The inner ear has two peripheral sensory organs: (1) The cochlea, that is doing the transduction of hearing. (2) The labyrinth or a vestibular apparatus, that is doing the transduction of equilibrium, and relate it to the effects of both gravity and motion.
The balance sensor of the inner ear is made of three semi-circular canals and the vestibule. The inner ear is surrounded and defended by the hardest bone of the body. Inside this bone, there are liquid-filled grooves. Within the cochlea are 3 liquid filled spaces: (1) The tympanic canal. (2) The vestibular canal. (3) The middle canal.
The origin of the eighth cranial nerve is in the inner ear and it enters the brain stem. Collision of sound waves with the tympanic membrane happenes all the time. The result is vibratory movement of the membrane and the transfer of the movement to the footplate of the stapes via the osciles.
The sound energy presses the footplate into one of the liquid-filled canals of the cochlea. The liquid inside this duct vibrates and push the fluid towards the receptor cells of the organ of Corti.
This organ is the biological transducer of hearing. It makes the transduction of the mechanical energy to electrochemical current in the eighth nerve. The electric current stimulate the spiral ganglion, which sends information through the auditory component of the eighth cranial nerve to the central nervous system.
Experimental works with high energy of noise exposure in miserable animals showed that the hair cells in the organ of Corti were damaged. The theory of the broken hair cells was the dominant theory that explained the mechanism of damage in tinnitus sufferers for many years, and a basis for focusing research on the function of the inner ear.
Medical conditions that were considered an inner ear disease with relevance to tinnitus are: (1) Meniere disease. (2) Otosclerosis. (3) Atrophy of organ of Corti. (4) Cochlear vasculitis.
The structural finding of endolymphatic hydrops in the inner ear is considered part of Meniere Disease. A common symptom is vertigo.
Hair cells are also the receptor cells involved in balance. The hair cells that are found in the hearing and balance systems of the ear are not the same. Vestibular hair cells receive their mechanical signal from the flow of liquid in the semicircular canals and the utricle and saccule.
Electrochemical current (firing) of vestibular hair cells transmits the electric signal to the Vestibular component of the eighth cranial nerve.