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Hearing impairment refers to partial or total loss of hearing. There are three types of hearing loss: conductive hearing loss, which occurs when there’s an obstruction of sound wave transmission; sensorineural hearing loss which occurs when the inner ear or auditory nerve is damaged; and mixed hearing loss which is a combination of the two.
Let’s start with the normal physiology of hearing. The ear is made up of three parts: the external, middle, and inner ear, all of which help process air vibrations as sound. The main role of the external and middle ear is to transfer and amplify sound, while the inner ear also plays a role in balance. Let’s start with the external ear, which is by far the most common anatomical spot to hang earrings from. The external ear is actually a complex structure made of the auricle, also called the pinna; and the external acoustic meatus. Now, at the end of the external acoustic meatus, there’s the thin, oval tympanic membrane, more commonly known as the eardrum, which separates the external ear from the middle ear. When sound waves hit the tympanic membrane, it vibrates and transfers the vibration to the middle ear.
The middle ear, also called the tympanic cavity, is a tiny chamber found in the petrous part of the temporal bone, and it houses the three auditory ossicles, called the malleus, incus and stapes, which are the three smallest bones in the body. These ossicles create a chain that connects the tympanic membrane to the oval window to transfer and amplify air vibrations into the inner ear to be processed as sound. Now, the inner ear contains the bony labyrinth, which contains cavities filled with perilymph, and the membranous labyrinth, which is made of sacs and ducts suspended in the bony labyrinth.
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