this ppt is about anatomy and physiology in brief mainly taken from standard test books and their is a mention of middle ear spaces in this ppt

1. ANATOMY AND PHYSIOLOGY OF
MIDDLE EAR

2. EMBRYOLOGY OF MIDDLE
EAR
PHARYNGEAL POUCH:-
PROXIMAL NARROW PART=EUSTACHIAN TUBE
DISTAL DILATED PART=
1.TYMPANIC CAVITY
2.ANTRUM
3. ATTIC
4.MASTOID AIR CELLS
OSSICLES=
1st ARCH CARTILAGE=1.HEAD OF MALLEUS
2.BODY OF INCUS
2nd ARCH CARTILAGE=1.HANDLE OF MALLEUS
2.LONG PROCESS OF INCUS
3.CRURA OF STAPES
OTIC CAPSULE=FOOT PLATE OF STAPES

3. Middle ear spaces
 Mucous membrane lines the bony walls
of tympanic cavity and it extends to
cover the ossicles and supporting
ligaments
 Mucosal folds separate middle ear
space in to compartments

4. Major mucosal folds
1. Superior malleolar
2. Lateral malleolar
3. Lateral incudal
4. Medial incudal
5. Superior incudal
6. Inter ossicular

5. COMPARTMENTS AND FOLDS OF
TYMPANIC CAVITY:
 attic compartment:
1. anterior compartment
2. posterior compartment
a) superior incudal space
b) medial incudal space
 compartment of mesotympanum
1.anterior malleolar fold
2.posterior malleolar fold

6. ISTHMUS TYMPANI ANTICUS:
 It lies between tensor tympani
fold and crura of stapes.
ISTMUS TYMPANI POSTICUS:
 Located near tip of short
process of incus between
posterior incudal ligament
,medial incudal fold , pyramid
and stapedius muscle

7. Anterior pouch of vontroltsch:
 Between anterior malleolar fold
and tympanic membrane
anterior to handle of malleus
Posterior pouch of vontroltsch:
 b/w post malleolar fold and T.M
posterior to handle of malleus

8. Spread of cholesteatoma
 Posterior epitympanic
cholesteatoma:
Orginates at prussack’s space –
lateral to ossicles – superior
incudal space – aditus and antrum
 Posterior mesotympanic
cholesteatoma :
Orginate at post-sup quadrant of
pars tensa – lies medial to
ossicles – spread to involve facial
recess and sinus tympani –
reaches mastoid via posterior
tympanic isthmus

9. Anterior epitympanic
cholesteatoma:
Orginate from epitympanic
retraction anterior to head of
malleus – reaches
mesotympanum via anterior
pouch of von troltsch –
involve supra tubal recess –
geniculate ganglion at risk

10. TYMPANIC CAVITY(MIDDLE
EAR):
DIVIDED IN TO 3 PARTS:
1. EPITYMPANUM (ATTIC)
2. MESOTYMPANUM
3. HYPOTYMPANUM

11. LATERAL WALL OF MIDDLE
EAR: FORMED BY
1.BONY LATERAL WALL OF
EPITYMPANUM
2.TYMPANIC MEMBRANE
3.BONY LATERAL WALL OF
HYPOTYMPANUM
 PETROTYMPANIC FISSURE:
RECIEVES:
1. ANTERIOR MALLEOLAR
LIGAMENT
2. ANTERIOR TYMPANIC BRANCH
OF MAXILLARY ARTEY
 CANAL OF HUGIER:MEDIAL
WALL OF PETROTYMPANIC
FISSURE THROUGH WHICH
CHORDA TYMPANI RUNS OUT
 COURSE OF CHORSA TYMPANI

12. ROOF OF THE MIDDLE EAR:
 TEGMEN TYMPANI: FORMED BY
PETROUS AND SQUAMOUS PORTION OF
TEMPORAL BONE
 PETOSQUAMOUS SUTURE:ROUTE OF
INFECTION IN TO EXTRA DURAL SPACE
IN CHILDREN

