Anatomy of Inner ear

DR YATISH KUMAR B L MS ENT PG/JR 1

Inner Ear Consists of an

irregular system of canals and cavities:

Bony labyrinth

Membranous labyrinth

Bony labyrinth: Hard, bony outer shell.

Membranous labyrinth: Fully contained inside the bony labyrinth.

Bony labyrinthVestibule – central

chamber of labyrinth. In its lateral wall lies the oval window.

Semicircular canals.

Cochlea.

Membraneous labrynth

Cochlear duct

Utricle

Saccule

Three semicircular

canals

Endolymphatic duct

and sac

UtriclePosterior part of

vestibule.5 openings of

semicirular ducts.MaculaUtricosaccular

duct.

Saccule lies anterior to

utricle opposite the

stapes footplate in

the bony vestibule.

Saccule is connected

to the cochlea via a

thin reunion duct.

Semicircular ducts3 in number.Open into utricleCrista ampularis

Crista ampullaris

Macula is a gelatinous matrix into which hair cells project and which is studded with tiny calcium carbonate granules called otoconia.

Arrangement of stereocilia

Each row of stereocilia is taller than the next. The tip of each stereocilium is linked to the side of the stereocilium behind it by a tip link.

Hair cells type 1 type ll

Types of Hair cells

Type 1 Hair cells = flask shaped cells with a rounded base, narrow neck.

Nucleus is basal, surrounded by mitochondria

With supranuclear Golgi complex, occasional cisternae of RER & small vesicles.

With 50-100 sterocilia on free surface. Tallest hair is 10um near kinocilium & shortest is 1um on the opposite side.

Type ll Hair cells = more columnar, kinocilium, sterocilia, cytoplasmic roganelles are similar to type 1.

Golgi complex is larger, small vesicles found in great numbers in cytoplasm.

Synaptic ribbons are found in the peripheral cytoplasm opposite the plasmalemma of terminal boutons.

Some endings contain clear synaptic vesicles (non granulated vesicles) carry afferent nerves info to brain.

Semicircular CanalsThree semicircular

canals- Lateral

(Horizontal)Superior

( Anterior vertical)

Posterior ( Posterior vertical)

Horizontal semicircular canalThe lateral or horiz

ontal canal (external semicircular canal) .

shortest of the three canals.

Movement of fluid within this canal corresponds to rotation of the head around a vertical axis (i.e. the neck).

Projects as rounded bulge in middle ear, aditus & antrum

Makes an angle of 30 with horizontal plane.It measures from 12 to 15 mm., and its

arch is directed horizontally backward and laterally; thus each semicircular canal stands at right angles to the other two.

Superior semicircular canal> detects rotation of

the head around a rostral-caudal (anterior-posterior) axis, or in other words rotation in the coronal plane.

> example, when you move your head to touch your shoulders.

>15 to 20 mm in length, is vertical in direction.

Its lateral extremity is ampullated, and opens into the upper part of the vestibule; the opposite end joins with the upper part of the posterior canal to form the crus commune, which opens into the upper and medial part of the vestibule.

Posterior semicircular canalThe posterior

semicircular canal detects rotations of the head in around the lateral axis. This occurs, for example, when nodding your head.

It detects rotations of the head in the sagittal plane.

Nodding of head.18 to 22 mm.

Semicircular Canals The angle formed by three semicircular canals is the

Solid angle.

Trautmann’s triangle.The triangle bounded by the bony labyrinth,

sigmoid sinus, and superior petrosal sinus is known as Trautmann’s triangle.

Cochlea

Snail shaped coiled tube.

2.5 to 2.75 turns round a central pyramid of bone called modiolus.

30 mm long

5 mm from base to apex & 9 mm around its base Anterio medial to vestibule.

Modiolus

Central pyramid of bone around which cochlea forms

The base of modiolus directed towards internal acoustic meatus

Transmits vessels and nerves to cochlea

Promontary

A bony bulge in the medial wall of middle ear , represents the basal coil of cochlea.

