Labyrinths containLabyrinths contain

Three partsThree parts

Semicircular canals Semicircular canals

Vestibular Vestibular

systemsystem

VestibuleVestibule

CochleaCochlea Auditory Auditory systemsystem

Vestibular systemVestibular system

Function: Balance and equilibriumFunction: Balance and equilibrium

Sensory cells: Hair cellsSensory cells: Hair cells

Auditory system: CochleaAuditory system: Cochlea

Name derived from snail-Name derived from snail-like shapelike shape

Tube of decreasing Tube of decreasing diameter coiled around diameter coiled around itselfitself

Coiled around a central Coiled around a central bony canal called modiolus bony canal called modiolus

Broad base, narrow apexBroad base, narrow apex

Length: About 35 mm Length: About 35 mm

In human beings: 2 and 5/8 In human beings: 2 and 5/8 coilscoils

Isolated cochlear turns from the inner ear of fetal sheep: Photo courtesy of Gerhardt, Isolated cochlear turns from the inner ear of fetal sheep: Photo courtesy of Gerhardt, K. K.

Cochlear macrostructureCochlear macrostructure

Partially divided Partially divided throughout its throughout its length by a thin length by a thin spiral shelf of bone spiral shelf of bone called called osseous osseous spiral laminaspiral lamina

At the outer At the outer (lateral) wall of the (lateral) wall of the cochlea: cochlea: Spiral Spiral ligamentligament

Between the osseous spiral Between the osseous spiral lamina and the spiral lamina and the spiral ligament: ligament: Basilar Basilar membranemembrane

Runs all the way along the Runs all the way along the length of the cochlea, length of the cochlea, except for a small opening except for a small opening at the apex called the at the apex called the helicotremahelicotrema

Reissner’s membraneReissner’s membrane projects diagonally from projects diagonally from spiral lamina to outer bony spiral lamina to outer bony wall of cochleawall of cochlea

Joins the basilar membrane Joins the basilar membrane at the helicotremaat the helicotrema

Between the osseous spiral Between the osseous spiral lamina and the spiral lamina and the spiral ligament: ligament: Basilar Basilar membranemembrane

Runs all the way along the Runs all the way along the length of the cochlea, length of the cochlea, except for a small opening except for a small opening at the apex called the at the apex called the helicotremahelicotrema

Reissner’s membraneReissner’s membrane projects diagonally from projects diagonally from spiral lamina to outer bony spiral lamina to outer bony wall of cochleawall of cochlea

Joins the basilar membrane Joins the basilar membrane at the helicotremaat the helicotrema

http://www.iurc.montp.inserm.fr/cric/audition/english/ear/fear.htm

http://epl.meei.harvard.edu/~hwang/3Dviewer/3Dviewer.html

Cross-section of the cochleaCross-section of the cochlea

Basilar membrane and Basilar membrane and Reissner’s membrane Reissner’s membrane divide the cochlear divide the cochlear canal into three ducts:canal into three ducts:

Scala vestibuliScala vestibuli Scala tympaniScala tympani Scala mediaScala media

Scala Vestibuli Scala Vestibuli

Above Reissner’s Above Reissner’s membranemembrane

Extends from oval Extends from oval window in the window in the vestibule to the vestibule to the helicotremahelicotrema

Contains perilymphContains perilymph

Scala TympaniScala Tympani

Below the basilar Below the basilar membranemembrane

Extends from round Extends from round window to the window to the helicotremahelicotrema

Contains perilymphContains perilymph

Scala media/cochlear sacScala media/cochlear sac

Bound below by Bound below by basilar membranebasilar membrane

Bound above by Bound above by Reissner’s membraneReissner’s membrane

Bound on the outer Bound on the outer side by side by Stria Stria vascularisvascularis

Contains endolymphContains endolymph

Dimensions of the cochlear partitionsDimensions of the cochlear partitions

Cochlea: Narrower toward the apexCochlea: Narrower toward the apex

Basilar membrane: Narrower at the base and wider Basilar membrane: Narrower at the base and wider toward the apical endtoward the apical end

Apical end: Flaccid and under no tensionApical end: Flaccid and under no tension

Base end: Stiff and under a small amount of tensionBase end: Stiff and under a small amount of tension

Cochlear microstructure Cochlear microstructure

Organ of CortiOrgan of Corti

Lies on the basilar Lies on the basilar membrane in the membrane in the scala mediascala media

Contains many Contains many different types of different types of specialized cellsspecialized cells

Organ of CortiOrgan of Corti

Pillar cells or rods of CortiPillar cells or rods of Corti

Provide structure and Provide structure and supportsupport

Inner and outer Inner and outer pillar cellspillar cells

Form a tunnel called Form a tunnel called tunnel of Cortitunnel of Corti

Contains fluid called Contains fluid called cortilymphcortilymph

Hair cellsHair cells

On the outer side of On the outer side of the outer pillar/rod the outer pillar/rod cells: cells: Outer hair Outer hair cells (OHC)cells (OHC)

(Away from modiolus)(Away from modiolus)

On the inner side of On the inner side of the inner pillar/rod the inner pillar/rod cells: cells: Inner hair cells Inner hair cells (IHC)(IHC)

(Toward the modiolus)(Toward the modiolus)

Supporting cellsSupporting cells

OHC supported by OHC supported by cells of cells of Deiter and Deiter and HensenHensen

IHC supported by IHC supported by border cells of border cells of the inner sulcusthe inner sulcus

Reticular laminaReticular lamina

Formed partly by the Formed partly by the phalangeal phalangeal processes of the Deiter’s cells.processes of the Deiter’s cells.

OHCOHC Around 12000 in numberAround 12000 in number

Test-tube shapedTest-tube shaped

Three-five rowsThree-five rows

IHCIHC

Around 3400 in Around 3400 in numbernumber

Flask shapedFlask shaped

Single rowSingle row

Stereocilia Stereocilia

Hairlike projectionsHairlike projections

Project from the top of Project from the top of IHC and OHCIHC and OHC

Graded in lengthGraded in length

Have cross-bridges Have cross-bridges called tip-linkscalled tip-links

Stereocilia of OHC and IHCStereocilia of OHC and IHC

OHC: OHC: 6-7 rows per OHC6-7 rows per OHC Each row has a W Each row has a W

shaped arrangementshaped arrangement

IHC: IHC: 2-4 rows per IHC2-4 rows per IHC Each row in a shallow Each row in a shallow

U-shaped U-shaped arrangementarrangement

Tectorial membraneTectorial membrane

Gelatinous transparent Gelatinous transparent membrane projecting from membrane projecting from spiral laminaspiral lamina

Attaches loosely on outer Attaches loosely on outer edge to the Deiter’s and edge to the Deiter’s and Hensen’s cells.Hensen’s cells.

Longest stereocilia of OHC Longest stereocilia of OHC embedded in inferior embedded in inferior surface of tectorial surface of tectorial membranemembrane

Stereocilia of IHC not Stereocilia of IHC not embedded in tectorial embedded in tectorial membranemembrane