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 Human Morphology and Developmental Biology
2nd year 1st semester
Katalin Kocsis
06/11/2014

2. Inner ear

3. INNER EAR
LABYRINTHUS
INNER ACOUSTIC MEATUS

4. Inner ear Auris interna -labyrinthus osseus -labyrinthus membranaceus
-n. vestibulocochlearis végelágazódásai
-ggl. vestibulare + ggl. spirale

5. FENESTRA OVALIS
FENESTRA ROTUNDA

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

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

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

10. (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

11. 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

12. Vestibular system

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

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

15. MACULAE AND CRISTAE
Crista ampullaris
Macula utriculi

16. 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.

17. 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

18. 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

19. DISPLACEMENT OF VESTIBULAR SENSORY HAIRS

20. INNERVATION OF HAIR CELLS

21. BIPOLAR NEURONS *
myelin sheath

22. FIRST ORDER COCHLEAR AND VESTIBULAR NEURONS

23. 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

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

25. 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

27. Corti organ

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

29. Ductus cochlearis

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

31. GANGLION SPIRALE N

32. Corti-organ
Human Corti-organ

33. 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

34. 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

35. 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

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

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

38. 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

39. SUPPORTING CELLS Pillar and phalangeal cells:
extensive cytoskeletal system:
actin microfilaments
intermediate filaments
microtubules
junctional complexes
provide rigid scaffolding
to reticular lamina

40. 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

41. RETICULAR LAMINA

42. FLUID SPACES Endolymph: scala media - stereocilia
Perilymph (corti-lymph):
tunnel of Corti
spaces of Nuel
outer tunnel
- bodies of hair cells

43. BASILAR MEMBRANE Localization: tympanic lip – spiral ligament Parts:
zona arcuata
zona pectinata
Structure:
radial fibers:
collagen (Type IV)
matrix:
fibronectin
laminin
usherin – specific

44. 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

45. 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

46. 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)

47. 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

48. 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

49. 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

50. 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

51. 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

52. 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

53. 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

54. 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

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

56. 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

57. 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

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

60. 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

61. 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.

62. 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.

63. Development of ear

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

66. 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

67.                            
                                          
Otic placod
embryonic day

68. DEVELOPMENT
Inner ear

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

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

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

72. 6-9. embryonic week

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

74. inner ear development

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

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

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

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

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

81. devbio8e-fig jpg

83. DEVELOPMENT
Middle ear

84. 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

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

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

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

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

89. Hearing loss

90. 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

91. HEARING LOSS
Types:
conductive hearing loss
sensorineural hearing loss

92. 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

93. 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

94. 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

95. 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