human's inner ear ,which is third part of ear, Having cochlea and vestibular system.in this slide we will discuss about the anatomy and physiology of inner ear.

1. Anatomy & Physiology
of Inner ear
Ashutosh singh Mr. Ajay Mishra
Presenter: Guide:

2. EAR
• 1.Outer Ear 2.Middle Ear 3.Inner Ear

3. EAR
• 1.Outer Ear 2.Middle Ear 3.Inner Ear

4. INNER EAR
The Inner ear consist of dual-function mechanism for
serving the special sensory modalities audition and
equilibrium.
It is also known as Labyrinth.
It is situated in the temporal bone.

5. It has two parts
1.Cochlea :organ of hearing
2. Vestibular system: organ of equilibrium

6. Cochlea
 The outer duct is made up of bone & hence called as BONY LABYRINTH.
 The inside duct is made up of membranous materials and hence is called the
MEMBRANOUS LABYRINTH .

7. It is situated in the petrous part of temporal bone
It is snail like structure and coils in 2 and5/8 turns
around a bone called the modiolus.
The length of the cochlea is approx 35mm.
Around the modiolus in the cochlea the thread like bone
is osseous spiral lamina

8.  The two outer ducts i.e scala vestibuli & scala tympani meet
at the far end of the tube at an opening called as
HELICOTREMA.
 The stapes at the oval window is at the base of scala
vestibuli,& round window is at the basal end of the scala
tympani.
The cochlea is made up of 3 cavities
a.Scala vestibuli
b.Scale media
c.Scale tympani
Cross Section of Cochlea

9. Fluid
 Scala vestibuli & Scala tympani contains
perilymphatic fluid or perilymph.
 Scala media contains endolymphatic fluid or
endolymph

10. Composition of inner ear fluids
• Endolymph Perilymph
• Sodium(mEq/L) 5 140
• Potassium(mEq/L) 144 10
• Protein(mg/dL) 126 200-400
• Glucose(mg/dL) 10-40 85

11. Endolymph vs. perilymph
Endolymph Perilymph
Present in scala media.
Present in scala vestibuli, scala
tympani & spaces within OOC
High concen. K+ ions & low concen. Of
Na+
High concen. Na+ and Ca++ ions &
low concen. Of K+
Production of Endolymph directly
involves stria vascularis
Production of perilymph –
It is a filtrate of blood serum, which
is produced by the capillaries in the
spiral ligament
Perilymph is nothing more than CSF

12. The scala media is separated from the scala vestibuli above it by REISSNER’S
MEBRANE
And from the scala tympani below it by the BASILAR MEMBRANE.

Cut the cochlea

13. STRUCTURES INSIDE SCALA MEDIA/COCHLEAR
DUCT

14. o Outer wall of the cochlear duct
is covered with a band of
connective tissue called SPIRAL
LIGAMENT
o The top of the OSL is covered
by a thickened band of
periosteum called the LIMBUS.
o The BM is a fibrous membrane
that runs horizontally from the
OSL to the spiral ligament.
o Ressiner’s membrane is a thin
membrane that goes from the
top of the medial aspect of the
limbus to the spiral at an
upward angle of about 45.

15.  The rounded space formed by
the concave lateral side of the
limbus is called internal spiral
sulcus.
 Organ of corti, a sensory
organ of hearing sits on the
BM lateral to the internal
spiral sulcus.
 Tectorial Membrane arises
from the upper lip of limbus,
& forms the overlying
membrane of OOC.
 It is made up of collagen
fibers that gives it
considerable tensile strength
& make it quite compliant
(Zwislocki et al 1988).

16. Organ of corti
OOC is the sense organ of hearing and is situated on the basilar
membrane.
OOC is a complex arrangement of sensory hair cells along with the
various accessory cells & structure.
Important componant of the OOC are—
- Tunnel of Corti
- Hair cells
- Supporting cells
- Tectorial Membrane

19. Main features of ooc
 Upside down y- tunnel of corti
 Pillar or rods of corti
 Medial to tunnel- IHC’s
 Lateral- OHC’s
 Stereocilia
 Cuticular plate (thickening on the top of the hair cell)
 Reticular lamina ( impervious layer formed by the tops (Cuticular
plates) of the hair cells, as well s by the upper ends of the tunnel
cells & other supporting cells.

