The inner ear contains the sensory organs responsible for hearing and balance. The cochlea is a snail-shaped, bony structure that is the hearing part of the inner ear, while the vestibule or labyrinth contributes to our balance.
The cochlea is filled with two fluids (endolymph and perilymph), and inside the cochlea is the sensory receptor, the Organ of Corti, which contains hair cells, or the nerve receptors for hearing.
The middle ear bones transform sound into a force that pushes on a membrane (the oval window) in the cochlea, moving the fluid in the cochlea, stimulating the tiny hair cells. Signals from the hair cells are converted into nerve impulses sent out to the mid-brain, or the cochlear nucleus, via the cochlear portion of the auditory nerve, then the nerve impulses are carried through different brain structures to the hearing part (auditory cortex) of the brain.
The vestibular system is another important part of the inner ear and is responsible for the sensations of balance and coordinate head and eye fixation and postural adjustments. It uses the same kinds of fluids and detection cells (hair cells) as the cochlea uses, and sends information to the brain about the rotation and linear motion of the head and body. The type of motion detected by a hair cell depends on its associated mechanical structures, such as the curved tube of a semicircular canal or the calcium carbonate crystals (otolith) of the saccule and utricle.
All these structures work with the visual system, joint and muscle receptors to keep object in view and maintain balance. The brain receives, interprets, and processes the information from all these systems to create the sensation of balance.