Editing Inner ear (section)

==Structure==
[[File:Gray923.png|thumb|The [[cochlea]] and [[Vestibule of the ear|vestibule]], viewed from above.]]
The labyrinth can be divided by layer or by region.

===Bony and membranous labyrinths===
The [[bony labyrinth]], or osseous labyrinth, is the network of passages with bony walls lined with [[periosteum]]. The three major parts of the bony labyrinth are the [[vestibule of the ear]], the [[semicircular canals]], and the [[cochlea]]. The [[membranous labyrinth]] runs inside of the bony labyrinth, and creates three parallel fluid filled spaces. The two outer are filled with [[perilymph]] and the inner with endolymph.<ref>{{Cite journal |last1=Rask-Andersen |first1=Helge |last2=Liu |first2=Wei |last3=Erixon |first3=Elsa |last4=Kinnefors |first4=Anders |last5=Pfaller |first5=Kristian |last6=Schrott-Fischer |first6=Annelies |last7=Glueckert |first7=Rudolf |date=November 2012 |title=Human Cochlea: Anatomical Characteristics and their Relevance for Cochlear Implantation |journal=[[The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology]] |volume=295 |issue=11 |pages=1791–1811 |doi=10.1002/ar.22599 |pmid=23044521 |s2cid=25472441}}</ref>

===Vestibular and cochlear systems===
In the [[middle ear]], the energy of [[sound pressure|pressure waves]] is translated into mechanical vibrations by the three auditory ossicles. Pressure waves move the tympanic membrane which in turns moves the malleus, the first bone of the middle ear. The malleus articulates to incus which connects to the stapes. The footplate of the stapes connects to the oval window, the beginning of the inner ear. When the stapes presses on the oval window, it causes the perilymph, the liquid of the inner ear to move. The middle ear thus serves to convert the energy from sound pressure waves to a force upon the perilymph of the inner ear. The oval window has only approximately 1/18 the area of the tympanic membrane and thus produces a higher [[pressure]]. The cochlea propagates these mechanical signals as waves in the fluid and membranes and then converts them to nerve impulses which are transmitted to the brain.<ref>{{cite book
 | title = Auditory Neuroscience
 | author = Jan Schnupp, Israel Nelken and Andrew King
 | publisher = MIT Press
 | year = 2011
 | isbn = 978-0262113182
 | url = https://mustelid.physiol.ox.ac.uk/drupal/?q=ear
 | access-date = 2011-04-13
 | archive-url = https://web.archive.org/web/20120307161941/https://mustelid.physiol.ox.ac.uk/drupal/?q=ear
 | archive-date = 2012-03-07
 | url-status = dead
 }}</ref>

The vestibular system is the region of the inner ear where the semicircular canals converge, close to the cochlea. The vestibular system works with the visual system to keep objects in view when the head is moved. Joint and muscle receptors are also important in maintaining balance. The brain receives, interprets, and processes the information from all these systems to create the sensation of balance.

The vestibular system of the inner ear is responsible for the sensations of balance and motion.  It uses the same kinds of fluids and detection cells ([[hair cells]]) as the cochlea uses, and sends information to the brain about the attitude, rotation, and linear motion of the head.  The type of motion or attitude detected by a hair cell depends on its associated mechanical structures, such as the curved tube of a semicircular canal or the calcium carbonate crystals ([[otolith]]) of the [[saccule]] and [[utricle (ear)|utricle]].

===Development===
The human inner ear develops during week 4 of [[embryonic development]] from the [[auditory placode]], a thickening of the [[ectoderm]] which gives rise to the [[bipolar neuron]]s of the [[Scarpa's ganglion|cochlear]] and [[Spiral ganglion|vestibular ganglions]].<ref>{{cite book|last=Hyman|first=Libbie Henrietta |title=Hyman's comparative vertebrate anatomy |url=https://books.google.com/books?id=VKlWjdOkiMwC|access-date=2011-05-14|edition=3|year=1992|publisher=[[University of Chicago]] Press|isbn=0226870138|page=634}}</ref> As the auditory placode invaginates towards the embryonic [[mesoderm]], it forms the auditory vesicle or ''otocyst''.

The [[auditory vesicle]] will give rise to the utricular and saccular components of the [[membranous labyrinth]]. They contain the sensory hair cells and [[otolith]]s of the [[macula of utricle]] and [[macula of saccule|of the saccule]], respectively, which respond to [[linear acceleration]] and the force of [[gravity]]. The utricular division of the auditory vesicle also responds to [[angular acceleration]], as well as the [[endolymphatic sac]] and [[Endolymphatic duct|duct]] that connect the saccule and utricle.

