The inner ear has two functional parts: the vestibular complex which is responsible for the sense of balance and the cochlea which is responsible for hearing.
It is made up of a series of tubes in the temporal bone of the skull. The inner surface of this bony tube is called the bony labyrinth. The bony labyrinth encloses a membranous structure which is called the membranous labyrinth.
Between the inner surface of the bony labyrinth and the outer surface of the membranous labyrinth is a space, the perilymphatic space, which is occupied by a fluid called the perilymph. The inner part of the membranous labyrinth contains a different type of fluid called the endolymph.
Anatomically, the bony labyrinth can be segmented into three areas, the vestibule and the semi-circular canals, both of which make up the vestibular complex and a third segment which is a spiral-shaped chamber which houses the cochlear duct. Receptors within the cochlear duct provide the sense of hearing.
On each side of the cochlear duct is a perilymph filled canal, the tympanic and the vestibular canals through which pressure changes caused by sounds entering the ear travel down to the cochlear. These pressure changes stimulate receptor cells in the cochlear to produce electrical impulses through a process called transduction. These signals travel to the brain via the auditory nerve to be interpreted as sound.
The perilymph surrounds and cushions the membranous labyrinth in the vestibular system but it does not participate directly in the sense of balance.
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