The Larynx and the Ear : Part 1

Physiology and Hygiene for Secondary Schools
by Francis M. Walters

(Page 21 of 27)

Man is a social being. His inclinations are not to live alone, but to be a part of that great human organization known as society. For men to work together, to be mutually helpful one to another, requires the ability to exchange ideas and this in turn requires some means of communication. One means of communication is found in certain movements of the atmosphere, known as sound waves. In the exchange of ideas by this means there are employed two of the most interesting divisions of the body - the larynx and the ear. The first is an instrument for the production of sound waves; the second is the sense organ which enables the sound waves to act as stimuli to the nervous system.

Nature of Sound Waves. - If some sonorous body, as a bell, be struck, it is given a quivering, or vibratory, motion. This is not confined to the bell, but is imparted to the air and other substances with which the bell comes in contact. These take up the movements and pass them to objects more remote, and they in turn give them to others, until a very considerable distance is reached. Such progressive vibrations are known as waves, and, since they act as stimuli to the organs of hearing, they are called sound waves. Sound waves always originate in vibrating bodies. They are transmitted chiefly by the air, which, because of its lightness, elasticity, and abundance, readily takes up the vibrations and spreads them in all directions.

While these vibratory movements of the atmosphere are correctly classified as waves, they bear little resemblance to the waves on water. Instead of being made of crests and troughs, as are the water waves, the sound waves consist of alternating successions of slightly condensed and rarefied layers of air. Then, while the general movement of the water waves is that of ever widening circles over a surface, the sound waves spread as enlarging spherical shells through the air. In sound waves, as in all other waves, however, it is only the form of the wave that moves forward. The individual particles of air that make up the wave simply vibrate back and forth.

How Sound Waves act as Stimuli. - Any sound wave represents a small but definite amount of energy, this being a part of the original force that acted on the vibrating body to set it in motion. The hammer, for instance, in striking a bell imparts to it a measurable quantity of energy, which the bell in turn imparts to the air. This energy is in the sound waves and is communicated to the bodies against which they strike. Though the force exerted by most sound waves is, indeed, very slight, it is sufficient to enable them to act as stimuli to the nervous system.

How Sounds Differ. - Three distinct effects are produced by sound waves upon the nerves of hearing, and through them upon the mind. These are known as pitch, intensity, and quality, and they are dependent upon the vibrations of the sound-producing bodies.

Pitch, which has reference to the height, or degree of sharpness, of tones, is determined by the rapidity of the vibrations of the vibrating body. The more rapid the vibrations, the higher the pitch, the number of vibrations doubling for each musical interval known as the octave.

Intensity is the energy, or force, of the sound waves. This is recognized by the strength of the sensation and is expressed by the term loudness. Intensity is governed mainly by the width of the vibrations of the vibrating body, and the width depends upon the force applied to the body to make it vibrate.

Quality is that peculiarity of sound that enables tones from different instruments to sound differently, although they may have the same pitch and intensity. Quality depends upon the fact that most tones are complex in nature and result from the blending together of simple tones of different pitch.

Reinforcement of Sound Waves. - The sound vibrations from small bodies are not infrequently reinforced by surrounding conditions so that their outgoing waves reach farther and are more effective than waves from larger bodies. This is true of the sound waves produced by most musical instruments and also those produced by the human larynx. Such reinforcement is effected in two general ways - by sounding boards and by enclosed columns of air. Stringed instruments - violin, guitar, piano, etc. - employ sounding boards, while wind instruments, as the flute, pipe organ, and the various kinds of horns, employ air columns for reinforcing their vibrations. In the use of the sounding board, the vibrations are communicated to a larger surface, and in the use of the air column the vibrations are communicated to the enclosed air.

Value of Sound Waves to the Body. - From a physiological standpoint, the value of sound waves is not easily overestimated. In addition to the use made of them in the communication of ideas, they serve the purpose of protecting the body, and in the sphere of music provide one of the most elevating forms of entertainment. Sounds from different animals, as well as from inanimate objects, may also be the means of supplying needed information. The existence of two kinds of sound instruments in the body - the one for the production, the other for the detection, of sound - is certainly suggestive of the ability of the body to adjust itself to, and to make use of, its physical environment. Both the larynx and the ear are constructed with special reference to the nature and properties of sound waves.

The Larynx

The Sound-producing Mechanism of the Body consists of the following parts:

1. Delicately arranged bodies that are easily set in vibration.

2. An arrangement for supplying the necessary force for making these bodies vibrate.

3. Contrivances for modifying the vibrating parts so as to produce changes in pitch and intensity.

4. Parts that reinforce the vibrations.

5. Organs by means of which the sounds are converted into the forms of speech.

D.C. Heath and Co. - Publishers
Original copyright 1909