13. ANTERIOR WALL OF MIDDLE
EAR
lower 1/3rd:- plate of bone
covering carotid artery
middle 1/3rd:-
1.eustachian tube
2.canal for tensor tympani
upper 1/3rd:-has anterior
epitympanic sinus anterior to
ossicle heads&can hide
cholesteatoma in canal wall up
surgeries

14. POSTERIOR WALL:-
 aditus
 processus pyramidalis
 vertical portion of facial
nerve
 facial recess
(suprapyramidal recess)
 sinus tympani (infra
pyramidal recess)

15. FLOOR OF MIDDLE EAR:
 formed by :-pneumatised bone
 separates from jugular bulb
 tympanic branch of glossopharyngeal nerve
enters at junction between floor and medial
wall

16. MEDIAL WALL OF THE
MIDDLE EAR:
three depressions:
1. oval window
2. round window
3. sinus tympani
 facial nerve canal
 dome of the lateral
scc:-posterior and
lateral to facial canal

17. MUCOSA OF TYMPANIC
CAVITY:-
 mucous secreting resporatory ciliated epithelium
 ventilation route from mesotympanum and
epitympanum is via two small openings
1. anterior isthmus tympani
2. posterior isthmus tympani
prussak's space:- site for cholesteatoma
laterally=pars flaccida
medially = neck of malleus
inferiorly=lateral process of malleus
superiorly=lateral malleolar fold

18. COMPONENTS OF
TYMPANIC CAVITY:
EAR OSSICLES: malleus= head,neck,
anterior process,
lateral process ,handle
 incus=body,
short process,
long process,
lenticular process
 stapes=head,neck,
anterior crura,
posterior crura,foot plate
 long axis of stapes is
always horizontal

19. MUSCLES OF MIDDLE EAR:
1. tensor tympani
2. stapedius:-supplied by a
branch of mandibular
nerve
nerves:
1. chorda tympani
2. tympanic plexus

20. BLOOD SUPPLY OF
MIDDLE EAR:-
 from branches of :
1. middle meningeal artery
2. maxillary artery
3. ascending pharyngeal artery
4. stylomastoid branch of posterior
auricular artery
 nerve supply:-sensory:-ixth cranial nerve
through tympanic plexus
 motor:-
1. tensor tympani=mandibular division of vth nerve
2. stapedius=facial nerve

21. intensity
 Defined as the power transmitted by sound wave
through a unit area
 Intensity is dependent on pressure and velocity
 Intensity= peak pressure x peak velocity/2
 Displacement produced by sound wave vary with
frequency if intensity is constant
 Low frequency vibration produces greater
displacement

22.  Sound is alternate compression
and rarefraction of air
 2 properties of sound: intensity
and frequency

23. IMPEDANCE
Impedance is defined as resistance
offered by a medium for
transmission of sound

24. DECIBEL
 Measurement of sound level
 It is logarithmic unit of measurement that
express the magnitude of physical
quantity of sound ,relative to reference
level
 A difference of 1 db is the minimum
perceptive change in volume of sound

25. FUNCTIONS OF MIDDLE
EAR
25

26. MIDDLE EAR FUNCTIONS
 Couples sound energy to cochlea
 Provide physical protection for cochlea
 It serves as an acoustic transformer to match the
impedance of air to the much higher impedance
of the cochlear fluids
 It couple sound preferably to only one window of
the cochlea , thus producing differential pressure
between windows ,required for the movement of
cochlear fluids

27. MODE OF VIBRATING MIDDLE
EAR STRUCTURES
TYMPANIC MEMBRANE:
 It moved to and fro, it is buckled in the
regions between manubrium of malleus
and the , anterior and posterior edges.
 Inferior edges T.M – vibration greatest

28. in high frequencies
above 6kHz, the
pattern becomes
much more
complex, vibration
breaks up in to
many small zones
with the reduction in
efficiency of transfer
of vibration.

