ANATOMY OF THE INNER EAR

1. ANATOMY OF THE INNER EAR
Dr(Prof) Rahul Kawatra(HOD)
Dr Mohd Shakeel (Guide)
Dr Satveer Singh J1

2. 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

3. DEVELOPMENT OF INNR EAR

4. LABYRINTH
• LABYRINTH or INNER EAR EAR
• Consists of two parts
• Bony labyrinth
• Membranous labyrinth

5. INNER EAR
The inner ear consists of a
membranous labyrinth
encased in an osseous labyrinth

6. 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

8. INNER EAR
• Cochlea
• Snail shaped bony structure
• Contains endolymph and perilymph
• Auditory fluids that aid in transmission of
sound vibrations

9. 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

10. EAR

11. PARTS OF INNER EAR

12. 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

13. THE COCHLEA
The 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

14. COCHLEA UNCOLILED

15. COCHLEA
Reissner membrane
and the basilar
membrane divide
the cochlea
longitudinally into
three scalae;
Scala media
Scala vestibuli
Scala tympani

16. SPIRAL ORGAN

17. 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

18. ORGAN OF CORTI
Scala media is more or
less triangular, formed by
the reissner’membrane,
basilar membrane and
the structures called
stria vascularis
The fluid that fills the
scala tympani and scala
vestibuli is called
perilymph and that
which fills the scala
media is called
endolymph
Organ of corti(spiral organ)
is provided with hair cells

19. 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

20. ORGAN OF CORTI
Two type of cells
Supporting cells such as
deiter’cells support hair
cells
Hair cells(receptor cells) :
that transduce sound
The tops of the hair
cells and pillar cells
form the reticular
membrane
The tectorial membrane is
loosely coupled to the
Reticular membrane
Organ of corti transduces
pressure waves to action
potential

21. 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

22. STEROCILIA
STERIOCILIA ON
INNER
AND OUTER HAIR
CELLS
ARE ARRANGED IN
A CURVED Or V
SHAPED
ROWS THAT FACE
TOWARD THE
MODIOLUS

23. FREQUENCY REPRESENTATION

24. CUT SECTION OF THE COCHLEA

25. COCHLEAR NERVE

26. HAIR CELLS
Afferent fibres (that go to the brain)
innervate the inner hair cells
Efferent fibres innervate the
outer hair cells
Inner hair cells are sensory cells
responsible for 95%
information to the brain
Outer hair cells are motor cells
that ampliphy the movements of
the basilar membrane in response
to a stimulus
Some of this energy is
transmitted back to middle ear
which can be recorded as
otoacoustic emission

27. CENTRAL AUDITORY
PATHWAY
Cochlear nerve from
cochlea to cochlear
nucleus in brain
stem
Auditory nerve splits
into two streams
red which go to the
ventral cochlear
nucleus
Green go to the
dorsal neucleus

28. CENTRAL AUDITORY
PATHWAY
From 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 lobe
Minute differences in
timing and loudness in each
ear is localised by dorsal
cochlear nucleus

29. 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

30. VESTIBULAR
SYSTEM
Three semicirular
ducts and otolith
organs
Three canals are at
right angles to each
other
Represent three axes
of rotation
Vertical
Anterioposterior
Trnsverse

31. SEMICIRCULAR CANALS
• Named according to their position
1 anterior or superior canal
2 Posterior canal
3 Lateral or horizontal or external canal
Anterior and posterior canal are vertical
Lateral canals of both sides are horizontal and in the
same plane at an angle of 30 degrees

32. 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

34. SEMICIRCULAR CANALS

35. AMPULLA
Two ends of canals
One enlarged
called ampulla and
it contains receptor
organs called crista
ampularis

36. 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

37. OTOLITH ORGAN OR VESTIBULE
• Utricle communicates with the
saccule through utricular saccular
duct
• Saccule communicates with
cochlea through ductus reunion
Endolymphatic 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

38. 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 proteoglycan
These cells are arranged in plane semilunatum(group of
epithelial cells) around hair cells

39. CRISTA AMPULARIS

40. HAIR CELLS
Hair cells are the
receptor cells of crista
ampularis
Two types of cells
Hair cells of
semicircular canal
Saccule and utricle
Receive both
Afferent and efferent
nerve terminals

41. HAIR CELLS
Type 1 hair cells flask
shaped
Afferent 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
shaped
Both afferent and efferent
terminate without
forming calyx on the cell
body

42. CUPULA
From 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

43. 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

44. MACULA
Blankets of calcium
Carbonate crystals are
On the top of
Gelatinous matrix
Surrounding hair
cells
The breakage of
these crystals results
in benign positional
Vertigo

45. BLOOD SUPPLY TO
VESTIBULAR END ORGANS
Anterior inferior
cerebellar artery
branch of basilar artery
Anterior 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

46. NERVE SUPPLY TO
VESTIBULAR APP
First order neurone
Bipolar in nature
Body or soma is in
the
Scarpa ganglion
Situated in internal
Auditory meatus

47. 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

48. 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

49. 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 tract
This tract is involved in reflex movements of head and body
during postural change
3 Vestibuloreticular tract
These fibres are concerned with facilitation of muscle tone
4 vestibulo – cerebellar tract
Involved in coordination of movement acc. To body
position

50. THANK YOU