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
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
between the
posterior cranial fossa
The posterior cranial fossa is part of the cranial cavity, located between the foramen magnum and tentorium cerebelli. It contains the brainstem and cerebellum.
This is the most inferior of the fossae. It houses the cerebellum, medulla and pons. ...
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 th ...
.
Structure
The opening to the meatus is called the porus acusticus internus or internal acoustic opening. It is located inside the
posterior cranial fossa
The posterior cranial fossa is part of the cranial cavity, located between the foramen magnum and tentorium cerebelli. It contains the brainstem and cerebellum.
This is the most inferior of the fossae. It houses the cerebellum, medulla and pons. ...
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.
Function
The internal auditory meatus provides a passage through which the
vestibulocochlear nerve (CN VIII), the
facial nerve
The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of taste ...
(CN VII), and the
labyrinthine artery
The labyrinthine artery (auditory artery, internal auditory artery) is a branch of either the anterior inferior cerebellar artery or the basilar artery. It accompanies the vestibulocochlear nerve (CN VIII) through the internal acoustic meatus. ...
(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
The vestibular ganglion (also called Scarpa's ganglion) is the ganglion of the vestibular nerve. It is located inside the internal auditory meatus.
The ganglion contains the cell bodies of bipolar neurons whose peripheral processes form synaptic ...
.
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
The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the pinna to the eardrum and is about in length and in diameter.
Str ...
References
External links
*
* ()
Diagram of Porus acusticus internus
{{Authority control
Foramina of the skull