Anatomy Of Inner EAR

Presenter-Dr.Razal M Sherif Moderator-Dr.Joythi Swarup.R

Questions in previous Presentation

Malleus o Weight-23mgo Length-9mm

Incus o Weight-25-30 mg o Length of long process -7 mmo Length along short process-5mm

Stapes o Weight-2.86 mgo Height-3.26 mm

Inner Ear/Labyrinth • Development of Inner ear starts by 3rd week of IUL and completes

by 16th week.

• Cochlea sufficiently developed by 20th week (fetus can hear in the womb)

• Lies in the petrous part of the temporal bone.

• Is an important organ of hearing and balance.

• 2 Parts• Bony Labyrinth• Membranous Labyrinth

Bony Labyrinth• Vestibule• Cochlea• Semicircular Canals

Vestibule• Small Ovoid bony chamber measuring 4mm• situated between

o Laterally - Medial wall of the middle ear • is the opening of the oval window which is closed by the

footplate of the stapes o medially - by Internal auditory meatus .

• Medially(inner Surface)-2 recesseso Spherical recesses-lodges the saculeo Elliptical recesses-lodges the utricle

• Below elliptical recesses-opening of endolymphatic duct

• Postero superioro 5 openings of SCC

Semi Circular Canals• 3 semi circular canals

o Superior o Posterioro Lateral

• They lie in planes at right angle to each other.• Each canal got ampullary end ,which open in the

vestibule.• Non-ampullary end of Lateral SCC open independently • Post. SCC and Sup. SCC form a common opening

Called CRUS COMMUNE

Cochlea• Coiled tube – 35mm.• Two and half turns around a central bone called

Modiolus

MODIOLUS • Pyramidal Shaped • Base directed towards Internal Acoustic Meatus

• Vessels and Nerves enter cochlea via modiolus• Around modiolus -thin plate of bone winding

spirally is a called – Osseous Spiral lamina

• The Osseous Spiral lamina divides the bony cochlea (incompletely) into o Scala Vestibuli o Scala Tympani.

• And gives attachment to a membrane called Basilar membrane.

• Above the Osseous Spiral lamina and the Basilar membrane lies the Scala Media which contains the endolymph and Organ of Cori.

• The scala vestibuli and scala tympani are filled with perilymph and communicate with each other at the apex of cochlea through an opening called HELICOTREMA

• Scala vestibulio closed by the foot plate of stapes

• scala tympani o Closed round window membrane (secondary tympanic

membrane)• Connected to Sub arachnoid space by aqueduct

of choclea

Membranous Labyrinth

• It lies within the bony labyrinth

• Filled with Endolymph.• Space between membranous

labyrinth and bony labyrinth-Perilymph.

• It containso Cochlear Ducto Utricle and Saccule(otolith organs)o Semi circular Ducto Endolymphatic Duct and Sac

Cochlear duct• It is a blind coiled tube.

o called as Scala Media/membranous cochlea

• It appears triangular on cross-section- o One wall of triangle is the basilar membraneo Another wall of triangle is the Reissner's membraneo And the third wall is the stria vascularis,

• Cochlear duct is connected to the saccule by Ductus reuniens

• Utricle o lies in the posterior part of bony vestibule. o It receives the five openings of the three semicircular ducts. o It is also connected to the saccule through utriculosaccular

duct. o sensory epithelium of the utricle is called the macula

• Sacculeo Lies anterior to urticle o sensory epithelium of the saccule is called the maculao Responds to linear acceleration and decelerationo In Meniere’s disease –distented saccule lies against stapes

foot plate

• Semicircular ducts. o three in number and correspond exactly to the three

bony canals. o They open in the utricle. o The ampullated end of each duct contains a thickened

ridge of neuroepithelium called crista ampullaris.

• . Endolymphatic duct and sac. o the union of two ducts, one each from the saccule and

the utricle. o It passes through the vestibular aqueduct. o Its terminal part is dilated to form ENDOLYMPHATIC SAC

which lies between the two layers of dura on the posterior surface of the petrous bone.

