Middle ear


The tympanic membrane serves as a segregating point between the middle ear and the external acoustic canal of the outer ear. This creates an air filled chamber known as the tympanic cavity, where the middle ear is is laterally compressed. It can be located in the petrous part of the temporal bone.


The middle ear and the inner ear are segregated by a bony structure known as the vestibular window and the cochlear window. The vestibular window is ovular while the cochlear window is circular. The tympanic cavity hosts two openings.

Connecting the tympanic cavity with the mastoidal air cells, which reside in the mastoid process of the temporal bone, is the epitympanic recess. In order to equalize the air pressure on both sides of the tympanic cavity, the Eustachian tube, also known as the auditory tube, serves as the connecting piece between the tympanic cavity and the nasopharnyx.

Reaching out across the tympanic cavity, there are three auditory ossicles which reach the vestibular window. These are the smallest bones within the human body. From smallest to largest these bones are named the malleus, the incus, and the stapes. Ligaments maintain the position these tiny bones hold within the structure of the ear.


Middle Ear
Image: Middle Ear

The tympanic membrane echoes the sound required to vibrate these tiny bones, which transmit sound waves detected via vibration of these bones. The sound waves carried on the vibrations reach the vestibular window. From the vestibular window, these vibrations reach a fluid filled cavity deep within the inner ear, stimulates the receptors, which transmits sound waves into the brain which is recognized as sound.

The ossicles serve as a systematic lever amplifier to deliver the necessary sound waves. The sound waves are once again subjected to amplification as they leave the larger tympanic cavity and enter the smaller vestibular window. This system allow for amplification of about 20 times the starting volume.


To guard the inner ear against volumes large enough to damage the inner ear, there are two tiny skeletal muscles known as tensor tympani muscle and the stapedius muscle, which can reflexively contract. As they are attached to the malleus and the stapes, these muscles can also help diminish loud sound and allow for smaller vibrations.

In order to offer protection, the tensor tympani contracts and the malleous is driven inward while the stapes is forced outward by the contraction of the stapedius muscle.
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