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Inner ear. Organ of Corti. Auditory and vestibular pathways.

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1 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 Anatomy, Histology and Embryology 2nd year 1st semester Katalin Kocsis 03/11/2016

2 Inner ear

3 INNER EAR LABYRINTHUS INNER ACOUSTIC MEATUS

4 Auris interna Labyrinthus
Labyrinthus osseus Perilympha Vestibulum Canales semicirculares (ant., post., lat.) Cochlea Labyrinthus membranaceus Endolympha Utriculus Sacculus Ductus semicirculares (ant., post., lat.) Ductus cochlearis

5 Inner ear Auris interna -labyrinthus osseus -labyrinthus membranaceus
-n. vestibulocochlearis nerve endings -ggl. vestibulare + ggl. spirale

6 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

7 Labyrinthus osseus Crus osseum commune Ampullae ossei
(lat.,ant., post.) Fenestra vestibuli Blood supply: A. meningea media, A. pharyngea asc. A. carotis interna Crus osseum simplex Fenestra cochleae

8 Labyrinthus osseus Canalis semicircularis ant. Recessus ellipticus
(Utriculus) Canalis semicircularis lateralis Recessus sphericus (Sacculus) Canalis semicircularis post. Cochlea Öffnung des Aqueductus vestibuli (Ductus endolymphaticus) Crista vestibuli Recessus cochlearis

9 Labyrinthus membranaceus
Saccus endolymphaticus Ductus endolymphaticus Ductus semicircularis ant. Aqueductus vestibuli Vestibulum Ductus semicircularis post. Ductus cochlearis Ductus semicircularis lat. Sacculus Ductus reuniens Ductus utriculosaccularis Canaliculus cochleae

10 MEMBRANEOUS LABYRINTH
endolymphatic duct saccule ductus reuniens semicircular ducts cochlear duct utricule

11 SPECIALIZED NEUROEPITHELIA IN THE MEMBRANEOUS LABYRINTH
Orange = kinetic receptors Green = static receptors Red = Corti-organ

12 BLOOD SUPPLY OF THE LABYRINTH
spiral art. vestibulocochlear art. com. cochlear art → ant. vestibular labyrinthine artery →

13 Fundus meatus acusticus internus
Area nervi facialis Area vest. sup. (N. utriculoampullaris) Crista transversa Area cochleae Area vest. inf. (N. saccularis) Foramen singulare (N. ampullaris post.) Ganglion vestibulare: fundus meatus acustici interni

14 (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

15 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

16 Vestibular system

17 INFORMATIONS USED BY THE CENTRAL NERVOUS SYSTEM
TO MAINTAIN THE EQUILIBRIUM 1. Visual informations 2. Informations from proprioceptiv nerve endings 3. Vestibular informations

18 FUNCTIONS OF THE VESTIBULAR SYSTEM
PERCEPTION OF MOVEMENT AND ORIENTATION IN SPACE 2. TO MAINTAIN THE EQUILIBRIUM

19 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

20 MACULAE AND CRISTAE Crista ampullaris Macula utriculi

21 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

22 Crista ampullaris

23 Crista ampullaris Ampullopetal bending: depolarisation
Ampullofugal bending: hyperpolarisation

24 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

25 Macula Otoconia

26 DISPLACEMENT OF VESTIBULAR SENSORY HAIRS

27 INNERVATION OF HAIR CELLS

28 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.

29 BIPOLAR NEURONS * myelin sheath

30 FIRST ORDER COCHLEAR AND VESTIBULAR NEURONS

31 COMPOSITION OF THE VESTIBULAR PATHWAY
Vestibulocerebellar connections Medial longitudinal fascicle Vestibulospinal tract Reticular formation – parasympathetic nuclei Reticulospinal tract Vestibulocortical projection

32 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

33

34 Corti organ

35 COCHLEAR DUCT Position: spiral course in the cochlea blind ends:
vestibular end cupular end connected to saccule by ductus reuniens length: ~3.5 mm

36 COCHLEAR DUCT Shape: triangular Walls: stria vascularis
vestibular membrane basilar membrane: spiral limbus spiral ligament Organ of Corti

37 Ductus cochlearis

38 GANGLION SPIRALE N

39 Corti-organ Human Corti-organ

40 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 middle tunnel (Nuel's space) outer tunnel

41 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

42 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

43 HAIR BUNDLE Stereocilia of inner hair cells: 50-70
in 2 rows – longer outside flat U-shaped not embedded in tectorial membrane