Beginning in the fifth week of development, the auditory vesicle also gives rise to the [[cochlear duct]], which contains the spiral [[organ of Corti]] and the [[endolymph]] that accumulates in the membranous labyrinth.<ref name=USMLE>{{cite book|last=Brauer|first=Philip R. |title=Human embryology: the ultimate USMLE step 1 review |url=https://books.google.com/books?id=_Cb_XXR5HCQC|access-date=2011-05-14|year=2003|publisher=[[Elsevier]] Health Sciences|isbn=156053561X|page=61}}</ref> The [[Reissner's membrane|vestibular wall]] will separate the cochlear duct from the perilymphatic [[scala vestibuli]], a cavity inside the cochlea. The [[basilar membrane]] separates the cochlear duct from the [[scala tympani]], a cavity within the cochlear labyrinth. The lateral wall of the cochlear duct is formed by the [[spiral ligament]] and the [[stria vascularis]], which produces the [[endolymph]]. The [[hair cells]] develop from the lateral and medial ridges of the cochlear duct, which together with the [[tectorial membrane]] make up the organ of Corti.<ref name=USMLE />

===Microanatomy===
[[File:Cochlea-crosssection.svg|thumb|A cross-section of the [[cochlea]] showing the [[organ of Corti]].]]
[[File:Organ of corti.svg|thumb|Cross-section through the spiral organ of Corti at greater magnification.]]

Rosenthal's canal or the spiral canal of the cochlea is a section of the bony labyrinth of the inner ear that is approximately 30&nbsp;mm long and makes 2¾ turns about the [[modiolus (cochlea)|modiolus]], the central axis of the cochlea that contains the [[spiral ganglion]].

Specialized inner ear cell include: hair cells, pillar cells, Boettcher's cells, Claudius' cells, spiral ganglion neurons, and Deiters' cells (phalangeal cells).

The hair cells are the primary auditory receptor cells and they are also known as auditory sensory cells, acoustic hair cells, auditory cells or cells of Corti. The [[organ of Corti]] is lined with a single row of inner hair cells and three rows of outer hair cells. The hair cells have a hair bundle at the apical surface of the cell. The hair bundle consists of an array of actin-based stereocilia. Each stereocilium inserts as a rootlet into a dense filamentous actin mesh known as the cuticular plate. Disruption of these bundles results in hearing impairments and balance defects.

Inner and outer pillar cells in the organ of Corti support hair cells. Outer pillar cells are unique because they are free standing cells which only contact adjacent cells at the bases and apices. Both types of pillar cell have thousands of cross linked [[microtubule]]s and [[actin]] filaments in parallel orientation. They provide mechanical coupling between the [[basement membrane]] and the [[mechanoreceptor]]s on the hair cells.

[[Boettcher cell|Boettcher's cells]] are found in the organ of Corti where they are present only in the lower turn of the cochlea. They lie on the basilar membrane beneath Claudius' cells and are organized in rows, the number of which varies between species. The cells interdigitate with each other, and project [[microvillus|microvilli]] into the intercellular space. They are supporting cells for the auditory hair cells in the organ of Corti. They are named after German pathologist [[Arthur Böttcher]] (1831–1889).

[[Claudius cell|Claudius' cells]] are found in the organ of Corti located above rows of Boettcher's cells. Like Boettcher's cells, they are considered supporting cells for the auditory hair cells in the organ of Corti. They contain a variety of [[aquaporin]] water channels and appear to be involved in ion transport. They also play a role in sealing off endolymphatic spaces. They are named after the German anatomist [[Friedrich Matthias Claudius]] (1822–1869).

[[Deiters cell|Deiters' cells]] (phalangeal cells) are a type of [[neuroglia]]l cell found in the organ of Corti and organised in one row of inner phalangeal cells and three rows of outer phalangeal cells. They are the supporting cells of the hair cell area within the cochlea. They are named after the German pathologist Otto Deiters (1834–1863) who described them.

[[Hensen cell|Hensen's cells]] are high columnar cells that are directly adjacent to the third row of Deiters' cells.

[[Hensen's stripe]] is the section of the tectorial membrane above the inner hair cell.

[[Nuel's spaces]] refer to the fluid-filled spaces between the outer pillar cells and adjacent hair cells and also the spaces between the outer hair cells.

[[Hardesty's membrane]] is the layer of the tectoria closest to the reticular lamina and overlying the outer hair cell region.

[[Reissner's membrane]] is composed of two cell layers and separates the scala media from the scala vestibuli.

[[Huschke's teeth]] are the tooth-shaped ridges on the spiral limbus that are in contact with the tectoria and separated by interdental cells.

=== Blood supply ===
The bony labyrinth receives its blood supply from three arteries:
1 – Anterior tympanic branch (from maxillary artery).
2 – Petrosal branch (from middle meningeal artery).
3 – Stylomastoid branch (from posterior auricular artery).
The [[membranous labyrinth]] is supplied by the [[labyrinthine artery]].
Venous drainage of the inner ear is through the labyrinthine vein, which empties into the [[sigmoid sinus]] or [[inferior petrosal sinus]].