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Inner ear. Organ of Corti. Auditory and vestibular pathways.
Development of the auditory and vestibular apparatuses. Clinical anatomy of the auditory and vestibular systems. Semmelweis University, Faculty of Medicine Department of Human Morphology and Developmental Biology 2nd year 1st semester Katalin Kocsis 06/11/2014
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Inner ear
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INNER EAR LABYRINTHUS INNER ACOUSTIC MEATUS
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Inner ear Auris interna -labyrinthus osseus -labyrinthus membranaceus
-n. vestibulocochlearis végelágazódásai -ggl. vestibulare + ggl. spirale
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FENESTRA OVALIS FENESTRA ROTUNDA
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RIGHT OSSEUS LABYRINTH
canalis semicircularis anterior A recessus sphericus CSC recessus ellipticus A canalis semicircularis posterior cupula cochleae CS canalis semicircularis lateralis COCHLEA A fenestra vestibuli basis cochleae VESTIBULUM LATERAL ASPECT
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MEMBRANEOUS LABYRINTH
endolymphatic duct saccule ductus reuniens cochlear duct semicircular ducts utricule
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SPECIALIZED NEUROEPITHELIA IN THE MEMBRANEOUS LABYRINTH
Orange = kinetic receptors Green = static receptors Red = Corti-organ
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BLOOD SUPPLY OF THE LABYRINTH
spiral art. vestibulocochlear art. com. cochlear art → ant. vestibular labyrinthine artery →
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(tractus spiralis foraminosus)
FUNDUS OF INTERNAL ACUSTIC MEATUS anterior posterior Facial area Superior vestibular area Transvers crista Inferior vestibularis area Singular foramen Cochlear area (tractus spiralis foraminosus) Medial aspect
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STRUCTURES PASSING THROUGH THE FUNDUS
Facial area : facial nerve and n. intermedius Cochlear area (tractus spiralis foraminosus): cochlear nerve labyrithine art. and vein Sup. vestibular area: utriculoampullar nerve Inf. vestibular area: saccular nerve Foramen singulare: posterior ampullar nerve
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Vestibular system
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FUNCTIONS OF THE VESTIBULAR SYSTEM
PERCEPTION OF MOVEMENT AND ORIENTATION IN SPACE 2. TO MAINTAIN THE EQUILIBRIUM
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INFORMATIONS USED BY THE CENTRAL NERVOUS SYSTEM
TO MAINTAIN THE EQUILIBRIUM 1. Visual informations 2. Informations from proprioceptiv nerve endings 3. Vestibular informations
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MACULAE AND CRISTAE Crista ampullaris Macula utriculi
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STATIC RECEPTORS FUNCTION?
HOW DO KINETIC AND STATIC RECEPTORS FUNCTION? Kinetic receptors detect the movement of head. They respond to angular acceleration. Static receptors detect position of the head. They respond to linear acceleration.
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SCHEMATIC ILLUSTRATION AND HISTOLOGICAL APPEARANCE OF
CRISTA AMPULLARIS cupula epithelium of semicircular duct neurosensory epithelium kinocilium stereocilia type I hair cell septum with nerve fibers type II hair cell supporting cell
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of endolymphatic space
SCHEMATIC ILLUSTRATION OF MACULA UTRICULI otoconia Epithelial lining of endolymphatic space Otolith membrane Epithelium Scanning EM image of otoconia Type I. haircell with cupshaped afferent nerve ending Type II. haircell with bouton- like afferent nerve ending
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DISPLACEMENT OF VESTIBULAR SENSORY HAIRS
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INNERVATION OF HAIR CELLS
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BIPOLAR NEURONS * myelin sheath
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FIRST ORDER COCHLEAR AND VESTIBULAR NEURONS
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VESTIBULAR PATHWAY Function of medial longitudinal fascicle
To coordinate the conjugate eye movement with movement of head and neck and maintain the visual fixation Lat. semic. duct Axial muscles
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COMPOSITION OF THE VESTIBULAR PATHWAY
Vestibulocerebellar connections Medial longitudinal fascicle Vestibulospinal tract Reticular formation – parasympathetic nuclei Reticulospinal tract Vestibulocortical projection
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SIGNIFICANCE OF VARIOUS PARTS OF THE VESTIBULAR SYSTEM
1. Innervation of muscles assisting to maintain the equilibrium 2. Coordination of conjugate eye movement with the movement of the head and to maintain the visual fixation 3. Regulation of muscle tone and on this way to maintain the balance 4. Vestibular stimulation may provoke visceral responses 5. Cortical representation helps the realization of movements
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Corti organ
