What is the middle ear?
The middle ear consists of a system of air-containing spaces that are lined with a thin and well-perfused mucous membrane: The middle ear cavity (tympanic cavity, cavitas tympanica or cavum tympani) contains the auditory ossicles hammer, anvil and stirrup. The cavity is connected to several air-filled (pneumatic) secondary spaces (cellulae mastoideae) and to the pharynx via the Eustachian tube (Eustachian tube, tuba eustachii).
The tympanic cavity
The tympanic cavity (middle ear cavity) is a gap-shaped space about 10 to 15 millimeters high and only about five millimeters wide, which has six walls. The lateral wall consists almost entirely of the eardrum, to which the head of the malleus is attached. The medial, inner wall separates the tympanic cavity from the inner ear. This is where the oval window is located, which accommodates the stapes plate.
The auditory ossicles
The hinged ossicles are located in the upper part of the tympanic cavity. You can find out more about them in the article Ossicles.
The pneumatic sinuses
The Eustachian tube
The Eustachian tube connects the tympanic cavity with the nasopharynx. You can read more about this in the article Eustachian tube.
The function of the middle ear
The middle ear acts as a sound bridge: It transmits the sound waves that hit the eardrum to the actual sensory-perceiving section of the ear – the cochlea. This takes place via the ossicular chain, which acts like a lever system: The vibrations of the large-area eardrum (large vibration amplitude, low force) are transmitted largely loss-free to the small-area oval window via the hammer, anvil and stirrup. The oval window is a delicate membrane that separates the air-filled middle ear from the fluid-filled inner ear. Due to the leverage effect of the auditory ossicles and the difference in size between the eardrum and the oval window, the sound is amplified by a factor of around 22. The sound is transmitted via the oval window to the fluid in the inner ear (perilymph) and on to the auditory sensory cells.
What problems can the middle ear cause?
Mastoiditis occurs when an inflammation of the middle ear spreads through the cavity system of the mastoid (mastoid process) and leads to inflammation or suppuration.
Middle ear diseases that impair the ability of the ossicles to vibrate lead to conductive hearing loss.
