1. Tympanic Membrane

2. Tympanic Membrane infant adult
EAM terminates at the tympanic membrane TM.
In newborns the TM is horizontal
In adults , the TM sits at a 55 degree angle.
Ossification of EAM causes changes in angle of TM until about age 5 when it reaches adult position.

3. Tympanic Membrane Very thin and translucent (wax paper).
Average thickness is 0.74 mm (.003 inches).
Elliptically shaped
Vertically .9 cm
Horizontally .8 cm

4. Tympanic Membrane Three Layers of TM
Ectoderm (cutaneous) - continuous with EAM
Mesoderm (fibrous)
Radial Fibers
Concentric Fibers
Endoderm (mucous) - continuous with Tympanic Cavity.
Pars Tensa contains all three layers.
Pars Flacida DOES NOT contain fibrous layer.

5. Tympanic Membrane

7. Middle Ear
Tympanic Cavity
Ossicles
Eustachian Tube
Middle Ear Muscles

8. Tympanic Cavity About same size/shape as an aspirin tablet.
15 mm (superior to inferior)
15 mm (anterior to posterior)
5 mm (lateral to medial)
For descriptive purposes the TC has been compared to a six-sided room (4 walls + ceiling + floor).

9. Tympanic Cavity

10. Tympanic Wall

11. Medial Wall

12. Posterior Wall

13. Aditus and Pyramidal Eminence

14. Anterior Wall

15. Tegmen Also known as the superior wall. Paper thin.
Separates the tympanic cavity from the posterior cranial fossa which houses the temporal lobe.
Inflamatory conditions of middle ear can pass through the petrous-squamosal suture in children directly to the meninges of temporal lobe of cortex.

16. Jugular Wall No landmarks.
Jugular vein is found inferior to this wall.
Glomus bodies can push up through this wall from jugular vein causing glomus jugularis.

17. Ossicles

18. Ossicles Connects tympanic membrane with the oval window.
Smallest bones in the human body
Connected via a series of joints.
Held in place by a series of ligaments, tendons, and joints (see p. 455 of Zemlin).

19. Ossicular Chain Function Sound transmission to oval window
Protect cochlea from intense vibrations by changing axis of rotation of stapes.

20. Malleus

21. Incus

22. Stapes

23. Eustachian Tube Function Description Pressure equalization Drainage
35 mm and drops at about a 40 degree angle.
Cartilaginous portion is 2/3, osseous portion is 1/3
Osseous portion is open, Cartilaginous portion is usually closed.
Begins at tympanic cavity and terminates in nasopharynx.

24. Eustachian Tube

25. Eustachian Tube Function
Tensor palatini definitely involved in opening ET.
Levator palatini role is not clear.
Opening has been described as a milking action and also been described as the tensor palatini pulling on side of ET, opening the tube.

26. Eustachian Tube Differences between adults and infants Angle of ET
Adults - about 40 degrees
Children - more horizontal
Length
Adults - about 35 mm
Children - shorter
Flaccidity
More flaccid in children

27. Eustachian Tube Cleft Palate
Normally fibers from tensor palatini and levator palatini insert into the velum.
In cleft palate fibers from these two muscles insert into the levator palatini may insert into hard palate and tensor palatini may insert into lateral portions of velum.
Number of fibers for these two muscles is often reduced in people with cleft palate.

28. Middle Ear Muscles

29. Tensor Tympani Muscle

30. Stapedius Muscle

31. Function of the middle ear
The middle ear system that includes the tympanic membrane and the ossicles, acts as an impedance matching device between the air-borne sound waves and the fluids of the inner ear.

32. Function of the middle ear
Must consider tympanic membrane
Impedance … opposition to the flow of energy.
Impedance mismatch… occurs when you have two mediums of differing impedances.
Impedance mismatch occurs between gas (air) in environment and fluid of inner ear.

33. Example of impedance mismatch

34. Areal Advantage
17:1 (55:3) areal advantage between tympanic membrane and oval window and yields

35. Lever Advantage
1.3:1 lever advantage

36. Resonance of the Middle Ear
The middle ear ear system creates a gain of nearly 30 dB between 1000 and 2000 Hz.

37. Resonance of the Middle Ear
Effects of increased mass and stiffness.
increase in mass causes downward shift of resonant frequency.
increase in stiffness causes upward shift in resonant frequency.

38. Summary