Ear tubes are actually called Eustachian tubes, or the auditory tubes. They are short, small cartilage and bone canals that connect the middle ear, an air-filled cavity, and the nasopharynx, which is better pictured as the lower nasal cavity behind the mouth. This allows air to enter and leave the ear, thus keeping the pressure equal to the external atmospheric pressure. If this did not occur, the eardrum would not vibrate properly.
Sound waves travel through the air and enter the ear. They proceed through the middle ear to vibrate the bones and structures of the inner ear via the eardrum. This then transmits the signals to the brain where they are integrated and we hear the sound. Without a maintained pressure within the ear, the vibrations, and therefore the sounds, are altered.
Sometimes we can feel the pressure adjust. A popping sensation or sound is often felt when altitude is changed, such as when driving up a mountain or flying in an airplane. Swallowing, chewing, or yawning can often help the Eustachian tubes open by pulling on the neck muscles, thus releasing the pressure in the ears. Anyone who has had the experience of their ears not popping knows first hand that a lack of pressure equilibrium leads to temporary hearing problems or deafness.
The Eustachian tubes also allow mucus to drain from the ears. As those who have had complicated strep throat or other upper respiratory infections already know, blockage can result in an ear ache and the infection can potentially spread to the inner ear via the Eustachian tubes. In children, who often have a more horizontal tube, the drainage is sometimes blocked anatomically and results in a greater occurrence of ear infections. Synthetic tubes are sometimes inserted by a doctor to help keep the earway open and facilitate appropriate air and fluid exchange. Since the tube opens into the pharynx, the mucus drains into the stomach similarly to the sinuses.
Although there are some ideas that the Eustachian tubes help maintain balance, this is actually accomplished by hair cells in the inner ear, called the vestibular system. However, appropriate air pressure within the ear can affect the function of the ear structures and infections are known to affect equilibrium. Another condition sometimes mistaken for occurring with the Eustachian tubes is swimmer's ear. Water or pollutants may become trapped in the ear canal, not the Eustachian tubes, and lead to an ear ache followed by inflammation and infection. A blockage in the ear canal does have similar signs as a tube blockage though, dulled hearing and pain, as it prevents air movement to the inner ear as well.