ANATOMY OF THE INNER EAR

Dr(Prof) Rahul Kawatra(HOD) Dr Mohd Shakeel (Guide)

Dr Satveer Singh J1

DEVELOPMENT OF INNER EAR

• First part to appear is the inner ear• PLAC0DES CALLED OTIC PLACODES DEVELOP FROM

GERMINATIVE EPITHELIUM AROUND 22nd days OF EMBRYO• PLACODE FORMS OTIC CYST or OTIC VESCICLE• Otic vesicle immerses and is surrounded by mesenchyme to

form the otic capsule• SACULE IS THE FIRST TO APPEAR,THEN COCHLEAR duct,(6th

week),ductus Reunion, three CAVITIES SCALA MEDIA,SCALA TYMPANI,SCALA VESTIBULI,PERILYMNP,ENDOLYPH and ORGAN OF CORTI

DEVELOPMENT OF INNR EAR

LABYRINTH

• LABYRINTH or INNER EAR EAR

• Consists of two parts

• Bony labyrinth

• Membranous labyrinth

INNER EAR

The inner ear consists of a membranous labyrinth

encased in an osseous labyrinth

BONY LABYRINTH

• It is composed of a system of bony tubes and chambers located in the petrous portion of the temporal bone

• And with in the bony labyrinth ,is a system of membranous tubes and chambers called the membranous labyrinth

• Perilymph similar to csf fills the space between bony and membranous labyrinth

• Perilymph rich in sodium ions

INNER EAR

• Cochlea

• Snail shaped bony structure

• Contains endolymph and perilymph

• Auditory fluids that aid in transmission of sound vibrations

Auditory transduction takes place in the inner ear

Transduction refers to the transformation of energy from one form to another .In the case of ear ,acoustic (mechanical)energy is transformed to electrical energy

EAR

PARTS OF INNER EAR

VESTIBULE AND COCHLEA

• The vestibule and semicircular canals are concerned with vestibular functions(balance)

• The cochlea is concerned with hearing

• The oval and round window open into the vestibule at the base of the cochlea

THE COCHLEAThe cochlea is a coiled tube

It is coiled around the modiolus

The base of cochlea is opposite the promontory

Oval and round window open into vestibule

COCHLEA UNCOLILED

COCHLEA

Reissner membrane and the basilar membrane divide the cochlea longitudinally into three scalae; Scala media

Scala vestibuli

Scala tympani

SPIRAL ORGAN

CROSS SECTION OF THE COCHLEAR DUCT

If you cut the cochlear tube crossectionally.

You would see something like this.Scala vestibuli on the top.

Scala tympani on the bottom and

Scala media is a triangular duct in the middle

ORGAN OF CORTI

Scala media is more or less triangular, formed by the reissner’membrane, basilar membrane and the structures called stria vascularisThe fluid that fills the scala tympani and scala vestibuli is called perilymph and that which fills the scala media is called endolymphOrgan of corti(spiral organ) is provided with hair cells

BASILAR MEMBRANE

• Movement of the basilar membrane by pressure changes induced in the scala tympani by stapes foot plate motion at the oval window is a critical step in the transduction process

• The organ of corti rests on the basilar membrane

ORGAN OF CORTITwo type of cellsSupporting cells such as deiter’cells support hair cellsHair cells(receptor cells) : that transduce soundThe tops of the hair cells and pillar cells form the reticular membraneThe tectorial membrane is loosely coupled to the Reticular membraneOrgan of corti transduces pressure waves to action potential

HAIR CELLS• Four rows of hair cells : three outer and one

inner• Number of cells in the cochlea is

16000to20000• Hair cells have multiple projections called

steriocilia• The amplification of outer hair cells is very

sensitive to ototoxic drugs and loud noise.• Outer hair cells once destroyed ,never

recovers

STEROCILIASTERIOCILIA ON INNER AND OUTER HAIR CELLS

ARE ARRANGED IN A CURVED Or V SHAPED

ROWS THAT FACE TOWARD THE MODIOLUS

FREQUENCY REPRESENTATION

CUT SECTION OF THE COCHLEA

COCHLEAR NERVE

HAIR CELLSAfferent fibres (that go to the brain) innervate the inner hair cellsEfferent fibres innervate the outer hair cellsInner hair cells are sensory cells responsible for 95% information to the brainOuter hair cells are motor cells that ampliphy the movements of the basilar membrane in response to a stimulusSome of this energy is transmitted back to middle ear which can be recorded as otoacoustic emission

CENTRAL AUDITORY PATHWAY

Cochlear nerve from cochlea to cochlear nucleus in brain stemAuditory nerve splits into two streams red which go to the ventral cochlear nucleusGreen go to the dorsal neucleus

CENTRAL AUDITORY PATHWAYFrom the ventral nucleus to the superior colliculus and inferior colliculus through the lateral lemniscus then to medial geniculate body and to auditory cortex in temporal lobeMinute differences in timing and loudness in each ear is localised by dorsal cochlear nucleus

