anatomy of inner ear
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Anatomy of Inner ear Anatomy of Inner ear
Dr Ramesh Parajuli,MSChitwan Medical College Teaching Hospital,Bharatpur-10,Chitwan,Nepal
The inner(internal) ear is called as labyrinth, from the complexity of its shape.
It consists of two parts:1. The bony labyrinth: A series
of cavities within the petrous part of the temporal bone.
2. The membranous labyrinth: A series of communicating membranous sacs and ducts, contained within the bony cavities.
Inner ear fluids
Membranous labyrinth= endolymphSpace between membranous and bony
labyrinth= perilymphPerilymph: Exact origin not known Serum infiltrate, CSF Rich in Na (similar to ECF and plasma)Endolymph: Origin: Stria vascularis Rich in K ion (similar to Intracellular fluid)Absorption: Endolymphatic sac
Bony(osseous) labyrinth
The bony labyrinth consists of 3 parts: 1. Cochlea: anteriorly2. Vestibule: middle3. Semicircular canals: posteriorly
Derived from Ottic capsule
The Vestibule It is central part of the bony labyrinth, and is
situated medial to the tympanic cavity, behind the cochlea, and in front of the semicircular canals.
In its lateral or tympanic wall is the fenestra vestibuli, closed by the base of the stapes and annular ligament.
Two recesses:1. Spherical recess: lodges Saccule2. Elliptical recess: lodges Utricle
Below elliptical recess is the opening of aqueduct of vestibule through which passes the endolymphatic duct
Vestibule has 5 openings of 3 Semicircular canals(SCC)
Semicircular canals(SCC)3 in numbers: Lateral(horizontal) Posterior SuperiorLies at right angles to each otherEach canal has an ampullated end and non-
ampullated endNon-ampullated ends of PSCC and SSCC unite
to form a common channel Crus commune
3 SCC have 5 openings into Vestibule
Cochlea
A spiral shaped fluid filled structure
Coiled tube making 2.5 to 2.75 turns around a central pyramid of bone= Modiolus
Thin plate of bone winding spirally around modiolus like a thread of screw= bony spiral lamina
Organ of corti through which electircal impulse(sound) are sent along the auditory(cochlear) nerve to the brain
Basal turn of cochleabony bulge in the medial wall of middle ear= Promontory
Bony Cochlea contains 3 compartments:1. Scala vestibuli: closed by stapes footplate,
contains perilymph2. Scala tympani: closed by secondary
membrane, contains perilymph.3. Scala media (membranous
cochlea):endolymph
Scala tympani is connected to subarachnoid space through aqueduct of cochlea
Scala vestibule and scala tympani connects to each other at the apex of cochlea Helicotrema
Membranous labyrinthSeries of communicating sacs and ductsFilled with endolymphWithin walls epithelium,specialized to form
sensory receptors of cochlear and vestibular labyrinth
It consists of 1. Cochlear duct2. Utricle and saccule3. Semicircular ducts4. Endolymphatic duct and sac
Cochlear duct(membranous cochlea)
Blind coiled tubeTriangular on cross section3 walls:-1. Basilar membrane: supports organ of corti2.Reissner’s membrane(Roof of cochlear duct)
separates it from scala vestibuli3. Stria vascularis: contains vascular epithelium. secrets endolymph
Cochlear duct is connected to the saccule by ductus reuniens.
Organ of Corti:contains auditory
sensory cells and complex arrangement of supporting cells
Hair cells – inner and outer
Stereocilia or “hairs”electircal
impulse(sound) are sent along the auditory(cochlear) nerve to the brain
Cochlear Hair CellsCochlear Hair Cells
Flask-shapedCylindrical shaped
Utricle and saccule Utricle and saccule
Macula(Sensory epithelium): concerned with balance i.e. linear acceleration and position of head in response to gravity
SemicircularSemicircular ducts
3 in numbersAmpulated and non-ampulated endAmpulated end of each duct contains
neuroepithelium: crista ampularis concerned with balance i.e. Angular acceleration
Endolymphatic duct and Endolymphatic duct and sacsac
Formed by the union of 2 ducts, one each from the saccule and utricule
Endolymphatic duct passes through the vestibular aqueductterminal part dilated to form endolymphatic sac
Endolymphatic sac lies between the two layers of Dura
Peripheral receptors of auditory and vestibular system
Peripheral receptors of auditory pathway: Organ of Corti: cochlear hair cells
Peripheral receptors of vestibular pathway:1.Cristae: located in ampullated ends of 3
Semicircular ducts-responds to angular acceleration2.Maculae: Located in otolith organs(i.e. utricle and
saccule)-sense position of head in response to gravity
and linear acceleration
Peripheral receptors of auditory and vestibular system
Vestibular Hair CellsVestibular Hair CellsType I vestibular cells: compare with inner cochlear hair cells (in Organ of corti)-flask(cup)shapedType II vestibular cells: compare with outer cochlear hair cells-cylindrical
Structure of crista
Structure of macula
Thank you
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