Definition
The eardrum, also called tympanic membrane (Membrana tympani), is an essential part of the sound conducting apparatus of the human ear and forms the boundary between the external auditory canal and the middle ear.
Anatomy
The round to longitudinal oval eardrum measures about 9-11mm in its longest diameter and is only 0.1mm thick. Its largest part, the pars tensa, is stretched by a fibrous cartilage ring, which in turn is fused with the bone of the auditory canal. However, the eardrum does not form a taut and straight membrane, but a kind of funnel, the lowest point of which is fused with the tip of the hammer handle.
This is even visible from the outside through the thin eardrum. When sound waves hit this funnel, it is set in vibration and transmits the sound via the ossicles (hammer, anvil and stapes) to the inner ear. This process leads to an amplification of the sound many times over.
When viewed through an otoscope, the eardrum becomes visible as a shiny surface and exhibits a characteristic light reflex. Its color is often described as gray or pearly. The eardrum is a very sensitive organ. Touches are often felt as painful and can even be accompanied by nausea and fainting. Responsible for this are various branches of the trigeminal nerve and the vagus nerve, which sensitively innervate the eardrum.
Function of the eardrum
The eardrum is a thin membrane made up of three layers, which is clamped in the ear canal. It separates the outer ear canal from the middle ear. It thus protects the sensitive middle and inner ear from dirt and prevents microorganisms such as bacteria and viruses from entering.
However, its far more important function is the transmission of sound waves. When sound waves hit our ear, they are captured by the auricle and transmitted to the eardrum via the funnel-shaped outer ear canal. The eardrum is about the size of a one cent coin in adults.
The sound waves then cause the eardrum to vibrate, which in turn is transmitted to the ossicles in the middle ear. The eardrum is directly connected to the first bone of the ossicular chain, the hammer. On the other side, the ossicles are connected to the so-called oval window.
This is also a membrane, but many times smaller than the eardrum. The difference in size between the eardrum and the oval window increases the sound pressure. In addition, a further obstacle in the path of the sound is overcome.
Up to the eardrum the sound moves in the air. The inner ear, on the other hand, which actively processes the sound and transmits the information to the brain, contains a fluid. This transition between air and liquid is bridged by the eardrum and the ossicles.
Without the ossicles, the eardrum cannot perform its function as a sound transmitter and amplifier and vice versa. During an otoscopy, i.e. an examination of the ear with a special light mirror, the eardrum can be viewed from the outside and thus certain conclusions can be drawn about its functionality. Normally, a small light reflex, caused by the light on the otoscope, appears on the eardrum. If this is missing, it means either that the eardrum has been injured or has otherwise lost its elasticity, for example due to an infection. Both are usually manifested in the form of hearing loss.