The anatomy of the ear consists of the outer, middle, and inner ear. The shape and form of the outer ear help direct sounds to the eardrum. The middle ear contains the three small bones that pass along the vibrations reaching the eardrum to the inner ear. The inner ear contains structures that allow information about the vibrations to be carried to the brain, where they are processed as sound. The inner ear also contains structures that are important for balance and orientation.
The outer ear consists of the auricle, sometimes called the pinna, and the external auditory canal. The auricle is what most people think of as the ear, the flexible structure surrounding the ear canal. Beneath the skin, the auricle's structure is made of cartilage, except at the lobule or ear lobe. It channels sound through the external auditory canal, a 1-inch (2.5-cm) tube that is made of cartilage, before it passes through the temporal bone of the skull. Vibrations passing through the external canal strike the tympanic membrane, popularly called the eardrum.
In the anatomy of the ear, the tympanic membrane separates the outer and middle parts. The middle ear is a small cavity containing air. It is separated from the inner ear by bone, which contains two openings. These openings are called the round and oval windows. The middle ear is also connected to the pharynx via the pharyngotympanic tube, sometimes called the eustachian tube. This tube allows the air pressure in the middle to be the same as that on the outside, which is sometimes felt to balance out when ears pop.
The middle ear contains the three smallest bones in the body, the malleus, incus, and stapes. These are sometimes known as the hammer, anvil, and stirrup. In the anatomy of the ear, they are sometimes known as the auditory ossicles. These three bones serve to amplify vibrations before they reach the inner ear.
The inner ear is sometimes called the labyrinth and consists of two parts. The bony labyrinth is actually a cavity in part of the temporal bone of the skull and consists of the semicircular canals, vestibule, and cochlea. The membranous labyrinth is made up of ducts that line each of these spaces. The utricle and sacule, located in the vestibule, contain receptors that give information about the orientation of the head when it is still. Structures in the semicircular canals monitor rotational movements of the head.
The cochlea is the deepest part in the anatomy of the ear. It contains the cochlear duct, which senses the vibrations reaching it through the external and middle anatomy of the ear. Within the cochlea, the spiral organ of Corti contains the inner and outer hair cells, which are actually the receptors for these vibrations. These cells pass information through the cochlear nerve to the brain, where vibrations are interpreted as distinct sounds.