The Middle Ear
The eardrum separates the outer ear from the middle ear. A narrow passageway called the eustachian tube connects the middle ear to the throat and the back of the nose . The eustachian tube helps keep the eardrum intact by equalizing the pressure between the middle and outer ear. For example, if a person travels from sea level to a mountaintop, where air pressure is lower, the eardrums may cause pain because the air pressure in the middle ear becomes greater than the air pressure in the outer ear. When the person yawns or swallows, the eustachian tube opens, and some of the air in the middle ear passes into the throat, adjusting the pressure in the middle ear to match the pressure in the outer ear. This equalizing of pressure on both sides of the eardrum prevents it from rupturing. The middle ear is a narrow, air-filled chamber that extends vertically for about 15 mm (about 0.6 in) and for nearly the same distance horizontally. Inside this chamber is a linked chain of three ossicles, o