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