Fluid System• Perilymph

o Present in btw memb. Labyrinth and bony labyrintho Present in inside the scala vestibuli and Scala tympani o Rich in sodium (Na+)o Like extra cellular fluido It communicates with CSF through the aqueduct of

cochlea.o Formation of perilymph:

• It is a filtrate of blood serum and is formed by capillaries of the spiral ligament

• a direct continuation of CSF and reaches the labyrinth via aqueduct of cochlea.

• Endolympho fills the membranous labyrinth o resembles intracellular fluid, o rich in Potassium (K+) ions. o It is secreted by

• secretory cells of the stria vascularis of the cochlea • the dark cells (present in the utricle and the

ampullated ends of semicircular ducts) .

Composition of inner ear fluids

ORGAN OF CORTI• Organ of hearing,• Situated on basilar membrane of cochlea

• 3 partso Sensory Hair cellso Supporting cellso Tectorial Membrane

Hair Cells• Transduce sound energy to Electrical Energy.• 1 row of flask shaped inner hair cells • 3 or 4 rows of cylindrical shaped outer hair cells.• Situated around the tunnel of corti

Inner Hair cells Outer Hair cells

• Total No : 3500• Arranged in single row• Flask shaped• 95% afferent from

Cochlear nerve (8th CN)• Stereocilia arranged in

V or W format• More resistent• Transmit auditory

stimuli

• 12,000 [ 1:4 ratio]• Multiple rows• Cylindrical• Efferent from Sup.

Olivary complex• Stereo cilia single

continous layer.• Easily damaged to

drugs & loud sound• Modulate the IHC.

Supporting cells

• Stabilize and support the organ of corti• Supply nutrient to the highly specialized sensory

cells(inner and outer hair cells)• Includes

o Hensen's Cell o Claudius Cells o Deiters Cellso Boettcher’s Cell

Tectorial Membrane

• It over hangs the organ of corti• Gelatinous – Spread over the hair cells.• The shearing force between Hair cells and

Tectorial membrane produces the stimulus in hair cells.

Cristae Crista Ampullaris

• Seen in the ampullated end of 3 SCC

• thickened ridge - covered by a gelatinous matrix called Cupula

• Two type of hair cells• Type 1 – Flask shaped• Type 2 – Cylindrical

• The cilia of sensory hair cells are present in cupula.

Maculae• Located in otolith organs• Sense the position of Head in

response to gravity• Hair cells

• Type 1• Type 2

• Supporting cells

• Otolithic membrane• Gelatinous layer

• Otoconia [Ca(CO3)2]• Cilia of hair cells in gelatinous

layer – Senses linear, gravitational & head tilt movements.

•

Ant. Inferior Cerebellar Art

Labyrinthine/Internal Auditory

art.

Ant. Vestibular

A(to utricle &

LSCC, SSCC)

CommonCochlear

VestibuloCochlear

Main Cochlear80%

Cochlear branch(20%)

Post. Vestibular A

(to saccule & PSCC)

Blood SupplyArterial

Venous Drainage

• 3 Veinso Internal auditory veino Vein of cochlear aqueducto Veins from the vestibular aqueduct

Applied Anatomy Presbycusis

o Sensory hearing loss associated with physiological ageing process in ear.

o 4 Pathological type• Sensory-degenaration of organ of corti• Neural-degenartion of spiral ganglion• Straial-Atropy of stria vascuaris• Cochlear-Stiffing of Basilar membrane

Noise induced hearing losso Damages the Hair cell-outer hair cells are affected more

Ototoxicityo Damage inner ear and cause SNHL,Tinnitus and vertigo.o Aminoglycoside-destroy type-1 hair cell in crista Ampularis

and outer hair cells.o Diuretics-edema and cystic changes in stria Vascularis.o Quinine-causes vasoconstriction of small vessels of cochlea

and stria vascularis.o NSAIDs-Piroxicam,KetorolacMeniere’s disease(Endolymphatic Hydrops)o Endolymphatic distention mainly in scala media,saccule,Utricleo Leads to bulging of Reissner’s Membrane and saccule and

utricle.

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