About Hearing

The ear is a sophisticated organ that transmits the sounds we hear into electrical impulses that are interpreted by the brain. The process of hearing and interpreting sound is accomplished at a fantastic speed. To achieve this remarkable feat, each part of the ear - outer, middle and inner ear - fulfills a specific function.

Outer ear



The outer ear is composed of the pinna, the familiar visible portion of the ear, and the ear canal. The shape of the outer ear serves to give preference to sounds originating from the front. The shape of the ear canal serves to enhance frequencies that are important for hearing speech.

Middle ear



The middle ear consists of the eardrum, or tympanic membrane, and three tiny ear bones, or ossicles. The ossicles are the smallest bones in the human body. Although named the malleus, incus and stapes, they are often referred to as the hammer, anvil and stirrup because of their characteristic shape. Besides their role in the transmission of sound, these bones help to protect the ear from damage by constricting and limiting sound transmission when sound is too loud. The middle ear also contains the Eustachian tube, which connects with the throat, and serves to ventilate and regulate pressure in the middle ear.

Inner ear



The inner ear is composed of the semi-circular canals, which are important for balance, and the fluid-filled, snail-shaped hearing organ, the cochlea.

How we Hear/Transmission of Sound



The funnel shaped outer ear functions to collect sound waves which are then transferred through the ear canal to the eardrum.

Sound waves cause the eardrum to vibrate. This vibration stimulates the movement of the middle ear bones, which are attached to the eardrum on the middle ear side. These bones amplify the vibrations received by the eardrum and transmit them to the oval window, a small membrane on the cochlea, which separates the middle ear from the inner ear.

On the cochlear side of the oval window is fluid (or lymph) which fills the cochlea. Vibration of the oval window causes pressure waves within the cochlear fluid. The pressure waves stimulate movement of thousands of acoustic hair cells in the cochlea, converting the sound signal into electrical stimuli via neurons. These electric stimuli are transmitted to the brain via the eighth cranial nerve, or auditory nerve. In the brain these stimuli are processed and are perceived as sound.

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