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Bill Rustom Cruz January 7, 2011

BSECE

5 SENSES OF THE HUMAN BODY

Sense of Smell  –

 Smell, one of the five special senses (see Sense Organs) by which odors are

perceived. The nose, equipped with olfactory nerves, is the special organ of smell. The olfactory

nerves also account for differing tastes of substances taken into the mouth, that is, most

sensations that appear introspectively as tastes are really smells.

Sensations of smell are difficult to describe and classify, but useful categorizations have

been made by noting the chemical elements of odorous substances. Research has pointed to the

existence of seven primary odors — camphorlike, musky, floral, peppermintlike, ethereal (dry-

cleaning fluid, for example), pungent (vinegarlike), and putrid — corresponding to the seven types

of smell receptors in the olfactory-cell hairs. Olfactory research also indicates that substances

with similar odors have molecules of similar shape. Recent studies suggest that the shape of anodor-causing chemical molecule determines the nature of the odor of that molecule or substance.

These molecules are believed to combine with specific cells in the nose or with chemicals within

those cells. This process is the first step in a series that continues with the transmission of 

impulses by the olfactory nerve and ends with the perception of odor by the brain.

Sense of Hearing - Hearing (sense), one of the five main senses, by which sound waves are

perceived by the organ of hearing — the ear — in vertebrate animals. The process of sound

perception is called audition. The physical stimulus of auditory sensation is the vibration of some

material object. The vibration is transmitted from the object to the ear, under ordinary conditions,

by a wave movement of air particles.

Sense of Touch - one of the five senses (see Sense Organs) in humans and other animals, by

which the body perceives contact with substances. In humans, touch is accomplished by nerve

endings in the skin that convey sensations to the brain via nerve fibers. Nerves end in or between

the cells of the epidermis, the outer layer of the skin, in all parts of the body. In one complex

form of nerve ending, the terminals form tiny swellings, or end bulbs; characteristic of this form

are the Pacinian corpuscles found in the sensitive pad of each finger. Touch is the least

specialized of the senses, but acuteness can be sharpened by use; for example, people who are

blind exhibit a remarkable delicacy of the tactile sense in their ability to read the fine, raised

letters of the Braille system.

Sense of Taste - one of the five special senses (see Sense Organs), in humans and other animals,by which four gustatory qualities (sweetness, sourness, saltiness, and bitterness) of a substance

are distinguished. Taste is determined by receptors, called taste buds, the number and shape of 

which may vary greatly between one person and another. In general, women have more taste

buds than men. A greater number of taste buds appears to endow a greater sensitivity to

sweetness, sourness, saltiness, and bitterness. In humans, the taste buds are located on the surface

and sides of the tongue, the roof of the mouth, and the entrance to the pharynx. The mucous

membrane lining these areas is invested with tiny projections of papillae, each of which in turn is

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invested with 200 to 300 taste buds. The papillae located at the back of the tongue, and called

circumvallate, are arranged to form a V with the angle pointing backward; they transmit the

sensation of bitterness. Those at the tip of the tongue transmit sweetness, whereas saltiness and

sourness are transmitted from the papillae on the sides of the tongue. Each flask-shaped taste bud

contains an opening at its base through which nerve fibers enter. These fibers transmit impulses

directly to the brain. In order for a substance to stimulate these impulses, however, it must be in

solution, moistened by the salivary glands. Sensations of taste have been determined to be

strongly interrelated with sensations of smell.

Sense of Sight - Vision, ability to see the features of objects we look at, such as color, shape,

size, details, depth, and contrast. Vision is achieved when the eyes and brain work together to

form pictures of the world around us. Vision begins with light rays bouncing off the surface of 

objects. These reflected light rays enter the eye and are transformed into electrical signals.

Millions of signals per second leave the eye via the optic nerve and travel to the visual area of 

the brain. Brain cells then decode the signals into images, providing us with sight.

Almost all animals respond to light. The one-celled amoeba responds to light by turning in its

direction. Bees have complicated eyes that contain many lenses for sensing colors and shapes of 

flowers. However, it is the vertebrates (animals with backbones) that have eyes and a brain that

work together to process light into true images. Human vision is particularly unique in that the

human brain can process visual images and use them to create language and pictures and to store

information for future use.

The eyes of many vertebrates are specialized for certain situations. Bats see best at night. Birds

of prey, such as hawks and eagles, are able to see extremely small details, such as tiny rodents

viewed from high in the air.