How the Ear Works
Sound entering the ear canal causes vibrations of the tympanic membrane (eardrum). The eardrum is attached to one of three ossicles (bones) found in the middle ear called the malleus. The malleus bone transmits the mechanical vibrations to another ossicle, the incus, which in turn transmits the vibrations to the smallest of the three ossicles, the stapes. The stapes bone vibrates and transmits the mechanical energy to the inner ear. The inner ear is made of a bony labyrinth filled with fluid and membranes. As the stapes vibrates, the fluid in the inner ear is set into motion. The cilia on the ends of hair cells within the inner ear are bent and an electrical signal is generated. This travels along the cochlear (hearing) nerve and then back to the brain. The inner ear is composed of the cochlea, which is responsible for hearing, and the semicircular canals that convey balance information concerning angular acceleration of the head back to the brain. Two other organs, the saccule and the utricle, found in the inner ear detect linear acceleration of the head.
The internal auditory canal contains three different types of nerves: the cochlear (hearing), vestibular (balance) and facial nerve. The facial nerve is responsible for contraction of the facial muscles, thus allowing motion of the face on that side. This is the nerve that is responsible for our ability to raise our eyebrows, close our eyes, flare our nostrils, and raise the corner of the mouth on that side. It is also responsible for conducting information regarding taste from the front 2/3 of the tongue and also tear production from the lacrimal glands.
The superior and inferior vestibular nerves (or upper and lower balance nerves) transmit linear and angular acceleration data to the central nervous system.