The eustachian tube is a narrow channel about 1 1/2 inches (4 centimeters) long, which connects the middle |ear| with the throat. The opening is located in the pharyngeal portion of the |nose| (back of the throat). The tube travels upward and back and to the side of the |ear| and enters the floor of the middle |ear|. The eustachian tube assures that ~air~ pressure inside and outside the middle |ear| remains identical. It normally is closed, but opens whenever a person yawns or swallows to protect the delicate parts of the |ear| from abrupt changes in the ~air~ pressure. If the two ~air~ pressures are different, the |eardrum| will not respond correctly to the pressure fluctuations of sound waves.
