This study unit will enable you to:
- Understand the spatial disposition of the bony and membranous structures of the internal ear.
- Name the structures which comprise this part of the ear.
- Explain the role each anatomical structure plays in the hearing and balance senses.
The internal ear is the innermost part of the ear, located in the petrous part of the temporal bone, between the tympanic cavity (middle ear) laterally and the internal acoustic meatus medially. It is formed by a number of bony cavities (bony labyrinth), which contain several membranous ducts and sacs (membranous labyrinth).
The cavities forming the bony labyrinth are the vestibule, cochlea, and three semicircular canals. These cavities are filled with a clear fluid, called perilymph. The membranous labyrinth lies suspended within the bony labyrinth, and is also filled with a fluid, the endolymph. It consists of three semicircular ducts (one inside each semicircular canal), the cochlear duct (inside the cochlea) and two sacs found in the vestibule, the saccule and the utricle.
The internal ear has two main functions, acting as a transducer transforming the mechanical energy of soundwaves into neuronal impulses (cochlear part of the internal ear), and also playing an important role in the maintenance of balance (vestibular part of the internal ear and semicircular canals).
To learn more details about the anatomy of the internal ear and the role it plays in our auditory and balance senses watch our video below.
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Our atlas images gallery will help you identify the structures of the internal ear.
|Cochlea||Snail-shell shaped structure containing perilymph.
Ductus cochlearis: membranous duct inside the cochlea dividing it into two spaces: scala vestibuli/scala tympani
The structures contained in the cochlea are related to the auditory sense.
|Vestibule||Enlargement of the bony labyrinth located between the cochlea and the semicircular canals.
Saccule: smaller, anterior membranous sac. Communicates anteriorly with the cochlear duct and posteriorly with the utricle
Utricle: larger, posterior membranous sac. Communicates anteriorly with the saccule and posteriorly with the semicircular ducts
Vestibular aqueduct: bony canal that connects the vestibule with the posterior cranial fossa through the temporal bone
Endolymphatic duct: membranous duct within the vestibular aqueduct. Ends in a cul-de-sac called endolymphatic sac.
The structures contained in the vestibule are related with balance while stationary.
|Semicircular canals and ducts||
Anterior semicircular canal and duct: vertically oriented. Detect rotation of the head in the sagittal plane.
Posterior semicircular canal and duct: vertically oriented. Detect rotation of the head in the coronal plane.
Lateral semicircular canal and duct: horizontally oriented. Detect rotation of the head in the transverse plane.
Cochlear nerve: branch of the vestibulocochlear nerve that carries auditory sensory information from the cochlea to the brain
Vestibular nerve: carries spatial information from the semicircular canals and vestibule to the brain
Superior part of vestibular ganglion: supplies utricle (utricular nerve), anterior part of saccule, anterior semicircular canal (anterior ampullary nerve) and lateral semicircular canal (lateral ampullary nerve)
Inferior part of vestibular ganglion: posterior semicircular canal (posterior ampullary nerve) and part of the saccule (saccular nerve)