<P> The middle ear is hollow . In a high - altitude environment or on diving into water , there will be a pressure difference between the middle ear and the outside environment . This pressure will pose a risk of bursting or otherwise damaging the tympanum if it is not relieved . If middle ear pressure remains low , the ear drum may become retracted into the middle ear < cite > . One of the functions of the Eustachian tubes that connect the middle ear to the nasopharynx is to help keep middle ear pressure the same as air pressure . The Eustachian tubes are normally pinched off at the nose end , to prevent being clogged with mucus , but they may be opened by lowering and protruding the jaw ; this is why yawning or chewing helps relieve the pressure felt in the ears when on board an aircraft . </P>
besides connecting the pharynx to the ear what other purpose does the eustachian tube serve
to help keep middle ear pressure the same as air pressure