Our body has five main sense organs
The world around us is very interesting. There are colourful sights to see, sweet sounds to hear, wonderful things to touch, fragrance to smell and delicious eatables to taste. Our body has five sense organs to help us do all these things. They enable us to detect what is happening in the outside world. How can we observe changes around us?
Sense organs carry messages about our surroundings to the brain. Do you know that the brain is the control room of our body?
Our eyes, ears, skin, nose and tongue are our senses. Here we discuss the structures and functions of these organs.
1:>EYE: SENSE OF SIGHT
We see beautiful objects of nature such as blue sky, high mountains, flowers, animals, other human beings and so many things with our eyes. So, our eyes give us our sense of sight. Have you ever been told to 'use your eyes' when you complain that you cannot find something or other?
Our eyes tell us about colour, shape, position and movement of objects around us.
The human eye consists of an eyeball which is well protected in a socket, called the orbit inside the skull bone.
The outsides of our eyes are covered by the upper and lower eyelids and eyelashes. Under the upper eyelids tear glands also open.
Our eye is made up of three layers.
1 . SCLEROTIC:
The outer tough, white and opaque layer is called sclerotic. In the front of eye, this layer becomes transparent and dome shaped and is called cornea. Light rays enter the eye through the cornea.
2 . CHOROID:
Beneath the sclera is the layer called choroid. It is black and light proof. In the front of eye, this layer forms the coloured portion of the eye called the iris. Have you ever observed brown, blue and hazel eyes of your friends? There is a hole in the middle of the iris, known as the pupil. This pupil contracts in flash or daylight and expands in dim light. Behind the pupil, a flexible and transparent lens is present. The lens focuses the light rays coming into the eye and forms the image. This lens can change its shape to see near and far objects.
3. RETINA:
The innermost and light sensitive layer of the eyeball is called the retina. Eye lens forms the image on the retina. The retina is made up of sensory cells, rods and conse.
When light hits the retina, its cells make nerve signals. These signals pass along the optic nerve to the brain.
SHAPE OF THE EYE
The shape of the eyeball is maintained by the clear jelly like fluid. It is aqueous humour between the lens and the cornea and vitreous humour between the lens and the retina.
2:> EAR: SENSE OF HEARING
The ear is another important sense organ of our body. We hear musical sounds with them, but sometimes we have to hear noise too. Our ears give us our sense of hearing. Without this sense, we cannot communicate with others. Young children learn to speak by listening to other people. Can you explain why is a deaf person also a dumb one? You have already learnt that sounds are produced by the vibration of objects. These vibrations produce sound waves in the air. Our ears receive these sound waves and send message to the brain.
The ear is composed of three parts which are as follows:
1:> Outer Ear
2:> Middle Ear
3:> Inner Ear
1. OUTER EAR:
The outer ear consists of a pinna and a long narrow tube called ear canal. The curly flap of skin and gristle on the side of the head is funnel shaped pinna. It collects the sound waves from the air around like the antenna of the television does. The sound waves then travel along a little curved tube, the ear canal.
2. MIDDLE EAR:
The outer ear is connected to the middle ear by a thin sheet of skin called the ear drum. This eardrum vibrates when sound waves strike on it. On the other side of the ear drum is the air filled chamber called the middle ear. It is composed of three smallest bones in the body. The first bone is the hammer which picks vibrations from the eardrum and passes them to the second bone, the anvil. Finally, the vibrations go to the third bone, stirrup. These bones are arranged in a lever-like manner and transfer the sound waves to the inner ear. The middle ear is also connected with the back of the throat through the eustachian tube.
3. INNER EAR:
The last part of the ear is shaped like a snail's shell. It is called the inner ear. The inner ear is filled with liquid. This part of ear has a coiled structure called cochlea. The cochlea is the actual hearing organ. There are many very tiny hair-like cells in the cochlea. The sound waves coming from the middle ear cause the liquid and hair-like cells to vibrate. These sensory cells send signals to the brain through a special nerve called auditory nerve. Our brain helps us understand the sound we hear. The inner ear also contains three semi-circular canals. A fluid is filled in these half circle canals that moves whenever your head changes position.
3:> SKIN: SENSE OF TOUCH
The largest sense organ in our body is the skin. Our skin gives us our sense of touch. It is an important sense too. We learn a great deal about our surroundings through this sense. By using our sense of touch, we can tell whether an object is hard or soft, rough or smooth, wet or dry, cold or hot. Even we feel pain and pressure using this sense.
skis the protective covering present on every part of our body. It has an outer layer and an inner layer. The outer layer which you see all the time is made up of thousands of dead cells. This layer normally, has no sensation at all. It only serves as a protective layer. This layer is called epidermis. The inner layer contains several blood vessels and nerves. This layer is the sensitive part of the skin. Is this layer alive or dead? When we touch something, sensitive cells of the skin receive messages and send them to the brain.
4:> Nose: SENSE OF SMELL
Suppose there is a dead and decaying rat in one of your room's corners. How would you come to know about the dead rat? Of course, you smelled bad odour in the room. The sense organ for smelling is the nose. Our nose gives us our sense of smell. We can smell different odours ‘ around us through this sense. It is also a very important sense. How do you get familiar about the food cooking in the kitchen, when you step in the kitchen?
Our nose is divided Into two nostrils. In each side of the nose is an air chamber
about as large as a thumb. The roof of the chamber has lining of nerve cells to sense smell. Each cell has tiny hairs sticking from it. When certain odour chemicals present in air enter our nose, they touch the hairs of nerve cells. The hairs pass on the message about the odour to the brain through the olfactory nerve. Our brain interprets the message and thus we recognize the odour as pleasant or unpleasant. How do you come to know that a rose flower releases pleasant odour while dead and decaying matter releases unpleasant odour?
5 :> TONGUE: SENSE OF TASTE
How do we come to know that a mango is sweet but lemon is sour? The things we eat may be sweet, salty, sour or bitter. We recognize these four tastes with the help of our tongue. Our tongue is the sense organ that gives us our sense of taste.
The upper surface of the tongue is covered with many pimple like lumps called papillae. Between the papillae, taste buds are scattered. Each taste bud has many taste cells and nerve endings. When substances of a certain flavour foods touch the taste buds, they generate nerve signals. These signals are sent to the brain. We feel sweet, salty, sour and bitter tastes on different parts our tongue the tip of sides of the tongue are sensitive to salty and sour tastes. The back of the tongue can detect bitter taste. There are different taste buds to detect different taste.
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