Inner ear

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The inner ear is the inner area of ​​the ear and is filled with a fluid. Here the sound waves, which were transmitted from the outer ear via the middle ear to the oval window, are converted into nerve stimuli. In addition to the receptors for hearing, there are also those for balance in the inner ear.Find out everything you need to know about the inner ear: structure, function and important diseases!

What is the inner ear?

The inner ear is an organ that combines two functions: hearing and a sense of balance. The inner ear lies in the petrous pyramid (part of the temporal bone) and borders the wall of the tympanic cavity, with which it is connected via the oval and round window. This is where the actual hearing organ and the organ of equilibrium are located.

Balance organ

Read everything you need to know about the sense of balance in the article Balance Organ.

Inner ear: structure

In the petrous pyramid lies a complex cavity system, the bony labyrinth (cochlea). It contains a fluid (called perilymph), which is similar in composition to liquor (fluid in the brain and spinal cord). In addition, the membranous labyrinth is located in the bony labyrinth - delicate tubes with a wafer-thin membrane that are filled with endolymph. This is rich in protein and potassium and its composition is similar to that of cell fluid.

Cochlea

The bony cochlea, the actual hearing organ, is located directly behind the middle ear; it is separated from the middle ear by two membranes (oval and round window). The footplate of the smallest ossicle, the stapes, is movably anchored in the oval window. As a result, the vibrations that are passed on via the ossicular chain are transferred to the fluid in the cochlea.

The snail is a tunnel that winds two and a half times around its bony axis (modiolus). Its entire length is divided into three tubes: In the middle lies the cochlear duct (ductus cochlearis), filled with endolymph. Below is the tympani staircase (Scala tympani) and above it the vestibule staircase (Scala vestibuli) - both filled with perilymph.

The cochlea and the tympanic staircase are separated from each other by the basilar membrane on which the actual hearing organ is located - the organ of Corti, consisting of around 25,000 sensory cells or hair cells.

This is how the stimulus reaches the auditory nerve from the middle ear

The vibrations of the stapes in the middle ear trigger vibrations in the membranes of the inner ear, which move in waves (traveling wave) across the basilar membrane to the tip of the cochlea. For each frequency there is a certain point in the snail at which the traveling wave has its highest deflection.

In the area of ​​the maximum of the traveling wave, the outer hair cells are bent most strongly, whereby receptor potentials arise here, which amplify the traveling wave. This is followed by excitation of the inner hair cells, which in turn leads to receptor potentials, which trigger a transmitter release on the inner hair cells, which ultimately excites the auditory nerve. It forwards the received information to the brain.

What problems can the inner ear cause?

In the case of inner ear hearing loss (sensorineural hearing loss), the sound signals in the inner ear are perceived differently because frequencies are lost. Possible causes are, for example, certain medications (such as certain antibiotics), sudden hearing loss, inner ear diseases and infections that spread to the inner ear (such as mumps, measles, borreliosis). Toxic causes are also possible.

Sudden hearing loss is a sudden onset of hearing loss in the inner ear, usually caused by circulatory disorders.

Dizziness can result from diseases of the organ of equilibrium in the inner ear.

Tinnitus (ringing in the ears) can occur after a sudden hearing loss or with circulatory disorders and vasoconstriction.

Meniere's disease is a disease of the inner ear that is associated with vertigo, tinnitus and sensorineural hearing loss.

Tumors in the inner ear area are also possible.

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