There are three sections of the ear. They are the external
ear, the middle ear, and the internal ear. The internal ear is far and away the
most highly complex. The essential component of the inner ear for hearing is the
membranous labyrinth where the fibers of the auditory nerve (the nerve connecting
the ear to the brain) end. The membranous labyrinth is a system of communicating
sacs and ducts (tubes) filled with fluid (the endolymph). The membranous labyrinth
is lodged within a cavity called the bony labyrinth. At some points the membranous
labyrinth is attached to the bony labyrinth and at other points the membranous labyrinth
is suspended in a fluid (the perilymph) within the bony labyrinth.
The bony labyrinth has three parts: a central cavity (the vestibule), semicircular
canals (which open into the vestibule) and the cochlea (a snail-shaped spiral tube).
The membranous labyrinth also has a vestibule which consists of two sacs (called
the utriculus and sacculus) connected by a narrow tube. The utriculus, the larger
of the two sacs, is the principal organ of the vestibular system (which informs
us about the position and movement of the head). The smaller of the two sacs, the
sacculus (literally, the little sac) is connected with a membranous tube in the
cochlea containing the organ of Corti. It is in the organ of Corti that are situated
the hair cells, the special sensory receptors for hearing. The internal ear is also
called the inner ear.
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