What is the inner ear

The inner ear

The inner ear sits in the human ear and is the innermost part of the ear. It consists of the cochlea, the balance mechanism and the auditory nerve. This complex cavity system, also known as the cochlea, contains a liquid (perilymph). In addition, there is a membranous labyrinth in the cochlea, which consists of delicate tubes and a wafer-thin membrane.

Cochlea

The cochlea is located directly behind the middle ear and is connected to the tympanic cavity in the middle ear by an oval and a round window. The stirrup is movably anchored in the oval window. Here the vibrations, which are transmitted via the ossicular chain, are transferred to the fluid in the cochlea. The cochlea is a duct that winds two and a half times around its bony axis (modiolus). It is responsible for the hearing sensation and is divided into three different courses:

  • Upper vestibule stairs (scala vestibuli)
  • Cochlear duct (ductus cochlearis) in the middle
  • Timpani staircase (Scala tympani) below

The cochlea and the tympanic staircase are separated from each other by the basilar membrane on which the actual conversion of the sound stimuli takes place. This is where the organ of Corti is located, which consists of around 25,000 hair cells. The tips of the hair cells (stereovilli) reach into the tectorial membrane. If the basilar membrane is deflected by vibrations, the tips of the hair cells snap off and an electrical stimulus is generated.

auditory nerve

A tone hits the ear in the form of a sound wave and passes it on to the eardrum, which is then set in motion. These vibrations are then conducted via the ossicles to the oval window and thus to the auditory nerve. These vibrations trigger traveling waves, which move over the membranes of the inner ear over the basilar membrane to the tip of the cochlea. At every frequency there is a certain point in the cochlea at which the traveling wave has its highest peak. Then the outer hair cells are bent most strongly, whereby the traveling wave is amplified and the inner hair cells are excited. This excitation ultimately reaches the auditory nerve, which forwards the information to the brain.

Equilibrium mechanism

The sense of balance is mediated by the vestibular apparatus. This consists of two filled vesicles, sacculus and utriculus, which lie behind the oval window, as well as three semicircular canals. The two vesicles, the saccule and the utricle, measure the body's acceleration. The three semicircular canals lie or stand perpendicular to one another in space. They are divided into anterior, posterior and horizontal semicircular canals. They consist of a ring-shaped tube and an extension that carries sensory cells. Their tips protrude into a gelatinous dome, the cupula. Through the excitation in the different semicircular canals, the brain can calculate the position of the body in space, depending on the direction in which the head turns, the stimulus arises in a different arc.