The middle ear is the air-filled cavity behind the eardrum. The middle ear serves to 1) equalise pressure differences, 2) process and transmit the sound signal from the eardrum and 3) protect the inner ear.
|
 |
 |
Equalisation of pressure differences |
The Eustachian tube, which connects the middle ear to the nose and throat, ensures a neutral air pressure in the middle ear. This means that any difference between the pressure in the middle ear and the atmosphere is equalised.
Processing and transmission of sound |
The middle ear cavity houses three small bones: The hammer, the anvil and the stirrup. This chain of bones forms a lever mechanism which conducts the vibrations from the ear canal and eardrum to the inner ear fluid.
The middle ear with the eardrum (tympanic membrane), the hammer (malleus), anvil (incus) and stirrup (stapes).
Protection of the inner ear |
Two small muscles, the stapedius and the tensor tympani, are attached to the bones. These muscles are activated by a reflex when loud sounds reach the ear. When activated, they will impede the transmission of sound through the middle ear and thereby protect the inner ear.
The activity of the middle ear muscles is controlled by the acoustic reflex and can be monitored by impedance audiometry (see Hearing test in the encyclopedia).
Problems with the middle ear (for example infection) can lead to a conductive hearing loss which is typically temporary and can be diagnosed by impedance audiometry.
A conductive hearing loss is located in the outer parts of the ear and is, in many cases, caused by accumulated ear wax or fluid in the middle ear. A conductive hearing loss is often temporary and can typically be treated with antibiotics or surgery (e.g. drain).
SEE ALSO
Middle ear infectionConductive hearing lossHearing test
