What is the inner ear?
The inner ear is an organ that combines two functions: hearing and the sense of balance. The inner ear is located in the petrous pyramid (part of the temporal bone) and is adjacent to the wall of the tympanic cavity, to which it is connected via the oval and round window. This is where the actual organ of hearing and the organ of balance are located.
Organ of balance
Read everything you need to know about the sense of balance in the article Organ of balance.
Inner ear: structure
The petrous pyramid contains a complex system of cavities, the bony labyrinth (cochlea). It contains a fluid (called perilymph) that is similar in composition to cerebrospinal fluid. The bony labyrinth also contains the membranous labyrinth – delicate tubes with a wafer-thin membrane filled with endolymph. This is rich in protein and potassium and is similar in composition to cell fluid.
Cochlea
The cochlea is a duct that winds two and a half times around its bony axis (modiolus). It is divided into three tubes along its entire length: In the middle is the cochlear duct (ductus cochlearis), filled with endolymph. Below this is the tympanic staircase (scala tympani) and above this the vestibular staircase (scala vestibuli) – both filled with perilymph.
The cochlear duct and tympanic staircase are separated from each other by the basilar membrane, on which the actual organ of hearing is located – the organ of Corti, consisting of around 25,000 sensory cells or hair cells.
This is how the stimulus travels from the middle ear to the auditory nerve
The vibrations of the stirrup in the middle ear trigger vibrations in the membranes of the inner ear, which move in waves (traveling wave) across the basilar membrane towards the tip of the cochlea. For each frequency, there is a specific point in the cochlea at which the traveling wave has its highest peak.
The outer hair cells are bent most strongly in the area of the maximum traveling wave, which creates receptor potentials that amplify the traveling wave. This is followed by excitation of the inner hair cells, which in turn leads to receptor potentials that trigger the release of a transmitter at the inner hair cells, which ultimately excites the auditory nerve. It transmits the incoming information to the brain.
With sensorineural hearing loss (sensorineural hearing loss), the sound signals in the inner ear are perceived differently because frequencies are lost. Possible causes include certain medications (such as certain antibiotics), sudden hearing loss, inner ear diseases and infections that spread to the inner ear (such as mumps, measles, Lyme disease). Toxic causes are also possible.
Hearing loss is a sudden onset of inner ear hearing loss, usually caused by circulatory disorders.
Dizziness can be caused by diseases of the vestibular system in the inner ear.
Tinnitus (ringing in the ears) can occur after a sudden hearing loss or due to circulatory disorders and vasoconstriction.
Meniere’s disease is a disease of the inner ear that is accompanied by spinning dizziness, tinnitus and sensorineural hearing loss.
Tumors in the inner ear area are also possible.
