How the Ear Works
The ear consists of three parts: the outer ear, which consists of the pinna (visible ear), ear canal, and ends at the ear drum (tympanic membrane); the middle ear from the ear drum inwards, including the three ossicles (bones of hearing) – the malleus (hammer), incus (anvil) and stapes (stirrup) surrounded by air; and the inner ear, including the cochlea (hearing portion) and vestibule (balance portion), surrounded by the densest bone in the body, the otic capsule. The Eustachian tube connects the back portion of the nose to the middle ear, in order to equalize air pressures in the middle ear space and drain any fluid in the middle ear. An important structure that runs through the middle ear and mastoid bone is the facial nerve, which gives movement to that side of the face.
Normally, sound waves enter the ear canal and get to the ear drum. The sound energy is conserved by the coordinated movement of the ossicles and sent to the cochlea. Movement of the fluid in the cochlea stimulates several of the tens of thousands of nerve endings in the inner ear. The sound energy, which has now changed from air to fluid to electrical enery, is transmitted along the cochlear (hearing) nerve to the brain where it is heard.
The normal sense of balance is determined in the brainstem with input from both right and left inner ears (vestibular system), both right and left eyes (visual system), and right and left muscles of the back, legs and soles of the feet (proprioceptive system). Although all inputs are important, the most meaningful information regarding balance is sent by the inner ear vestibular sense organs.
In the inner ear, there are three semicircular canals on each side. These canals respond to angular acceleration. There are also two otolithic organs on each side, and they respond to gravitational changes. The vestibular (balance) portion of the inner ear is bathed in the same fluids as the cochlear (hearing) portion of the inner ear.