I nininni

:

INNER E

AR

BY

DR NITIN

THOMAS

INNER EAR DEVELOPMENT OF INNER EAR Begins : 3rd week of fetal lifeCompletes : 16th weekMembraneous & Bony labyrinth develop from otic capsule

Ectoderm in hind brain

Auditory Placode

Auditory vesicle differentiates

- Endolymphatic duct & - sac

Semicircular ducts Pars

Utricle Superior

Saccule Pars

Cochlea Inferior

INNER EAR / LABYBRINTH

BONY & MEMBRANOUS LABYRINTH seperated by PERILYMPH

ENDOLYMPH

BONY LABYRINTH VESTIBULE SEMI CIRCULAR

CANALS COCHLEA

Vestibular apparatus for balance and

equilibrium

Cochlea for hearing

A} VESTIBULE Central chamber

Lateral wall : oval window

Spherical- lodges saccule

Medial wall : 2 Recessess

Elliptical- lodges utricle

Spherical R. – has perforated holes

Maculae Cribrosa Media –

inferior vestibular nerve

Elliptical R. –

Maculae Cribrosa Superior (Mike’s spot) – “Translabyrinthe” approach

N to Utricle & ampulla

of Sup’r & lateral canals

B} SEMI CIRCULAR CANALS Lie At to each other

Rt Angles

Superior Posterior

(15-20mm) lateral (18-20mm)

(12-15mm) lie lie

transverse Parallel to petrous part of

to petrous part of temporal bone

Temporal bone

bulge into aditus & antrum

Ampullated end-opens into vestibule

Non Ampullated end of Supr & Post’r canals

Unite – common channel –

CRUS COMMUNE(4MM) C}

COCHLEASnail

Lies Antr to bony labyrinth

L=30mm

Coiled tube 2.5 - 2.75 turns around central pyramid of bone

MODILOUS – spirally –OSSEOUS SPIRAL

LAMINA

base towards Int. Acoustic Meatus transmits cochlear vessels & nerves

• Bony cochlea : 3 compartments Scala Vestibuli Scala Tympani Scala media

(Membranous cochlea)

- perilymph

- communicate via cochlea apex Endolymph

HELICOTREMA

MEMBRANOUS LABYRINTH Consists “ESCUSE”

-Endolymphatic duct

-Semi circular duct

-Cochlear duct

-Utricle

-Saccule

-Endolymphatic sac

COCHLEAR DUCT / MEMBRANOUS COCHLEA / SCALA MEDIA

• Coiled tube• Triangular on cross section• 3 walls :

Basilar memb – supports organ of corti - has sound receptors

- thin inner part ZONA ARCUATA

- thick outer part ZONA PECTINATA

- seperates Scala tympani from scala media

-its length from Basal coil (High freq sound) – Apical coil (low freq

sound)

Reissner’s membraneSeperates scala vestibuli - scala media

Stria vascularis-Vascular epith.

-Endolymph secretion

Cochlear duct connects to saccule by DUCTUS REUNIENS

Organ of corti• Spead entirely over Basilar membHas TUNNEL OF CORTI – consists of 2 rows of rods of inner & outer hair

cells1 row of inner hair cells & 3-4 rows of outer hair cellsInner rods-3500Outer rods-12000Hair cells supported by Pillar cells , Dieter cells , Hensens cells

Mechanical sound energy gets

transduced into electrochemical energy

TECTORIAL MEMBRANE • Has gelatinous matrix with fibers• Lies above Organ of corti• Its undersurface attaches to tip of outer hair cells

Shearing force b/w them stimulates hair cells

UTRICLE & SACCULEBoth lie in bony vestibule but saccule lies anterior to utricleUtricule connects to saccule via UTRICOSACCULAR DUCTCochlear duct connects to saccule via DUCTUS REUNIENSUtricle has 5 openings of 3 semicircular canalsSpherical recess-Saccule (S-S)Elleptical recess-Utricle U – lies horizontallyIts vestibular receptor organ MACULA

S- lies vertically

Linear acceleration & decelaration

Has hair cells + supporting cells + gelatinous mass

secreted by has

Mucopolysaccharides

Gelatinous mass – also contains – CaCO3 crystals

OTOLITH / STATACONIA

ENDOLYMPHATIC DUCT & SAC• Union of 2 ducts (1 from saccule and 1 from utricle) • Pass through Vestibular Aqueduct• Terminal end – dilated – forms ENDOLYMPHATIC SAC

SEMICIRCULAR DUCTS3 in numberOpen in utricleAmpullated end – has thick neuroepithelium – CRISTA AMPULLARIS

Hair cells + Supporting cells + Gelatinous mass

dome shaped In cristae

CUPULA

HAIR CELLS 2 types

type 1 type 2

(FLASK SHAPED) (CYLINDRICAL)

Summit CRISTAE Periphery

Hair cells 1 KINOCILIUM Many STEREOCILIA (60-110)

Inner hair cells – Afferent Cochlear fibers – transmit auditory impulses

Outer hair cells – Efferent fibers – modulate inner hair cells fx

Supporting cells

Dieters cell - lie in b/w outer hair cells

Outside it - Hensens cells lie

MECHANISM OF HEARING

TM Pr. Changes in

SOUND PINNA EAC Vibration of OSSICULAR CHAIN

FOOT PLATE LABYRINTHINE

OF STAPES FLUID

AUDITORY N. TRANSDUCTION STIMULATES HAIR CELLS OF BASILAR MEMB.MOVES

ORGAN OF CORTI

COCHLEAR NUCLEI - SUPR. OLIVARY COMPLEX – LAT. LEMNISCUS – INFR. COLLICULUS

AUDITORY CORTEX MEDIAL GENICULATE BODY

(AREA 41 / BROADMANN’S AREA)

BLOOD SUPPLY

LABYRINTHINE @ {Br. Of Antr Infr Cerebellar @}

common cochlear Antr Vestibular @

{Utricle , Supr & Lateral Canal}

Vestibulo cochlear Main cochlear

{ 80% Cochlea}

Cochlear br. Postr Vestibular @

{ 20% Cochlea} {Saccule ; Postr Canal}