4.1.2 What does the Ear Drum do?
The ear drum vibrates and transmits sound vibrations through to the middle and inner ear.
Just like the skin on a drum, the eardrum vibrates when it is hit by the incoming sound waves. It then passes on the vibration of these sounds to the rest of the ear.
The ear drum is in contact both with the hammer bone and also the bony ridge of the tympanic sulcus, around its circumference. The sound vibrations pass into the hammer and then the ossicular chain of little bones in the middle ear. It is also significant, according to Dr Tomatis, that vibrations from the ear drum also pass directly into the cranial bone via the tympanic sulcus. In this way some sound can reach the inner ear directly, even if the middle ear has been damaged.
The ear drum also serves to protect the middle ear from substances, moisture and toxins which may enter through the outer ear canal.
The ear drum is innervated (supplied) by four cranial nerves: the trigeminal (5th), the facial (7th), the glassopharyngeal (9th) and the vagus (10th).
Being flexible, the ear drum allows for a certain amount of pressure imbalance between the middle ear and the outside air. However, the ear drum gives us a sensation of pain, discomfort or fullness if it is being stretched by too much or too little air pressure being held within the middle ear. Thus, it is responsible for letting us know if the Eustachian tube is blocked or not equalising normally.
If the ear drum has been perforated, it will not vibrate quite as well, so there may be some reduction to a person’s hearing. There is also the chance for debris, water or infection to enter into the middle ear. A person with a perforation should wear good ear plugs with petroleum jelly if they go swimming, and must not immerse their head under water.
Small perforations may heal by themselves or can be surgically repaired if needed. Remaining scar tissue on the ear drum may have some effect on a person’s hearing ability.