20. OHCs VS IHCs

21. OHCs IHCs
12000 3500
Tube like Flask shaped
Stereocilia of the OHCs are
firmly attached to the TECT M
The stereocilia of the IHCs are
not attached to the TM.
3 rows Single row
Only 5 % of afferent neuron
innervate OHCs
95% of afferent neuron
innervate IHCs
Each neuron is connected to
more than 10 OHCs
Each IHCs is connected to
more than 10 neurons
Most of the efferent neuron go
to OHCs
Few of the efferent neuron go
to IHCs

22. Cont….
OHCs IHCs
They are located away from the
modiolus
They are located closest to the
modiolus
The number of stereocilia vary
from 20 to 100 per cell from the
first and second rows in the base
(most) to the third row in the apex
(least)
On each hair cell, the stereocilia,
numbering about 60 per cell.

24. Physiology of Cochlea

25. • When the footplate of the stapes strikes the oval window having
mechanical energy, then oval window change mechanical energy into
chemical energy.
• And 99.99 % of the sound wave reflect back , and only .1% of the sound
wave transmit due to impedance.
• When oval window is receiving wave of Compression, then the round
window is at the phase of Rarefaction.

26. • Movement of the stapes footplate, transmitted to the cochlear fluid ,
move the basilar membrane and set up shearing force b/w the
Tectorial membrane and the hair cells.

28. Vestibular system
• 1.Vestibule 2.Semicircular canals
Organ of equilibrium (balance)

29. Vestibule
• Vestibule forms central position of bony labyrinth.
• It continuous with semicircular canals & the cochlea.
• Ovaid in shape(egg shape).
• Length -5mm (approx)
• Diameter -3mm (approx)
• Lateral surface –oval window

30. Cont.
• The membranous labyrinth in the vestibule consist of two sacs called
the utricle and saccule.

31. Utricle
• The utricle senses motion in the horizontal acceleration (eg, forward-
backward movement, left-right movement, or a combination
thereof).

32. Saccule
• The saccule senses motions in the sagittal (verticle) acceleration
(eg, up-down movement).

33. • The utricle and saccule are both largely
composed of macula tissue
• The stereocilia of the hair cells extend
into a viscous gel called the otolithic
membrane
• The macula is composed of hair cells
surrounded by support cells.
• On top of the otolithic membrane is a
layer of calcium carbonate crystals,
called otoliths.

34. 3 Semicircular Canals
1. Superior S.S.C. (15-20mm)
2. Posterior S.S.C (18-22mm)
3. Lateral (horizontal) S.S.C. (12-15mm)
• It lies posterior superior to the
• vestibule.
• All lies in different planes ,
• perpendicular to one another.
• Two canals form nearly right angle
length
The 3 semicircular canals are small, ringlike structures
Respond to rotational movement.

35. • Ampulla is the region where all canals meet into vestibule.
• The semicircular duct is in inside the canals having the endolymph .

36. • Place theory or resonance theory
• Traveling wave theory
• Telephone theory
• Standing wave theory
• Pressure patern theory
• Volley theory
• Frequency analytic theory
Theories of hearing

37. Resonance Theory
• This theory is proposed by Helmholtz(1857).
• According to this theory the basilar membrane
was constructed of segment that resonated in
response to different frequencies,and that
these segment were arranged according to
place along the length of the basilar
membrane

38. Traveling wave
• This theory is proposed by
Bekesy in 1960
• According to this theory– The
traveling wave is the
mechanism that translates
signal frequencies into place
of stimulation alon the
basilar membrane
• High frequencies are
represented toward the base
of the cochlea, and lower at
the apex.

39. Reference:
Essential of audiology Gelfand
Speech and hearing science Willard R. Zemlin
Anatomy and physiology in
health and illness Ross & Wilson
Neuroscience Bhatnagar
Diseases of E.N.T. P.L. Dhingra

40. Thank You