Hearing the sound perception

Later in the course of evolution appeared the highest kinds of sensitivity - perception of sounds (hearing) and light (vision). Of exceptional importance of hearing and vision is that they have already published signal about these or those objects and phenomena of the surrounding environment. Therefore they are called in physiology distant analyzers. Higher chemical sensitivity - the sense of smell is also very much having the same property. However, special degree of development it is in the organs of hearing and sight.
Rumor has arisen on the basis of sensitivity to mechanical irritation. However, here are perceived not touch those or other subjects, and much more subtle effects of fluctuations in air. The perception of vibrations of air is essential.
All surrounding objects - solids, liquids, or gases have some elasticity. So when touching one body to another, and even more so when you blow them each other's body, these make a number of vibrational motion - simply put, shudder, shiver. In the nature there is no void. Therefore, every motion of one object causes its contact with the other items vibrate, and these vibrations are transmitted to the air. As a result we hear the sound of - motion information around us. Shaking whether the anvil under the blows of the hammer, varies water from a stone thrown into, trembling whether the vocal cords of a singer under the pressure of a jet of air, trembling whether pages of the book under perelistyvaem their hands - all this causes vibrations in the air, spreading around with the speed of 340 meters per second, or 1 km in 3 seconds, and we hear the sound. How is the perception of him?
Air oscillations affect thin, but elastic membrane, which abuts the ear canal; this membrane - eardrum. Its thickness of 0.1 mm From it through a chain of three tiny bones, reducing to 50 times the amplitude of oscillations, but in a 50-fold increase their strength, vibrations are transmitted to the liquid in the inner ear. Only here, in fact, starts the perception of sound. Because eardrum is only one link in the transmission of sound to the inner ear, the violation of her integrity does not lead to hearing loss, although, of course, reduces it.
The main part of the inner ear is the tube, twisted in the form of snails, and therefore called the cochlea. Between its walls tight-lipped about 24 thousand finest fibers, yarns, whose length from the tip of the cochlea to its base gradually decreases. This is our strings. If before the piano loudly pronounce some sounds, piano us will answer. If we said in a bass, the piano will answer a low sound. If we squeaked, and in response will hear high-pitched tone. This phenomenon is called resonance. Each string of a piano is tuned to the sound of a certain height, i.e. to fluctuate with some frequency (more than fluctuations, the more it seems to sound). If the string impact air waves of the same frequency, as is the frequency at which it is configured, string resonates, is responsible.
On the same principle based sound to our ears. In connection with different length fiver each is configured to a specific frequency vibrations - from 16 to 20 000 in the second. Long fibrils in the apex perceive vibrations of low frequency, i.e. low sounds, and short fibrils the base of the cochlea - frequent fluctuations. This was demonstrated by the student of I. P. Pavlov, thin experimenter L. A. Andreev. The method of conditional reflexes allowed finally learn to hear the animal certain sounds in the destruction of one or another part of the cochlea. It was found that if you destroy the dog upper part of the cochlea, then, no matter how many times before it is needed neither to give low sounds, conditioned reflex they are not formed. This undoubtedly proves that the animal now does not treat these sounds. This way was "felt" the number of departments of the cochlea. Only experiments L. A. Andreeva finally proved that really fibrils snails are our resonators. Nominated resonance theory of the hearing in the last century, famous Helmholtz not been able to prove it by experiment.
If the air varies more than 20,000 times per second, we have not perceived by the ear of these fluctuations. They are called ultrasounds. The dog, as shown by studies of conditioned reflexes, border hearing comes to 40 000 Hz. It means that the dog hears ultrasounds, inaccessible to man. This could be used, among other things, circus trainers for animal feed secret signals.