eardrum

This article describes the eardrum of the ear, for the covering of the drum see vibrating membrane ; on the eardrum of insects see the tympanic organ .

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a = eardrum (red); b = hammer; c = anvil; d = stirrup; e = middle ear

Normal human left eardrum. The back of the head is on the right, the face on the left of the picture. At 11 o'clock the malleus appears , at 8 o'clock the characteristic light reflex.

The eardrum ( Membrana tympani, Myrinx ) is a thin membrane at the inner end of the ear canal (if there is one) and closes it off from the middle ear . All terrestrial vertebrates have an eardrum with the exception of the amphibians , tail amphibians , double snakes and snakes . In humans it is about 0.1 mm thick and has an area of ​​about 85 mm², of which about 55 mm² can effectively absorb sound . The longest (vertical) diameter is 9 to 10 mm.

anatomy

The main part of the eardrum ( pars tensa , "tensioned part") consists of three layers: the outer epithelial layer ( stratum cutaneum ), a stable middle fiber layer ( lamina propria ) and an inner mucous membrane ( stratum mucosum ). The hammer handle, part of the first ossicle , the hammer ( malleus ), which is fused with the eardrum , can be seen through the pars tensa . The pars tensa of the eardrum is crimped with a fibrous ring ( annulus fibrocartilagineus ) in a groove in the surrounding bone ( sulcus tympanicus ) of the auditory canal. The eardrum is not a stretched, straight membrane, but drawn inwards in a funnel shape with the lowest point ( umbo , navel) at the tip of the hammer handle in the middle of the eardrum.

Towards the external auditory canal , the pars tensa consists of a multilayered, smooth squamous epithelium that normally reflects incident light. Towards the tympanic cavity , epitympanone , there is a single-layer squamous epithelium. Both sit on a basement membrane . This is followed by the connective tissue fiber layer, lamina propria, located between the two epithelia . This shows a composite structure: on the outside the connective tissue fibers run radially ( stratum radiatum ) and inside they run circularly ( stratum circular ). Both fiber systems unite at the edge of the eardrum to form the anulus fibrocartilagineus, which enables the connection to the bone, a sulcus tympanicus .

Above, the bony border of the eardrum shows a notch, the tympanic notch . This notch is closed by the small pars flaccida ("flaccid part") of the eardrum, also called Shrapnell's membrane. The pars flaccida has no lamina propria , the ectodermal stratum cutaneum is only separated from the endodermal stratum mucosum by a basement membrane . The absence of a mesodermal interlayer is unique in the body.

The eardrum has a shiny surface and a characteristic light reflection. The color of the eardrum is described as "dove gray" or "mother-of-pearl".

The eardrum is set in vibrations by sound waves , more precisely by the alternating sound pressure  p , which are passed on from the ossicles in the middle ear to the inner ear .

Branches of several nerves are involved in the sensitive nerve supply to the eardrum, in particular the auricular branch of the vagus nerve and the auriculotemporal nerve, a branch of the trigeminal nerve .

The inside of the eardrum is supplied by branches of the nerve plexus of the middle ear mucosa ( plexus tympanicus ). Touching the eardrum is painful and in individual cases can cause discomfort, nausea and even fainting.

The eardrum is supplied with blood via an external and internal network. The outer surface of the tympanic membrane is mainly supplied by radial branches of the deep auricular artery , a branch of the maxillary artery, with a comparatively larger branch, the external manubrial artery , in the stria malleolaris running along the hammer handle from above to the middle of the eardrum. The inner network is supplied by branches of the anterior tympanic artery .

The headphone stereophony takes into account the distance between the two eardrums, which is also called the ear distance .

embryology

The layer of tissue that lines the inside of the eardrum , i.e. the middle ear , is of endodermal origin. The tissue layer that covers the connective tissue layer with its circular and radial fibers from its outside, i.e. the external auditory canal , is of ectodermal origin. The eardrum is formed from the endoderm of the first pharyngeal arch and the ectoderm of the first gill groove . The first pharynx represents a lateral protuberance of the so-called primitive pharynx. This pharyngeal protuberance is located between the first and second gill arch. The exact term is pharyngotympanic recess . It forms the tympanic cavity, Cavum tympani . Starting from here, the pharynx forms a series of small cavities in the bone of the mastoid process of the temporal bone, processus mastoideus ossis temporalis , the common entrance is also called antrum mastoideum . Adjacent to the outer part, the first pharynx is adjacent to the ectoderm of the first gill furrow, which is turned in from the outside. The first gill groove later forms the external auditory canal, meatus acousticus externus . This is where the eardrum, the membrana tympani, develops .

Diseases

Hard objects can easily cause direct injuries ( perforation ), indirect tears of the eardrum ( rupture ) from a blow to the ear or an explosion . A middle ear infection , a barotrauma , a skull fracture can cause an injury. If the eardrum is perforated, hearing is impaired depending on the position of the perforation and pathogens can enter the middle ear through the perforation (especially with water). Traumatic perforations of the eardrum show a good tendency towards spontaneous healing. If this does not occur, the eardrum defect can be surgically closed with a tympanoplasty .

Inflammation of the eardrum is known as myringitis .

Medical diagnostics

An ear speculum , otoscope or ear microscope is used to diagnose diseases of the ear . It enables the doctor to identify changes in the eardrum that are associated with diseases of the outer or middle ear .

Scheme of an otoscopic finding. Right eardrum seen from the lateral side . 1. Anvil body and hammer head (not visible), 2. Pars flaccida of the eardrum, 3. Processus brevis of the hammer, 4. Pars tensa of the eardrum, 5. Light reflex, 6.  Manubrium of the hammer (malleus) , 7. Edge of the eardrum, annulus fibrocartilagineus , 8. Incisura tympanica (Rivini)

With the tympanometry the acoustic resistance (is acoustic impedance ) of the eardrum is measured. A tympanogram is the result of this measurement. For this purpose, a sealed probe is inserted into the ear canal and the resulting change in the acoustic resistance of the eardrum is measured and recorded while the air pressure in the ear canal changes. The tympanogram enables conclusions to be drawn about the pressure in the middle ear or the content of the middle ear and the ability of the eardrum-ossicular system to vibrate.

Furthermore, the body temperature can be measured on the eardrum . One speaks of the measurement of the tympanic temperature .

Web links

Wiktionary: eardrum  - explanations of meanings, word origins, synonyms, translations

Individual evidence

1. ^ Rudolf Probst; Gerhard Grvers; Heinrich Ivo: ear, nose and throat medicine . Georg Thieme, Stuttgart 2000, ISBN 3-13-119031-0 , p. 228.
2. ↑ Jan Langmann: Medical Embryology. Normal human development and its malformations. Thieme, Stuttgart / New York 1980, ISBN 3-13-446606-6 , p. 376.

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