ossicles are: malleus, incus, and stapes. The auditory tube connects the middle
The bony labyrinth is a complex cavity within the temporal bone. It has three
semi-circular canals, a vestibule (hallway), and a snail- shaped cochlear portion.
The membranous labyrinth is a hollow tubular structure suspended within the bony
The endolymph fills the space within the membranous labyrinth. The perilymph
fills the space between the membranous labyrinth and the bony labyrinth.
The cochlea is a spiral structure associated with hearing. It has 2-1/2 turns. Its
outer boundaries are formed by the snail-shaped portion of the bony labyrinth.
The central column of the cochlea is called the modiolus. Extending from this
central column is a spiral shelf of bone called the spiral lamina. Connecting this
shelf with the outer bony wall is a fibrous membrane called the basilar membrane.
This membrane forms the floor of the spiral portion of the membranous labyrinth
called the cochlear duct. This contains a structure with hairs, sensory receptors of
Within the bony cochlea, the space above the cochlear duct is known as the scala
vestibuli and the space below is known as the scala tympani. Between the middle
ear cavity and the upper space is an oval window called the fenestra vestibuli.
Between the middle ear cavity and the lower space is a round window called the
A sound stimulus is transferred from the stapes to the fluid perilymph of the scala
vestibuli. In response, the basilar membrane of the cochlea vibrates. The hair
cells of the organ of Corti are mechanically stimulated. This stimulation is
transferred to the neurons of the acoustic nerve, which passes out of the modiolus
into the internal auditory meatus of the temporal bone. From here, the nerve
The two sac-like portions of the membranous labyrinth are the sacculus and the
utriculus. They are filled with endolymph. On the wall of each sac is a collection of
special hair cells known as the macula, which serves as a receptor organ for static
and linear kinetic gravitational forces. The saccular macula and the utricular
macula are oriented at more or less 90 angles to each other. (para 11-35)
Extending from and opening into the utriculus are three hollow structures called
the semicircular ducts. The utriculus completes the circles for each duct. The
three ducts are all oriented at 90 angles to each other. Where it opens into the
utriculus, each semicircular duct ends in an enlargement called an ampulla.