The bones of the inner ear transmit sound, but they also do much more. They help maintain a sense of balance; problems with the bones in the inner ear can result in vertigo, or dizziness. The bones of the inner ear are part of the bony labyrinth, a fluid filled series of tubes. The front part of the bony labyrinth contains the cells that help you hear. The middle and back sections maintain balance. The inner ear actually lies within the skull.
Cochlea
The cochlea, a snail-shaped bone, converts impulses from the outer and middle ears into electrical impulses that travel through the auditory nerve to the brain. The cochlea is divided into three sections. The first two transmit sound by pressure changes in the fluid that fills them, called endolymph, and the third, the organ of Corti, sends impulses to the brain that are transmitted into sound when hair cells that line the area receive signals.
The cochlea's snail shape appears to help the bone transmit low frequency sounds, according to an article entitled "Cochlea's Graded Curvature Effect on Low Frequency Waves" published in the American Physical Society in March 2006 by lead author Daphne Manoussaki of the Vanderbilt Mathematics Department.
Loss of hair cells as people age is one cause of age-related hearing loss. Cochlear implants can help people who have severe hearing loss.
Vestibule
The vestibule connects the semi-circular canals with the cochlea. The vestibule's function is to detect motion and maintain balance and equilibrium. The vestibule is filled with endolymph, a fluid similar to that found in the spinal cord. Two sac-like structures, the utricle and saccule, also lie within the vestibule. Each sac contains a macula, a structure that contains sensory hair cells and stones called otoliths. Both the hair cells and the otoliths are surrounded by gelatinous material. When the head moves up and down or side to side, the otoliths move into contact with parts of the sensory hair cells, which transmit the data received to nerve cells.
Semi-circular Canals
There are three semi-circular canals; each stands at approximately right angles to the other two. This arrangement allows them to detect movement in different directions. The canals are filled with endolymph. At the start of each of the semi-circular canals is an ampulla, or swollen area, which contains the crista.
Cristae contain sensory hair cells that are activated when the endolymph moves within the canals, and are sensitive to rotational movement and the rate at which the head is moving. Cristae are similar to maculae but don't contain otoliths.
Movement of the sensory hair cells trigger nerve impulses that result in reflex actions. If the hair cells detect sideways movement suggesting a person is falling over, the impulse to put an arm out to catch himself is triggered, says Partners in Assistive Technology Training and Services.