VestibuleCentral chamberSpherical recess-

sacculeEllipticle recess-

utricle

Osseous spiral lamina

A thin plate of bone winds spirally around modiolus .

This bony lamina gives attachment to the basilar membrane and divides the bony cochlea tube into three compartments.

Basilar membrane = thin sheet extending from spiral lamina to spiral ligament of cochlea. Movement of the the basilar membrane by pressure changes induced by stapes footplate motion at the oval window

Vestibular membrane = 2nd partition from soft tissue ridge of spiral lamina to the spiral ligament.

• Reissner’s membrane = outer surface of vestibular membrane, lined by thin squamous perilymphatic cells.

Lumen of cochlear canal is partitioned into 3 spiral chambers:1. scala vestibuli (above)2. scala media (between)3. scala tympani (below)

Rosenthal’s canal Spiral ganglions are

situated in this canal which runs along the osseous spiral lamina.

Scala vestibuli

This uppermost channel is continuous with vestibule and closed at oval window by stapes footplate

Scala tympani

This lowermost channel is closed by secondary TM of round window

Scala media

Bind coiled tube, connected to the saccule via ductus reunions.

Helicotrema

Aqueduct of cochlea Scala tympani

is connected with subarachnoid space via aqueduct of cochlea.

It is thought to regulate perilymph & pressure in bony labrynth

Basilar membrane>Has 2 zones:Zona arcuata =

thin, extends from medial attachment to base of outer most cells of organ of Corti. Supports the organ of Corti.

Zona pectinata= thicker from organ of Corti to spiral ligament.

Tectorial membraneSecreted at the

upper surface of interdental cells, forms a cuticular layer over these cells

Composed of fine filaments embedded in gelatinous matrix rich in mucopolysaccharides.

Organ Of CortiThe end organ of

hearingInner hair cells -

broad base, resting on the basilar membrane, slender and conical, nucleus is basal.

Outer hair cells -longer and more oblique, leaning to the inner pillars.with broad thin base.

Tunnel of corti- wide triangular intercellular space continuous through cochlear length. Bounded above converging inner and outer pillar cells.

Deiters cells -the supporting cells for the 3 -4 rows of outer hair cells. Base is columnar with cup shaped upper end. The apex does not reach the free surface of the organ of Corti.

Inner phalangeal cells - arranged in a row on the inner side of the inner pillar cells. Contiguous with slender Border cells marking the inner boundary of the organ of corti. Lining epithelium is low cuboidal or squamous cells.

Cells of Hensen - delimit the outer border of the organ of Corti arrange in rows decreasing in height continuous with the cells of Claudius.

A closer look at the organ of Corti

Reticular laminaThe reticular

lamina is a solid surface at the tops of the hair cells, so the tops of the hair cells are in endolymph and the bottom of the hair cells are in perilymph.

Deiter’s cells

Arrangement of hair cells

The spiral ganglionThe cell bodies of the neurons that form the auditory nerve are located within the cochlear modiolus. The collection of cell bodies is called the spiral ganglion.

Blood supply of labrynth

Venous drainage

Internal auditory vein

Vein of cochlear

aquaduct

Vein of vestibular

aquaduct

Drain into inferior petrosal and sigmoid sinuses

Internal auditory canal

About 1 cm long

Passes into

petrous part of

temporal bone in

a lateral direction

Lined by dura

At its lateral end (fundus)

IAC is closed by a vertical

cribriform plate of bone

that seperates it from

labrynth

A transverse crest divides

this plate into smaller

upper and larger lower part

Upper part is again divided

into ant & post part by a

vertical crest called BILL’S

BAR.

IAC - Contents

Vestibulocochlear Nerve

Facial nerve including nervus intermedius

Internal auditory artery and vein

Inner ear fluids

perilymph endolymph

Resembles ECF Resembles ICF

Rich in sodium ions Rich in pottasium ions

Endolymph Perilymph CSF

Na+ 5 140 152

K+ 144 10 4

Protien 126 200-400 20-50

Glucose 10-40 85 70

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