Our Five Senses

We have 5 senses that we use in many ways.

In the eye, the light goes through the cornea and across the aqueous humor, which is liquid. The light goes through the pupil, which is just space. How much light enters the pupil is controlled by the iris. When there is bright light, the iris contracts, making the pupil smaller. When there is darkness, the iris loosens, making the pupil larger. The light goes through the lens, which bends and focuses the light. Then, the light passes through the vitreous humor or "eye jelly." The light appears on the retina which has photoreceptors. The photoreceptors then send the message to the optic nerve, which goes to the brain.

Myopia
Myopia is the medical term for "nearsightedness", a condition wherein the eyes can see close objects but are unable to see distant objects clearly. Compared to the normal eye, a myopic eye is longer from front to back. As a result, light is focused in front of the retina, rather than on the retina, resulting in the perception of a blurred image.

Hyperopia
Hyperopia is the medical term for "far-sightedness." It is a misnomer, however, in that people do not necessarily see clearly only for far. As opposed to myopia, a hyperopic eye is shorter when compared to a normal eye. This results in light being focused behind the retina causing the perception of a blurred image.

Astigmatism
In order to have normal undistorted vision, the cornea should be smooth and spherical or equally curved in all meridians. Instead of being shaped like a basketball, the astigmatic eye is shaped more like an American football. Therefore, there is distortion or tilting of the images due to asymmetric bending of the light rays. This is sometimes perceived by the individual as a "shadow effect" or a doubling of the image.

In the ear, the noise is funnelled by the auricle into the ear canal. At the end of the ear canal is the ear drum that the sound waves vibrate. The vibrations from the ear drum vibrate three bones: the hammer, the anvil, and the stirrup. The stirrup vibrates the membrane of the inner ear. The inner ear contains fluid. The vibrations go through the fluid and into the cochlea. From the cochlea the vibrations go into the optic nerve where they are sent to the brain.

Sound can not travel through a vacuum, but must travel through matter. The more dense the matter, the more efficiently sound can travel. Sound travels through gases at a rate of 340 meters per second. It travels faster through liquids than gases and travels the fastest through solids. Sound cannot travel in space because there is no matter to carry the vibrations.

Smell is the most direct of our senses. Molecules float back into the nasal cavity behind the bridge of the nose where they are detected by receptor cells. Five million of these cells fire impulses to the brain's olfactory bulb or smell center. Such cells are unique to the nose. If you damage neurons (nerve endings) in your eyes or ears, both organs will be irreparably damaged, but the neurons in the nose are replaced about every thirty days.

Smell is stored almost exclusively in the long-term memory. Smells stimulate learning and information. Edwin T. Morris noted that a list of words was recalled much more easily and retained better when olfactory information was given along with a word list.
Like primary colors or the four basic tastes, all smells fall into a few basic categories: minty (peppermint), floral (roses), ethereal (pears), musky (musk), resinous (camphor), foul (rotten eggs), and acrid (vinegar).

Only substances volatile enough to spray microscopic particles into the air have a smell. When you smell chocolate chip cookies, you are actually smelling molecules of the cookie that have evaporated. Each person has an odor as individual as a fingerprint. In the absence of gravity, molecules will not float away easily, so the sense of smell is less effective.

The skin is the largest organ of the body. It weighs about six to ten pounds and is structured in two layers: the epidermis, or outer layer, and the dermis, or underlayer. The epidermis is the thin, scaly outer layer of the body that protects us from the outside environment. The top layer of the epidermis is made up of dead skin cells that are easily shed. The dermis protects and cushions the body. It houses hair follicles, nerve endings, sweat glands, blood, and lymph vessels. Specialized skin cells make up claws, spines, hooves, feathers, scales, and hair.

Three types of touch receptors sense pressure, pain, and temperature. The concentration of these receptors vary over the surface of the body. The fingertips, tongue, and lips are the most sensitive areas of the body because they contain the greatest concentration of nerve endings.

The versatility of touch allows us to explore the textures of the objects around us. It alerts us to danger. Studies have shown that touch plays a crucial role in child development. Babies and children who are not touched, stroked, kissed, held, and cuddled are less healthy - emotionally, mentally, and physically - than children who are touched. Touch is the key to our survival.

Just as we can smell something only when it begins to evaporate, we can taste something only when it begins to dissolve. Taste buds got their name from the nineteenth century German scientists George Meissner and Rudolph Wagner, who discovered mounds of taste cells that overlap like petals. Adults have about 10,000 taste buds grouped at various sites in the mouth. Inside each taste bud, about 50 taste cells relay information to the brain. We taste sweet things; we taste bitter things at the back; sour things are tasted at the sides; and salty things are tasted over the surface. Few taste buds are located in the center of the tongue, but there are incidental taste buds on the palate, pharynx, and tonsils. Taste buds wear out every week to ten days and we replace them, although not as frequently over the age of forty-five. Our sense of taste is not as sharp as we get older.

source: http://www.eyecenter.com.ph; http://www.uen.org/utahlink/lp_res/TRB028.html