tailieunhanh - ANATOMY, PHYSIOLOGY, AND DISORDERS OF THE AUDITORY SYSTEM - PART 2

Âm thanh bình thường đến các ốc tai qua ống tai và tai giữa, nhưng nó cũng có thể đạt được ốc tai thông qua xương dẫn. Âm thanh đi vào khoang tai giữa cũng có thể thiết lập các màng tympanic trong chuyển động và do đó đến ốc tai. 2. Áp lực âm thanh ở màng tympanic phụ thuộc vào các đặc tính âm học của Pinna, tai kênh, | CHAPTER 2 Sound Conduction to the Cochlea 1. ABSTRACT 1. Sound normally reaches the cochlea via the ear canal and the middle ear but it may also reach the cochlea through bone conduction. Sound that enters the middle-ear cavities can also set the tympanic membrane in motion and thereby reach the cochlea. 2. The sound pressure at the tympanic membrane depends on the acoustic properties of the pinna ear canal and the head. 3. The ear canal acts as a resonator which causes the sound pressure at the tympanic membrane to be higher than it is at the entrance of the ear canal. The gain is largest near 3 kHz the resonance frequency where it is approximately 10 dB. 4. In a free sound field the head causes the sound pressure at the entrance of the ear canal to be different mostly higher than it is when measured at the place of the head without the person being present. 5. The effect of the head on the sound pressure at the entrance of the ear canal depends on the frequency of the sound and on the angle of incidence of the sound direction to the sound source . 6. The difference in time of arrival of a sound at the two ears is the physical basis for directional hearing in the horizontal plane together with the difference in intensity of the sound at the two ears. 7. The middle ear acts as an impedance transformer that matches the high HEARING ANATOMY PHYSIOLOGY --- AND DISORDERS OF THE AUDITORY SYSTEM Second Edition impedance of the cochlea to the low impedance of air. 8. The gain of the middle ear is frequency dependent and the increase in sound transmission to the cochlear fluid due to improvement in impedance matching is approximately 30 dB in the mid-frequency range. 9. It is the difference between the force that acts on the two windows of the cochlea that sets the cochlear fluid into motion. Normally the force on the oval window is much larger than that acting on the round window because of the gain of the middle ear. 10. The ear s acoustic impedance is a measure of the .