44 HAIR BUNDLE Stereocilia of outer har cells: 100-300
in 3 rows – longer outside V- or W-shaped directly coupled to tectorial membrane

45 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

46 SUPPORTING CELLS Pillar and phalangeal cells:
extensive cytoskeletal system: actin microfilaments intermediate filaments microtubules junctional complexes provide rigid scaffolding to reticular lamina middle tunnel (Nuel's space) outer tunnel

47 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

48 RETICULAR LAMINA

49 FLUID SPACES Endolymph: scala media - stereocilia
Perilymph (corti-lymph): tunnel of Corti spaces of Nuel outer tunnel - bodies of hair cells middle tunnel (Nuel's space) outer tunnel

50 BASILAR MEMBRANE Localization: tympanic lip – spiral ligament Parts:
zona arcuata zona pectinata Structure: radial fibers: collagen (Type IV) matrix: fibronectin laminin usherin – specific middle tunnel (Nuel's space) outer tunnel

51 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 middle tunnel (Nuel's space) outer tunnel

52 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

53 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)

54 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

55 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

56 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

57 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

58 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

59 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

60 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

61 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

62 CENTRAL AUDITORY PATHWAY
Acoustic radiation Brachium of inferior colliculus Lateral lemniscus Trapezoid body

63 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

64 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

65

66 EFFERENT COCHLEAR NERVE FIBERS
Lateral olivocochlear efferents: Origin: lateral superior olivary nucleus Termination: inner hair cells – indirect Laterality: ipsilateral Role: set sensitivity

67 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

68

69 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.

70 Tonotopia higher pitch Membrana basilaris lower pitch

71 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.

72 Development of ear

73 Development of ear 4th week Inner ear - ectodermal origin
Middle ear - entodermal origin Auditory ossicles are from neural crest Outer ear - ectodermal origin

74

75 DEVELOPMENT Inner ear Otic placod: thickening of ectoderm: induced by
1. notochord 2. paraxial mesoderm 3. rhombencephalon Otic pit: invagination: influenced by FGF-3 Otic vesicle / otocyst: separation from surface

76                                                                        Otic placod embryonic day

77 DEVELOPMENT Inner ear

78 DEVELOPMENT Inner ear Otic vesicle: elongation into:
ventral saccular part dorsal utricular part: endolympatic duct

79 Ventral: sacculus andductus cochlearis
Dorsal: utriculus, ductus endolymphaticus -36. day

80 DEVELOPMENT Inner ear Cochlear duct: tubular outgrowth from saccule
controlled by Pax-2

81 6-9. embryonic week

82 DEVELOPMENT Inner ear Semicircular ducts:
disc-like diverticula from utricle → fusion of central parts → disappearance of central parts controlled by Nkx5

83 inner ear development

84 DEVELOPMENT Inner ear Otic capsule: 1. cartilage 2. ossification

85 DEVELOPMENT Middle ear Pharyngeal arches
outer pharyngeal grooves: ectoderm inner pharyngeal pouches: endoderm

86 Middle ear development
auditory ossicles develop from neural crest cells of the 1st and 2nd branchial arches

87 Structures in embryonic branchial arches reorganize
II. III. IV. Structures in embryonic branchial arches reorganize to form cartilages, nerve, muscles & arteries in fetus

88 DEVELOPMENT Middle ear Tympanic cavity:
lateral part of 1st pharyngeal pouch Auditory tube medial part of 1st pharyngeal pouch

89

90 devbio8e-fig jpg

91

92 DEVELOPMENT Middle ear

93 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

94 DEVELOPMENT Middle ear Tympanic membrane:
ectodermal epithelium of 1st pharyngeal groove endodermal epithelium of 1st pharyngeal pouch intermediate mesenchyme (connective tissue)

95 DEVELOPMENT External ear External acoustic meatus:
from epithelium of 1st pharyngeal groove

96 DEVELOPMENT External ear Auricle:
3 mesenchymal proliferation of 1st pharyngeal arch 3 mesenchymal proliferation of 2nd pharyngeal arch

97 Outer ear - auricle The auricle is from the first and second branchial arch ectoderm.

98 Hearing loss

99 loud noise damage on hair cells (over 100 dB)

100 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

101 HEARING LOSS Types: conductive hearing loss sensorineural hearing loss

102 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

103 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

104 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

105 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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