29.  The axis of rotation of
the ossicles and the
axis of suspension by
their ligaments
coincide with their
centre of rotational
inertia , so bones
vibrate with very little
loss through
suspending ligaments

30. Movement of stapes
 up to 1 kHz – stapes foot plate moves
primarily like a piston
 Higher frequencies : vibration become
more complex , with rotatory motion
along both the long and short axis of the
foot plate

31. IMPEDANCE TRANSFORMER
 middle ear acts as
impedance
transformer
 It transfers the
incoming vibrations
from large low
impedance T.M to
much smaller, higher
impedance ,oval
window.

32. Impedence transformer will change the
low pressure , high displacement
vibration of air into high pressure , low
displacement vibrations suitable for
driving the cochlear fluids

33. Impedence mismatch
IF THERE WAS NO MIDDLE EAR
SYSTEM ,99% OF SOUND WAVES
WOULD HAVE REFLECTED BACK
FROM OVAL WINDOW
MIDDLE EAR BY ITS IMPEDENCE
MATCHING PROPERTY ALLOWS
60% OF SOUND ENERGY TO
DISSIPATE IN INNER EAR
33

34. (a) HYDRAULIC ACTION OFTYMPANIC MEMBRANE
 Total effective area of tympanic
membrane 45mm2
 Area of stapes footplate is 3.2mm2
 Effective areal ratio is 14:1
 Thus by focusing sound pressure from
large area of tympanic membrane to
small area of oval window the
effectiveness of energy transfer
between air to fluid of cochlea is
increased
34

35. (b) Lever action of ossicles
Handle of malleus is 1.3 times
longer than long process of
incus
Overall this produces a lever
action that converts low
pressure with along lever
action at malleus handle to
high pressure with a short lever
action at tip of long process of
incus
35

36. (c) Action of tympanic
membrane
 Eustachian tube equilibrates the air
pressure in middle ear with that of
atmospheric pressure, thus
permitting tympanic membrane to
stay in its most neutral position.
 A buckling motion of tympanic
membrane result in an increased
force and decreased velocity to
produce a fourfold increase in
effectiveness of energy transfer
36

37. PHASE DIFFERENTIAL
EFFECT
 Sound waves striking the tympanic membrane
do not reach the oval and round window
simultaneously.
 There is preferential pathway to oval window
due to ossicular chain.
 This acoustic separation of windows is
achieved by intact tympanic membrane and a
cushion of air around round window
 This contributes 4dB when tympanic
membrane is intact
37

38. INFLUENCE OF MIDDLE EAR
MUSCLES
 2 muscles in the middle ear
1. Tensor tympani muscle
2. Stapedius muscle
Tensor tympani muscle :
Insertion : It inserts on to the top of manubrium
of malleus medially
Action : it pulls malleus medially and anteriorly ,
nearly at right angles to the normal
direction of vibration

39. STAPEDIUS MUSCLE:
Insertion : inserts on the posterior aspect of
stapes
Action : pulls stapes posteriorly
Muscles affect the transmission of sound in 2 ways
1. By increasing the stiffness of ossicular chain
2. By changing the direction of vibration of ossicles so
that movement is less effectively coupled to cochlea

40.  middle ear muscles contract in response to
sounds
 In humans only stapedius can be driven
acoustically , unless the sound is loud enough to
give a startle reflex
 To start a reflex, the stimuli be 80 db above
subject’s absolute threshold in the frequency
range from 250 kHz to 4 kHz

41. FUNCTION OF MIDDLE EAR
MUSCLE
1. Middle ear muscle reflex protects from noise
damage ,but the reflex is too slow to protect the
ear from sudden impulsive noise ,but have effect
on longer lasting noise
2. Reflex causes selective attenuation of low
frequency components in high intensity speech
thereby improving intelligibility of speech
3. Reflex reduces the influence of resonances in the
middle ear

42. Thank you