Ear is a highly developed and sensitive human sensory organ. Its main function is to sense and distinguish sound through energy conversion. Another important function is to maintain balance.
The best way to describe the function of the ear is to describe the way in which sound waves enter the ear. The ear can be divided into three parts: the outer ear, the middle ear and the inner ear.
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External ear: external ear includes auricle and external auditory canal
The only visible part of the ear structure is the pinna, which has a special spiral structure and is the first to respond to sound. The auricle acts like a funnel, which is more conducive to the introduction of sound into the ear. If there is no such funnel shape, the sound wave can enter the listening channel in a more direct way. However, such a spiral structure will lose part of the sound energy, and ultimately make it more difficult to hear and understand the sound content. The importance of auricle lies in the pressure difference between the inner ear and the outer ear. The air resistance in the ear is greater than that outside the ear because the air in the ear is compressed.
In order for sound waves to enter the ear in the best way, the resistance should not be too high, and the auricle just helps to overcome the pressure difference between the ear and the ear. The result is that the transmission process is more stable and more sound can be transmitted into the external auditory canal. The sound waves pass through the auricle, through the external auditory canal of 2-3cm, and then vibrate the tympanic membrane.
The middle ear is composed of tympanic membrane, auditory ossicle and eustachian tube. The tympanic membrane is the lateral wall of the middle ear. It is tapered and translucent towards the inner ear, separating the middle ear cavity or tympanum from the external auditory canal. The auditory ossicle is composed of malleus, incus and stapes, with a total weight of about 0.05g. The eustachian tube connects the middle ear cavity and the eustachian cavity. The middle ear can transform energy and enlarge sound energy.
Conversion of energy: the middle ear converts the sound energy from the external auditory canal into mechanical energy, which is transmitted by sound and air conduction to the auditory canal, vibrates the eardrum and makes the malleus handle attached to the eardrum act, and transmits the vibration to the auditory ossicle. At this time, the middle ear has made the energy conversion from sound energy to mechanical energy; later, due to the rotation of the stapes floor, vibrates the oval window, which stimulates the fluctuation of lymph Another conversion of mechanical energy to liquid energy was carried out.
Expand sound energy: the anatomical area of tympanic membrane is about 83mm2, the effective vibration area is 55mm2, which is 17 times larger than the area at the bottom of stapes (3.2mm2), that is to say, the sound pressure transmitted from tympanic membrane to stapes floor can be increased by 17 times; in addition to the leverage of auditory ossicles, the sound can be increased by 1.3 times, of course, the cone of tympanic membrane can also increase the force of sound wave on stapes floor, therefore, it can be improved The rise is 17 × 1.3 = 22.1 times, equivalent to the sound intensity of 27db.
The inner ear consists of vestibule, semicircular canal and cochlea. Vestibule and semicircular canal also complete balance function together with vision and body sense. The sound is transmitted to the inner ear, causing the fluctuation of the inner and outer lymph, and then causes the shearing movement of the cilia to form a transmission signal, which is finally transmitted to the auditory center of the cerebral cortex. This is the main pathological site of sensorineural deafness.
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