There are many reasons for headaches. It is, however, believed that we feel the ache when pain signals are sent to the brain by nerves in the face, neck and the back. They arise out of a common root called the cranial nerve. That is why any factor which causes stimulation of pain nerves in and around the face is felt as a headache. We get headaches when the muscles in our eyes get strained, like when we read very small print or read for very long hours, or if our eyes have some defect such as a squint. Headaches can also occur when the tiny bones in the inner ear which pick out the sound for us to hear get tired or if our neck muscles get strained. There is one form of headache called migraine which periodically occurs in some persons for no apparent reason. Migraine can be triggered by many factors such as eating ice creams or fatty foods, cold, dehydration or allergies to certain food items. Aching teeth and sores in the mouth can also induce a headache.

            Blinking helps to keep the eye lubricated and also to sweep away foreign particles. Lubrication helps maintain the transparency of the cornea – the transparent outer layer in front of the eyeball. Along the edge of each eyelid are tiny glands that release a watery fluid each time the eyelid closes. Each time one blinks, the tear glands also release some fluids. The fluids flush out the eye and also keep it moist. A sudden movement in front of the eye also makes one blink. This has protective value. It has been estimated that an average person blinks about 250 million times in a lifetime.

Both, men and women may be affected equally by temporary hair loss due to stress, skin infection, disease, drug or radiation-induced side effects. Permanent baldness, seen mostly in men, is genetically governed. The gene for baldness is present on the X-chromosome. However, it does not express itself if a normal version is present on the partner chromosome. Since women have two X-chromosomes and men only one, a woman may carry a copy of the baldness gene on one X-chromosome with the other X-chromosome being normal. In such a case, the woman will not go bald. However, a copy of the baldness gene on the single X-chromosome of men predisposes them to the trait. It is unlikely (though not impossible) for a woman to carry copies of the baldness gene on both X-chromosomes. The tradition of keeping long hair allows women to cover patches of baldness better than men in whom the baldness shows.

 Body temperature can be measured by placing the thermometer under the tongue, in the armpits or in the rectum. The basic idea is to place the heat sensitive bulb of the thermometer in close contact with that part of the body which is not exposed as that may lower the reading. It is also desirable that the thermometer be enclosed on all sides by the body part. The armpits are easily accessible and the fear of broken thermometers is also less. So this is the preferred site for measuring temperature in children. For adults, the underside of the tongue is preferred, as the skin is very delicate                                                                                            here, heat conduction is better and the thermometer                                                                                           reading is more accurate.

 When one is hit, the force of impact damages the capillaries or the small blood vessels under the skin although the skin may remain unbroken. When a capillary breaks under the skin, blood oozes out and this internal bleeding gives skin its dark colour. Immediately after the injury the colour is red because of the presence of red blood cells. Gradually these cells dry and start losing oxygen and give the bruise a bluish colour. The thickness of the skin also distorts colour. A bruise may change from reddish blue to greenish blue and then yellow before fading completely.

            The red pigment of blood – haemoglobin serves two purposes; it carries carbon dioxide from body tissues to the lungs where it gives out carbon dioxide and takes up oxygen. Secondly, it carries the oxygen to various body tissues. Veins carry deoxygenated blood which has given up the oxygen. Deoxygenated blood appears slightly blue-red or purplish in colour. Since veins are thin walled and are usually located near the surface, they are visible through the skin and the deoxygenated blood coursing through them gives them bluish colour.

            About 60 per cent of our weight is water. Water is constantly lost from our body through exhalation, perspiration and urine. At the same time we obtain a good amount of water from our food, but it is not enough to keep the balance of water our body needs. That is why we need to drink water from time to time. When the water balance is disturbed, either due to excessive loss by perspiration or due to insufficient intake, the salt content of the blood changes. This change activates the thirst centre in our brain which                                                                                           makes us feel thirsty.

Have you noticed that when someone is nervous, he bites his nails or that a person looks down when he feels sad? Well, even though these people are not saying anything, their bodies are telling us how they feel. This type of communication in which our body movements, gestures and facial expressions reveal our feelings and personality is called body language.

            Body language is a form of soundless communication, or silent speech. Animals cannot speak, so they depend a lot on body language. An arch its back, while a happy dog will wag its tail.

            Human beings ‘speak’ three times more through their body language than through actual speech. Some forms of body language are the same throughout the world. Others change from place to place. In fact gestures that are considered to be polite in one country may be thought to be very rude in another!

Da Vinci code

            The artist and scientist Leonardo Da Vinci made thousands of drawings and observations in his notebooks, but his notes appear to be made in a secret code. Leonardo was left handed and his writing goes from right to left. It can be read properly if held up in front of a mirror!

    Normally when images of an object are formed on the retina of the two eyes, the two fields of vision overlap to some extent at the centre and provide a perception of depth. But for aiming at a distant object, depth perception is not as important as the proper line of alignment. For arches and shooters, the main objective is to find the line of alignment of the target and not its depth because the distance of the target is usually known. Since our two eyes are separated by a distance, they give two separate lines of alignment which can never allow the archer to aim exactly at the target. But on closing one eye, the archer can aim at the                                                                                    target more precisely by aligning his eye with the tip of                                                                               the arrow or gun sight and the target and shoot accurately.