The tympanic cavity, or middle ear, of the human auditory system is a compressed space within the temporal bone of the skull. It is found between the tympanic membrane, also known as the eardrum, and the inner ear. The auditory tube, referred to as the Eustachian or pharyngotympanic tube, is located there, lying toward the front of the overall structure of the auditory system. It connects the middle ear to the pharynx via the nasopharynx, or nasal passageways. In adults, this small tube typically averages about 1.5 inches (35 mm) in length.
The auditory tube assists with two important physiologic functions: balance and hearing. To carry out its work, this structure must be capable of opening and closing properly. Normally the auditory tube remains in a closed position, but when necessary, it opens just enough to admit the correct amount of air needed to equalize the pressure in the middle ear with the atmospheric pressure outside the ear.
This equalization process, sometimes referred to as clearing of the ears, will be most active when one is traveling in a mountainous region or flying in an aircraft. At certain elevations, one's hearing is decreased or becomes muffled until the pressure balance is restored, usually by chewing, swallowing or using the Valsalva maneuver, in which an attempt to breathe out is made while the mouth is closed and the nose is pinched shut. When the correct pressure is achieved between the air in the middle ear and the ambient air, a popping noise will occur, and the Eustachian tube will return to its closed position to maintain the appropriate pressure and to protect the eardrum from loud noises.
Another important job performed by the auditory tube is the drainage of mucosal fluids away from the tympanic cavity of the middle ear. Fluid secretions are moved toward the nasopharynx by ciliated cells along the tube's distal end. This function can be impaired if the tube is slow to drain, which can be caused by swelling of the tissues. Such swelling can be brought about by inflammation related to allergies or infections of the upper respiratory system. A swollen Eustachian tube can cause bacteria to become trapped in the middle ear, leading to an ear infection.
Children tend to have more problems with earaches and infections than adults, because their Eustachian tube is shorter and has a more horizontal angle. The horizontal positioning, combined with a smaller tube opening in children, can impair the movement of normal secretions from the middle ear. This can result in pain and infection.