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We take a grip on things by using our muscles to exploit the development of the human thumb. The importance of this thumb is that it can be moved across the palm of the hand to touch the index finger. In contrast the digits of a monkey’s hand are more rigid. This difference explains why a human being can handle an instrument with such precision.

     The mechanism of the hand is operated by way of the wrist, a hinge joint composed of eight small bones (carpals) packed firmly together to give elastic stability. Below the wrist project five small, long bones (metacarpals) which give the palm firmness. Four of the bones have hinge joints and are connected to the thumb allows it to move round and meet the fingers and palm, thus providing a firm grip.

    Possession of such a hand has enabled man to form a society and culture based on the use of tools. It is thought the hand developed from the five-rayed forepaw of an early vertebrate. However, occasionally a child is born with an extra tiny thumb or little finger and some people believe that the forepaw was originally seven-rayed.

    The human thumb has length longer in proportion than that of an ape. About 92% of human being is right handed, but apes tend to use both hands with equal ease.

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Inside the womb of a pregnant woman or animal a placenta is formed, through which the unborn baby is nourished. The baby is connected to the placenta by the umbilical cord, which is joined to the unborn child at the navel.

     The umbilical cord is the baby’s lifeline. Everything the child needs to survive will pass through it- air, blood and nourishment. At most it is no more than an inch wide and, perhaps, only a foot long.

    Once the baby is born the placenta, which serves a purpose only during the pregnancy, will be discarded.

      The umbilical cord will be cut with scissors a few inches away from the newborn baby’s stomach. This is quite painless because the umbilical cord has no nerves. The baby will now breathe on its own.

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The body temperature of a human being is an indication of his physical condition, so that an abnormally high or low temperature is generally a sign that something is wrong.

     The normal temperature is usually given as 36.90 C. (98.40 F.), but as the body temperature varies throughout the day, anything between approximately 36.70 C. (OR 98.10 f.) and 37.20 C. (or 99.00 F.) may be taken as normal.

    For instance, the temperature rises after a large meal, during hot weather and after violent exercise. Your temperature is at its lowest at night when you are asleep.

    Control of body temperature is exercised by a centre in the brain which ensures that a balance exists between heat production and heat loss. A raised temperature is often the sign of bacterial or virus infection. It may be due to heatstroke, to certain types of brain injury or disease or to shock.

     A very high temperature, or fever, may begin with a “rigor” (an attack of shivering and cold), in which the whole body may tremble uncontrollably and the teeth chatter. Although at this stage the skin feels cold and clammy, the temperature within the body is raised. Soon the skin becomes hot and dry, pulse and breathing rate are speeded up and there is a feeling of exhaustion, aching muscles. Headache, thirst and perhaps delirium and loss of the sense of time.

    Finally this stage is succeeded by profuse sweating and a gradual relief of the symptoms.

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The brain directs and coordinates movements and reflexes, registers sensations and is the supreme nervous organ by which man acquire knowledge and the power to use and adapt it. It shapes our personalities, and without it we would be more helpless than the tiniest human baby.

       There are three main parts of the brain: the forebrain (or cerebrum), the midbrain and the hindbrain. They have the consistency of soft jelly and are protected by three membranes (meanings), a tough outer envelope called the dura and a water fluid (cerebrospinal fluid) which acts as a support and a cushion. The brain is connected to the spinal cord, and its surface is highly convoluted.

      The cerebrum which forms nearly nine-tenths of the brain is divided into two halves (hemispheres). Generally the left half of the cerebrum controls the right half of the body, and the right half of the cerebrum controls the left half of the body. Some areas are connected with the special senses of man, but there are so-called “silent areas” which scientists believe are connected with memory and the association of ideas. The thalamus, a mass of grey matter which is buried in the cerebrum, is the source of instinctive feelings and emotion.

    The midbrain is concerned with eye-movements, while the hind-brain contains the nerve cells responsible for breathing, heart action, and digestive juices and so on. The cerebellum, a part of the hindbrain, plays an important role in the execution of the more highly skilled movements.

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