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COCHLEAR DUCT Position: spiral course in the cochlea blind ends:
vestibular end cupular end connected to saccule by ductus reuniens length: ~3.5 mm
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Ductus cochlearis
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COCHLEAR DUCT Shape: triangular Walls: stria vascularis
vestibular membrane basilar membrane: spiral limbus spiral ligament Organ of Corti
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GANGLION SPIRALE N
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Corti-organ Human Corti-organ
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ORGAN OF CORTI Cell types: sensory cells: inner hair cells
outer hair cells supporting cells: border cells inner phalangeal cells inner pillar cells outer pillar cells outer phalangeal cells (Deiters’ cells) Hensen’s cells Claudius’ cells
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INNER HAIR CELLS Shape: pear-shaped Localization: in 1 row
surrounded by inner phalangeal cells Number: ~3 500 Apical surface: cuticular plate stereocilia – hair bundle Basal surface: synapses with afferent fibers
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OUTER HAIR CELLS Shape: long cylindrical Localization: in 3 (4-5) rows
in cup-shaped upper ends outer phalangeal cell bodies, lateral side is free Number: ~15 000 Apical surface: cuticular plate stereocilia – hair bundle Basal surface: synapses wtih afferent fibers with efferent fibers
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HAIR BUNDLE Stereocilia of inner hair cells: 50-70
in 2 rows – longer outside flat U-shaped not embedded in tectorial membrane
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HAIR BUNDLE Stereocilia of outer har cells: 100-300
in 3 rows – longer outside V- or W-shaped directly coupled to tectorial membrane
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STEREOCILIA Ultrastructure: actin filaments
cross-links (fimbrin, espin) myosin (VI, VIIa – specific, XVa) stereocilia taper at their bases: diminishing actin filaments actin filaments extend into the cuticular plate – cuticular plate: rigid platform formed by a meshwork of actin filaments Interciliary links: tip link (cadherin 23) lateral links Mechanical features: stereocilia respond as a unit move as rigid rods pivoting at their insertion
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SUPPORTING CELLS Pillar and phalangeal cells:
extensive cytoskeletal system: actin microfilaments intermediate filaments microtubules junctional complexes provide rigid scaffolding to reticular lamina
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RETICULAR LAMINA Structure:
stiff mosaic of apical domains of hair cells and supporting cells junctional complexes: tight junction zonula adherens Components: apical part of hair cells (cuticular plate) apical parts of supporting cells: inner phalanges head plates of inner pillar cells head plates of outer pillar cells outer phalanges Function: stiff mechanical support for hair cells seal between fluid spaces
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RETICULAR LAMINA
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FLUID SPACES Endolymph: scala media - stereocilia
Perilymph (corti-lymph): tunnel of Corti spaces of Nuel outer tunnel - bodies of hair cells
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BASILAR MEMBRANE Localization: tympanic lip – spiral ligament Parts:
zona arcuata zona pectinata Structure: radial fibers: collagen (Type IV) matrix: fibronectin laminin usherin – specific
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TECTORIAL MEMBRANE Localization:
attached to the interdental cells of vestibular lip (cuticule) overlie the organ of Corti stereocilia of the outer hair cells are attached to it not the stereocilia of the inner hair cells – Hensen’s stripe Structure: radial fibers: collagen (Types II, V, IX) matrix: otogelin – specific tectorin – specific
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HEARING Role of the ear: mechanotransduction:
conversion of mechanical stimulus (sound waves) into electrical signal Sound transduction: vibration of tympanic membrane ↓ vibration of stapes: amplification pressure waves of perilymph displacement of basilar membrane
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HEARING Sound transduction: displacement of basilar membrane ↓
shear between: hair cells and tectorial membrane bending of stereocilia: outer hair cells: direct inner hair cells: indirect (or direct)
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HEARING Role of hair cells: bending of stereocilia → electrical signal
detection of <1 nm displacement: importance of rigidity A: lateral bending of stereocilia opening of cation channels ↓ K+ (Ca++) influx depolarization → opening of voltage-sensitive Ca++ channels release of neurotransmitter (glutamate) triggering action potential in afferent fiber B: medial bending of stereocilia decrease in cation channel conductance hyperpolarization
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SIGNIFICANCE OF FLUID SPACES
