Category Biology

 Skin colour is due to the dark pigment melanin which is produced by pigment cells in the lowest layer of the skin. There is the same number of pigment producing cells in the skin of all races but the amount of melanin produced varies. In dark-skinned people of tropical regions, there is more melanin because intensity of the ultraviolet radiation from the sun is stronger in the tropics. The extra melanin protects the skin from the harmful effects of ultraviolet radiation. In people living in the higher latitudes, the skin colour is lighter as they have less pigment. The lighter skin also helps in the production of vitamin D in the body under the low intensity of sunlight available. Other factors contributing to skin colour are the blood  in the blood vessels of the skin and the natural yellowish tinge of the skin tissue.

Tanning is a sort of natural protection mechanism provided by nature to the human skin. It involves an increase in the production of the pigment melanin which helps protect the skin against the dangerous effects of too much ultraviolet radiation from the sun.

The outermost layer of the skin contains cells called melanocytes that produce the pigment melanin. When the skin is exposed to the sun, the melanocytes get stimulated by the ultraviolet rays and produce more of melanin. This acts as a filter to block ultraviolet rays from penetrating the skin. The increased production of the brown-coloured melanin gives a darker colour to the skin, which appears as suntan.

The two eyes working together enable us to perceive depth which is not possible to do with only one eye. Our two eyes view an object from approximately the same height but they see the object from slightly different horizontal angles. When processed by the brain these two slightly different images gives rise to perception of depth and make the object appear in three dimensions. This ability, called stereoscopic vision, also allows us to judge distances, to estimate how far an object is, which is essential to enable us to go about in our daily chores.

Of all the ways we communicate with people, eye contact is the most powerful. Eye contact can be a loving gaze, a hostile stare, a nervous glance, or a refusal to look at a person Looking at a people and meeting their eyes are the first steps toward striking up friendships and making a good impression. But if you look at a person for too long, he or she may feel threatened.

            Failing to look at others causes suspicion as they wonder whether you are hiding something. Refusing to make eye contact also sends messages of arrogance, for it may convey that you do not consider the other person important.

            There are subtle, silent rules to eye contact and they vary from culture to culture. Most Asians prefer minimal eye contact whereas in America, the UK and most of Northern Europe moderate eye contact is preferred. The Hispanic cultures, along with cultures in the Middle East prefer very direct eye. So if you travel to another country, be sure to know what form of eye contact they are comfortable with, so that you don’t offend anyone!

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.