The internal auditory meatus (also meatus acusticus internus, internal acoustic meatus, internal auditory canal, or internal acoustic canal) is a canal within the
petrous part of the temporal bone of the
skull between the
posterior cranial fossa and the
inner ear
The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...
.
Structure
The opening to the meatus is called the porus acusticus internus or internal acoustic opening. It is located inside the
posterior cranial fossa of the skull, near the center of the posterior surface of the petrous part of the temporal bone. The size varies considerably. Its outer margins are smooth and rounded.
The canal which comprises the internal auditory meatus is short (about 1 cm) and runs laterally into the bone.
The lateral (outer) aspect of the canal is known as the fundus. The fundus is subdivided by two thin crests of bone to form three separate canals, through which course the
facial and
vestibulocochlear nerve branches. The falciform crest first divides the meatus into superior and inferior sections; a vertical crest (Bill's bar, named by
William F. House
William Fouts House (December 1, 1923 in Kansas City, Missouri – December 7, 2012 in Aurora, Oregon) was an American otologist, physician and medical researcher who developed and invented the cochlear implant. The cochlear implant is considered ...
) then divides the upper passage into anterior and posterior sections.
Although there are three osseous canals, the fundus is conceptually divided more commonly into four quadrant areas according to the four major nerve branches of the inner ear:
* anterior superior - facial nerve area (contains facial nerve and
nervus intermedius)
* anterior inferior - cochlear nerve area (contains cochlear nerve)
* posterior superior - superior vestibular area (contains superior division of vestibular nerve)
* posterior inferior - inferior vestibular area (contains inferior division of vestibular nerve)
The cochlear and vestibular branches of cranial nerve VIII separate according to this schema and terminate in the inner ear. The facial nerve continues traveling through the
facial canal, eventually exiting the skull at the
stylomastoid foramen
The stylomastoid foramen is a foramen between the styloid and mastoid processes of the temporal bone of the skull. It is the termination of the facial canal, and transmits the facial nerve, and stylomastoid artery. Facial nerve inflammation in th ...
.
Function
The internal auditory meatus provides a passage through which the
vestibulocochlear nerve (CN VIII), the
facial nerve (CN VII), and the
labyrinthine artery (an internal auditory branch of the
anterior inferior cerebellar artery in 85% of people) can pass from inside the skull to structures of the inner ear and face. It also contains the
vestibular ganglion.
Additional images
File:Base of skull 17.jpg, Internal acoustic meatus
File:Gray144.png, Temporal bone at birth. Inner aspect.
File:Gray193.png, Base of the skull. Upper surface.
File:Gray908.png, Horizontal section through left ear; upper half of section.
File:Gray923.png, The cochlea and vestibule, viewed from above.
File:Occipital bone dissection.jpg, Tympanic cavity. Facial canal. Internal carotid artery.
See also
*
External auditory meatus
References
External links
*
* ()
Diagram of Porus acusticus internus
{{Authority control
Foramina of the skull