This document provides information about the anatomy and function of the inner ear. It describes the bony and membranous labyrinth that make up the inner ear's complex structure. Key components like the semicircular canals, cochlea, utricle, saccule and their roles in balance and hearing are explained. The basilar membrane, hair cells, and organ of Corti that are responsible for mechanotransduction and sound signal processing in the cochlea are discussed in detail. Common clinical conditions affecting the inner ear like BPPV, Meniere's disease, and labyrinthitis are also mentioned.

1. BY
Dr.K.AMRITHAANILKUMAR
PRESENTS

3. Kural 411
செல்வத்துட் செல்வஞ் செவிச்செல்வம் அச்செல்வம்
செல்வத்து செல்லாந் தலல.
TRANSLATION
Wealth of wealth is wealth acquired be ear attent;
Wealth mid all wealth supremely excellent.
EXPLANATION :
Wealth (gained) by the ear is wealth of
wealth; that wealth is
the chief of all wealth.

4. INNER EAR

5. Inner ear
• It exits within the temporal bone (
petrous bone )
• It is a complex structure . It is located
in a bony cavity called bony labyrinth
• It is filled with a fluid called perilymh ,
which is similar to CSF

6. Bony labryinth

7. Within the bony labyrinth is the
membranous labyrinth

8. Membraneous labyrinth
• Has 2 parts
• semicircular canal – 3 lateral ,
posterior & superior ( crista ampularis )
angular secretion
• utricle & saccule – utricle 5 opening of
semicircular canal ( macula ) linear
acceleration

9. cochlea
• central axis modiolus
• cochlear canal – runs 2 ½ turns
• cochlear duct - Scala vestibule , Scala
tympani , Scala media & organ of corti
openings – fenestra vestibule
& fenestra cochlea
hair cells ( inner & outer )
transduction of mechanical
energy to electrical energy

11. • cochlear canal - divided into Scala
vestibuli & Scala tympani by spiral
lamina & basilar membrane
cochlear duct is within
cochlear canal
receptor of organ hearing –
organ of corti
• organ of corti - specialized organ of
hearing
lies within cochlear duct
on the basilar membrane
contains hair cells –
impulses carried by VII nerve

13. • receptors for balancing – macula (
thickening – in the walls of saccule &
utricle )
crest ( in the
ampulla of semicircular ducts )

14. Basilar membrane
• Forms the floor of scala media
• 35mm long
• Auditory nerve endings are located
in BM
• Organ of corti resides on the BM

16. • Width
• Base ( 0.1 mm ) = narrow & stiff
• Apex (0.5 mm ) = boad / wide &
flaccid
• Opposite to cochlear ducts width
• Reacts more to vibrations of IE than
do most of the other structures.

17. Hair cells
• Hair cells lays down on the fibrous BM
• 3 – 5 rows of 12, 000 o 15, 000 parallel
outer hair cells (OHCs)
• One row of 3, 000 inner hair cells ( IHCs)
• On the top of each hair cells are hair –
like projection called “stereocilia”
• Stereo cilia on the top of OHCs are
embedded in the tectorial membrane

19. The direction in which stereo cilia are
bent during stimulation
• If cilia bend in one direction – nerve
cells are stimulated
• If cilia bend in the other way – nerve
impulses are inhabited
• If cilia bend to the side - no
stimulation at all

20. cochlear microphone
• Resemblance between cochlea &
microphone in their function
• cochlea convers sound waves into an
energy form useful to the auditory nerve
• microphone converts the sound pressure
coming form a speakers mouth into an
alternating electrical current
• This action is called cochlear
microphone (CM )

21. • a result of changes in polarization caused
by the bending back & forth of hair cells
cilia
• for every up & down cycle of BM , there is
an one in & out cycle of stereo cilia of the
OHCs causing them to become
alternatively depolarized & hyper
polarized
• CM can be measured by placing needle
electrode over the RW or within the
cochlea

23. Action potential
• A change in the electrical potential
occurring on the surface of each
neuron after they are being stimulated
by HCs
• Increases in the intensity of the
auditory input signal to the cochlea
result in increased electrical output
from HCs
• This stimulation causes increased
electrical activity in the neuron

24. Transformer action
• It is accomplished by
• Lever action of ossicles : handle of malleus is 13
times longer than long process of incus

25. Hydraulic action of
tympanic membrane
• the area of tympanic membrane is much
larger than the area of stapes footplate . the
average ration is 21:1 .
• the effective vibratory area of tympanic
membrane is only 2/3 rd. , so the effective
area ratio is reduced to 14: 1 .
• this is the mechanical advantage provided by
the tympanic membrane

26. Curved membrane effect
movements of the tympanic membrane
are more at the periphery than at the
centre

27. CLINICAL ANATOMY OF INNER
EAR
1. Benign paroxysmal positional vertigo (BPPV)
- also known
as positional vertigo
- It is a dizzy or spinning
sensation in your head
- most common type
of vertigo.

28. 2. Meniere's disease
causes episodes of vertigo, ringing
in the ears (tinnitus), ear
pressure/fullness and hearing loss.

29. 3. Labyrinthitis and vestibular
neuritis
- occurs when the
Hearing & balance
nerves become inflamed
- resulting in sudden
1. hearing loss
2. balance problems
3. vertigo.

30. 4. Superior semicircular canal dehiscence (SSCD)
- patient has a loss or absence
of the bone that covers
your superior
semicircular canal
Symptoms
1. pressure/
sound-induced vertigo
2. hearing loss
3. ear pressure,
4. hearing your
own breathing and blinking

31. REFERENCES
• Diseases of Ear, Nose and Throat & Head
and Neck Surgery by P L Dhingra
• BD Chaurasia's Human Anatomy Regional
and Applied Dissection and Clinical: Vol. 3:
Head-Neck Brain

32. A
Special
Thank you
To
A
Very
Special Doctor
en love da Homoeopathy