The eye

The eye is basically a mechanism for receiving light and transforming it into electrical energy. The receptors in the eye transform it into electrical signals, which are passed on to the brain. The eye has a lot of components. The cornea and lens at the front of the eye focus the light into a sharp image on the back of the eye, the retina. The retina is made up of rods and cones.

Rods are highly sensitive to light and allow us to see under low levels of illumination. However, they are unable to resolve fine detail and are subject to saturation. This is the reason for the temporary blindness that is caused when we move from a dark room into sunlight. There are approximately 120 million rods per eye which are mainly situated towards the edges of the retina.

Cones are less sensitive to light than rods and can tolerate more light. There are three types of cones, each of which is sensitive to a different wavelength of light. These cones which number about 6 million are mainly concentrated on the fovea, a small area of the retina on which images are formed.

The human ear

The human ear has three main sections, which consist of the outer ear, the middle ear, and the inner ear. Sound waves enter your outer ear and travel through your ear canal to the middle ear. The ear canal channels the waves to your eardrum, a thin, sensitive membrane stretched tightly over the entrance to your middle ear. The waves cause your eardrum to vibrate. It passes these vibrations on to the hammer, one of three tiny bones in your ear. The hammer vibrating causes the anvil, the small bone touching the hammer, to vibrate. The anvil passes these vibrations to the stirrup, another small bone which touches the anvil. From the stirrup, the vibrations pass into the inner ear. The stirrup touches a liquid filled sack and the vibrations travel into the cochlea, which is shaped like a shell. Inside the cochlea, there are hundreds of special cells attached to nerve fibers, which can transmit information to the brain. The brain processes the information from the ear and lets us distinguish between different types of sounds.

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