AUDITORY PATHWAY

From dorsal nucleus directly to thalamus and cortex

Analyse the quality of sound, picking apart the tiny frequency differences

Efferent are derived from the superior coliculus and make direct connection with outer hair cells

VESTIBULAR SYSTEMThree semicirular ducts and otolith organsThree canals are at right angles to each otherRepresent three axes of rotation VerticalAnterioposteriorTrnsverse

SEMICIRCULAR CANALS

• Named according to their position1 anterior or superior canal2 Posterior canal3 Lateral or horizontal or external canal

Anterior and posterior canal are verticalLateral canals of both sides are horizontal and in the

same plane at an angle of 30 degrees

SEMICIRCULAR CANALS

• When the head is bent forward about 30 degrees,the lateral semicircular canals are then approximately horizotal to the surface of earth

• The anterior canals are in vertical planes that project forward and 45 degrees outward.Where as posterior canals arealso in vertical planes but project backwrd and 45 degrees outwards

SEMICIRCULAR CANALS

AMPULLA

Two ends of canals

One enlarged called ampulla and it contains receptor organs called crista ampularis

AMUPPLA

• The ampulla of all the three canals and the narrow end of the horizontal canal open directly into the utricle

• The narrow end of the anterior and posterior canals open into the utricle jointly by forming a common crus

• Thus,semicircular canals open into the utricle by means of five openings

OTOLITH ORGAN OR VESTIBULE

• Utricle communicates with the saccule through utricular saccular duct• Saccule communicates with cochlea through ductus reunionEndolymphatic duct arises from the utricular saccular duct and it ends in a bag called endolymphatic sac which lies on the cranial surface of petrous bone• Utricle and saccule form otolith organs

CRISTA AMPULARIS

• Crest like structure inside the ampulla

• Crest formed by receptor epithelium (neuroepithelium ) which consists of hair cells, supporting cells and secreting cells

Which secrete the ground substance proteoglycanThese cells are arranged in plane semilunatum(group of

epithelial cells) around hair cells

CRISTA AMPULARIS

HAIR CELLSHair cells are the receptor cells of crista ampularis

Two types of cellsHair cells of semicircular canalSaccule and utricleReceive both Afferent and efferent nerve terminals

HAIR CELLS

Type 1 hair cells flask shapedAfferent nerve terminals surround the cell body in the form of calyx Efferent terminals end on the surface of calyx Type 2 hair cells Cylindrical or test tube shapedBoth afferent and efferent terminate without forming calyx on the cell body

CUPULAFrom crista ampularis, a Gelatinous substance Extenends up to the roof Of the ampulla known as Cupula

The cilia of hair cells are projected in to the cupula

MACULA• The receptor organs in utricle and saccule are called macula

• Like crista ampularis ,it is also formed by neuroepithelium and supporting cells

• Two type of hair cells type 1 and type 2

• Situation of macula is different in utricle and saccule

• In utricle , the macula is situated in horizontal plane so cilia of hair cells are in vertical plane

• In saccule , the macula is in vertical plane and the cilia are in horizontal plane

MACULABlankets of calcium Carbonate crystals are On the top of Gelatinous matrix Surrounding hair cells

The breakage of these crystals results in benign positional Vertigo

BLOOD SUPPLY TO VESTIBULAR END ORGANS

Anterior inferior cerebellar artery branch of basilar arteryAnterior inferior cerebellar artery divides into anterior vestibular artery and internal auditory artery

Anterior vestibular artery supplies most of utricle,superior and horizontal ampullae and small portion of saccule

NERVE SUPPLY TO VESTIBULAR APP

First order neuroneBipolar in nature

Body or soma is in the Scarpa ganglion Situated in internal Auditory meatus

NERVE SUPPLY

The dendrites of the bipolar cells reach the receptor organs in the crista ampularis and macula

The axons form the vestibular division of vestibular cochlear nerve

VESTIBULAR NEUCLEI• Four vestibular nuclei in the medulla oblongata• Superior, inferior, lateral and medial• Most of the vestibular fibres coming from crista

ampularis of semicircular canals reach superior and medial nuclei

Lateral vestibular nuclei receives the fibres mostly from the maculae of otolith organs

The inferior vestibular nuclei receives fibres from both the crista ampularis and maculae

The fibres from some bipolar cells reach cerebellum directly and terminate in the floculonodular lobe or the fastigial nucleus in the cerebellum

• The efferent fibres to hair cells provide tonic inhibition of hair cells

SECOND ORDER NEURON 1 vestibulo ocular tract This tract is concerned with movements of eyeballs in

relation to the position of the head 2vestibulo spinal tractThis tract is involved in reflex movements of head and body

during postural change 3 Vestibuloreticular tractThese fibres are concerned with facilitation of muscle tone 4 vestibulo – cerebellar tractInvolved in coordination of movement acc. To body

position

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