Video about Hearing and How it Works | MED-EL

Ears are constantly active. They pick up sound waves and change them into information that the brain can interpret, such as music or speech. Sound is a pressure wave that can vibrate either quickly or slowly. Slow vibrations produce deep sounds while quick vibrations produce high-pitched sounds. Sound enters the ear and is directed through the ear canal where it first reaches the ear drum. As the ear drum begins to vibrate, it sets the ossicular chain in motion. The ossicular chain consists of the hammer, anvil and the stirrup. Sound vibrations move along the ossicular chain and into the inner ear. Within the inner ear, the cochlea plays a central role. It is here that the mechanical energy of sound is converted into complex electrical signals which are then passed on to the brain. In simplified terms, the cochlea is a spiral-shaped tube filled with fluid. Sensory cells, also called “hair cells”, line the entire length of the cochlea. These hair cells have varying degrees of sensitivity for the detection of different tones or frequencies. This allows the ear to perceive the entire spectrum of sound. The change from mechanical vibration to electrical pulse is a complex process resulting from the movement of hair cells in the cochlea. Along the entire length of the cochlea, the hair cells are arranged like the keys of a piano. Hair cells located at the base, or lower region of the cochlea, are responsible for high frequencies while hair cells at the apex are responsible for the low frequencies. As fluid in the cochlea is set in motion, it causes a corresponding movement of the fine structures on the surface of the hair cells to take place. These movements cause tension differences which produce electrical signals that are passed along the hearing nerve to the brain. The auditory cortex of the brain interprets this information as sound, for example as music or speech. The entire chain of events— including the various steps that convert sound waves from the environment into information that the brain can interpret— happens so fast that individuals can hear sound both continuously and instantaneously. Within this complex chain of events, there are a number of factors which can cause an individual to experience hearing loss. A loss of hearing can range from a mild to moderate hearing deficiency to a total hearing loss. In general, there are three main types of hearing loss which differ from one another depending on the part of the ear that is affected. Be it the outer, middle, or inner ear.


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