15.3 Receptors in man
Receptors are the sensory organs which receives a stimulus. Following are the main receptor organs in man.
- Organ of sight (eyes)
- Organ of hearing (eyes)
- Organ of smell (nose)
- Organs of taste (taste buds on tongue)
- Organ of touch (skin)
Eyes are the most marvelous of the sense organs as they make us aware of various objects around us, nearby and far away. When we see a tree we do not have to touch it or climb its branches in order to know what it is like. With normal vision we can reach out as far as out eyes can see and are thus become aware of events and circumstances around us. The eyes are organs of sight enabling to appreciate shape, color and movements of objects and persons around us.
Structure of the eye
In order to know how the eyes make us to see things we have to know how an eye is constructed. It is a relatively small organ, spherical in shape except in the front portion (the transparent region) where it bulges out a little. In the average person the eye is less than one inch (about 2.4 cm) in diameter each eye is located in a bony socket called orbit. The orbit is formed partly by the bones that surround brain and partly by the bones of upper face. The sockets also contain muscles that move the eye ball, the nerves and blood vessels that supply the eye balls. In front of each eye are eye-lids, an upper and a lower, which acting together act as a curtain to shut out light. As lids separate or when the eyes open the front portion of the eye ball is exposed and light can enter. Image is formed by the light rays entering the eye through the anterior transparent portion.
An eye has the following parts.
- Cornea 2. Iris 3. Lense
4. Sclerotic layer 5. Choroid layer 6. Retina
7. Blind spot 8. Aqueous chamber and aqueous humour
9. Vitreous chamber and vitreous humour
A camera which is a human invention is based on the same principle as the human eye.
Fig. 15.5 structure of eye
The sclerotic of eye ball is the out-most layer, white in color and is thick and firm. It is transparent in front and bulges out slightly to form the cornea. Below sclerotic is the second layer of the eye ball called choroid, which is pigmented and vascular. Behind cornea the choroids bends inwards to form the iris having a circular opening called pupil through which the size of pupil can be increased or decreased. Situated behind pupil is a biconvex lens, which undergoes changes in convexity during the process of focusing. It is kept in place by suspensory ligaments and muscles.
Category: 9th 10th