K+ Potencial Perilymph (corti-lymph) 5 mM 0 mV Endolymph mM + 80 mV Hair cell 130 mM - 70 mV 150 mV electrical driving force for K+ and Ca++ Maintenance of low K+ concentration in corti-lymph: supporting cells → cells of spiral ligament → cells of stria vascularis: removal of K+ from hair cells essential role of gap junctions: connexin 26 Endolymph (K+) secretion: stria vascularis
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CHARACTERISTICS OF HEARING
Encoding of frequency: Structure of basilar membrane: narrow (100 μm) and stiff at the base (thick fibers) wide (500 μm) and slack at the apex (thin fibers) Frequency analyzer: position of peak amplitude of basilar membrane determined by stimulus frequency high frequency → maximal near the base low frequency → maximal near the apex Tonotopic map of organ of Corti
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CHARACTERISTICS OF HEARING
Encoding of sound intensity: displacement amplitude of basilar membrane ↓ displacement amplitude of stereocilia → level of depolarization of hair cells → frequency of action potentials number of activated hair cells → number of activated afferent fibers
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COCHLEAR NERVE FIBERS Afferent fibers:
bipolar neurons of spiral ganglion: ~30 000 90-95%: Type I (large) 5-10%: Type II (small) Type I ganglion cell: contacts inner hair cell 1 hair cell → ~10 ganglion cells divergence Type II ganglion cell: contacts outer hair cells 1 ganglion cell ← ~10 hair cells convergence
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COCHLEAR SIGNAL TRANSDUCTION
Inner hair cells: provide major input to auditory centers Outer hair cells: modulatory role Tonotopy: height of cells: μm height of stereocilia: μm number of stereocilia number of ion channels – size of currents
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COCHLEAR SIGNAL TRANSDUCTION
Role of outer hair cells: somatic motor: length changes of cells are synchronized with basilar membrane vibration → amplification of basilar membrane vibration in a frequency-specific manner prestin hair bundle motor ↓ Cochlear amplifier: at high frequency increases sensitivity selectivity
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CENTRAL AUDITORY PATHWAY
Medial geniculate body Inferior colliculus Nucleus of the lateral lemniscus Ventral cochlear nucleus Superior olivary nucleus Dorsalis cochlear nucleus Nucleus of trapezoid body
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CENTRAL AUDITORY PATHWAY
Acoustic radiation Brachium of inferior colliculus Lateral lemniscus Trapezoid body
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CENTRAL AUDITORY PATHWAY
Neurons: 1. spiral ganglion 2. ventral cochlear nucleus (dorsal cochlear nucleus) 3. superior olivary nucleus (nucleus of trapezoid body) 4. inferior colliculus (nucleus of the lateral lemniscus) 5. medial geniculate body 6. primary auditory cortex (Brodmann’s areas 41, 42) Bilateral pathway Tonotopic organization of the entire auditory pathway: isofrequency laminae isofrequency columns
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CENTRAL AUDITORY PATHWAY
Superior olivary nucleus: receives cochlear fibers from both sides Localization of the origin of sound: ipsilateral efferent fibers: inhibitory contact lateral dendrites contralateral efferent fibers: excitatory contact medial dendrites
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EFFERENT COCHLEAR NERVE FIBERS
Lateral olivocochlear efferents: Origin: lateral superior olivary nucleus Termination: inner hair cells – indirect Laterality: ipsilateral Role: set sensitivity
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EFFERENT COCHLEAR NERVE FIBERS
Medial olivocochlear efferents: Origin: nucleus of trapezoid body, medial superior olivary nucleus Termination: outer hair cells – direct Laterality: ipsi- and contralateral Role: inhibition of cochlear amplifier
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He attended courses at universities of different countries,
GYÖRGY BÉKÉSY (Budapest, junius Honolulu, junius 13.) He attended courses at universities of different countries, but he received his diplome in Budapest. He carried out his research work with his very precise methods at the Experimental Department of Hungarian Post Company. In 1939 he was appointed as a full-time professor at the University of Natural Sciences. In the same year he became the member of Hungarian Academy of Sciences. He left Hungary in 1946 for Stockholm, then the Harvard University. He received Nobel-Price in 1961 for the discovery of physical mechanism causing excitation in the cochlea.
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THE MECHANISM OF AUDITION
(HOW IS THE FLUID VIBRATION CONVERTED INTO THE NERVE IMPULSE) Ext. a. m. Footplate of stapes Helicotrema Scala vestibuli Cochlear duct Basilar membrane Scala tympani Cavum tympani The pitch of voice is determined by the frequency of vibration, the intensity is determined by the amplitude of vibration. Discrimination of pitch and intensity of voice occur in the cochlea.
