Ear, inner: There are three sections of the ear. They are the external ear, the middle ear, and the inner ear. The inner 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 larger of the two sacs, the utriculus, is the principal organ of the vestibular system or system of balance. This system informs us about the position and movement of the head. The smaller of the two sacs, the sacculus, is also connected by membranous tube to the cochlea that contains the organ of Corti. The hair cells, which are the special sensory receptors for hearing, are found within the organ of Corti.

The inner ear is also called the internal ear.