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Development of ear
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Development of ear 4th week Inner ear - ectodermal origin
Middle ear - entodermal origin Auditory ossicles are from neural crest Outer ear - ectodermal origin
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DEVELOPMENT Inner ear Otic placod: thickening of ectoderm: induced by
1. notocord 2. paraxial mesoderm 3. rhombencephalon Otic pit: invagination: influenced by FGF-3 Otic vesicle / otocyst: separation from surface
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Otic placod embryonic day
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DEVELOPMENT Inner ear
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DEVELOPMENT Inner ear Otic vesicle: elongation into:
ventral saccular part dorsal utricular part: endolympatic duct
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Ventral: sacculus andductus cochlearis
Dorsal: utriculus, ductus endolymphaticus -36. day
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DEVELOPMENT Inner ear Cochlear duct: tubular outgrowth from saccule
controlled by Pax-2
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6-9. embryonic week
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DEVELOPMENT Inner ear Semicircular ducts:
disc-like diverticula from utricle → fusion of central parts → disappearance of central parts controlled by Nkx5
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inner ear development
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DEVELOPMENT Inner ear Otic capsule: 1. cartilage 2. ossification
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DEVELOPMENT Middle ear Pharyngeal arches
outer pharyngeal grooves: ectoderm inner pharyngeal pouches: endoderm
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Middle ear development
auditory ossicles develop from neural crest cells of the 1st and 2nd branchial arches
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Structures in embryonic branchial arches reorganize
II. III. IV. Structures in embryonic branchial arches reorganize to form cartilages, nerve, muscles & arteries in fetus
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DEVELOPMENT Middle ear Tympanic cavity:
lateral part of 1st pharyngeal pouch Auditory tube medial part of 1st pharyngeal pouch
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devbio8e-fig jpg
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DEVELOPMENT Middle ear
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DEVELOPMENT Middle ear Ossicles:
malleus (anterior lig. of malleus) and incus: from 1st pharyngeal arch cartilage stapes: from 2nd pharyngeal arch cartilage ossicles remain embedded in mesenchyme until the 8th month Muscles: tensor tympani: from 1st pharyngeal arch stapedius: from 2nd pharyngeal arch
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DEVELOPMENT Middle ear Tympanic membrane:
ectodermal epithelium of 1st pharyngeal groove endodermal epithelium of 1st pharyngeal pouch intermediate mesenchyme (connective tissue)
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DEVELOPMENT External ear External acoustic meatus:
from epithelium of 1st pharyngeal groove
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DEVELOPMENT External ear Auricle:
3 mesenchymal proliferation of 1st pharyngeal arch 3 mesenchymal proliferation of 2nd pharyngeal arch
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Outer ear - auricle The auricle is from the first and second branchial arch ectoderm.
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Hearing loss
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CHARACTERISTICS OF HEARING
Threshold: 20 μPa Dynamic range: 0-140 dB (7 orders of magnitude) Frequency range: Hz Frequency discrimination: >2000 pitch levels 0.2% frequency difference
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HEARING LOSS Types: conductive hearing loss sensorineural hearing loss
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CONDUCTIVE HEARING LOSS
External ear: blockage of external acoustic meatus Middle ear: disruption of tympanic membrane fluid build-up in tympanic cavity destruction of ossicles fixation of stapes in oval window Conductive hearing loss: maximum 60 dB
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SENSORINEURAL HEARING LOSS
Inner ear or auditory pathway: damage in organ of Corti: acute or chronic noise trauma infection hypoxia damage of innervation Sensorineural hearing loss: can be total
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SENSORINEURAL HEARING LOSS
Deafness genes: stereocilia: myosin VI, VIIa, XVa cadherin 23 outer hair cells: prestin inner hair cells: otoferlin supporting cells connexin 26 of gap junctions basilar membrane: collagen Type IV usherin tectorial membrane: tectorin otoancorin
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REFERENCES Carlson, B.M. Human embryology and Developmental Biology. 1994 Moore, K.L. The developing human. 1988 Szentágothai, J; Réthelyi Miklós. Funkcionális anatómia. 2002 Röhlich, P. Szövettan. 2006 Rohen, J.W.; Yokochi, C; Lütjen-Drecoll, E. Color atlas of Anatomy Törő, I. Szövettan. 1967 Junqueira, L.C.; Carneiro, J.; Kelley, R.O. Basic histology. 1989 Moore, K.L. Clinically oriented anatomy. 1980
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