1. Becoming Familiar with the Middle EarBecoming Familiar with the Middle Ear
 The tympanic membrane (TM)/eardrumThe tympanic membrane (TM)/eardrum
1.1. Is composed of three layers of tissue.Is composed of three layers of tissue.
2.2. Separates the external ear from theSeparates the external ear from the
middle ear.middle ear.
3.3. Is connected to the malleus andIs connected to the malleus and
reflects the “cone-of-light”.reflects the “cone-of-light”.

2. Becoming Familiar with the Middle EarBecoming Familiar with the Middle Ear
The three layers of tissue of the TM are:The three layers of tissue of the TM are:
1.1. The cutaneous layerThe cutaneous layer (same layer as the EAM)(same layer as the EAM)
2.2. The fibrous layerThe fibrous layer (the “compliance” layer)(the “compliance” layer)
3.3. The mucous layerThe mucous layer (same as the inner liner of the(same as the inner liner of the
middle ear cavity)middle ear cavity)

3. Becoming Familiar with the Middle EarBecoming Familiar with the Middle Ear
 The three middle ear bones are:The three middle ear bones are:
1.1. The malleusThe malleus (attached to the TM)(attached to the TM)
2.2. The incusThe incus (attached to the malleus and stapes)(attached to the malleus and stapes)
3.3. The stapesThe stapes (attached to the oval window)(attached to the oval window)

4. Becoming Familiar with the Middle EarBecoming Familiar with the Middle Ear
 Two muscles attached to middle ear bones.Two muscles attached to middle ear bones.
 A tendon attaches theA tendon attaches the stapedius musclestapedius muscle to theto the
stapes.stapes. (innervated by the VII cranial/facial nerve)(innervated by the VII cranial/facial nerve)
 A tendon attaches theA tendon attaches the tensor tympani muscletensor tympani muscle
to the malleus.to the malleus. (innervated by the V cranial nerve)(innervated by the V cranial nerve)

5. Becoming Familiar with the Middle EarBecoming Familiar with the Middle Ear
The movement of the three middle earThe movement of the three middle ear
bones creates a “mechanical amplifier”.bones creates a “mechanical amplifier”.

6. Becoming Familiar with the Middle EarBecoming Familiar with the Middle Ear
 The Eustachian tubeThe Eustachian tube
It equalizes the air pressure between theIt equalizes the air pressure between the
middle ear cavity and the external auditorymiddle ear cavity and the external auditory
meatus. Usually opens and closes everymeatus. Usually opens and closes every
time we swallow.time we swallow.

7. Becoming Familiar with the Middle EarBecoming Familiar with the Middle Ear
 The areal ratioThe areal ratio
The eardrum (TM) has a surface area 17The eardrum (TM) has a surface area 17
times larger than the footplate of thetimes larger than the footplate of the
stapes (the footplate is attached to thestapes (the footplate is attached to the
oval window). An areal ratio can beoval window). An areal ratio can be
calculated based upon the difference incalculated based upon the difference in
size between the two surface areas.size between the two surface areas.

8. Becoming Familiar with the Middle EarBecoming Familiar with the Middle Ear
 Impedance transformerImpedance transformer
The low impedance of the air mediumThe low impedance of the air medium
moving the eardrum is defeated by themoving the eardrum is defeated by the
high impedance of the inner ear fluids.high impedance of the inner ear fluids.
This impedance mismatch is overcome byThis impedance mismatch is overcome by
the mechanical movement/energy of thethe mechanical movement/energy of the
middle ear bones.middle ear bones.

9. Becoming Familiar with the Middle EarBecoming Familiar with the Middle Ear
This mechanical amplifier coupled withThis mechanical amplifier coupled with
the areal ratio difference between thethe areal ratio difference between the
eardrum and the oval window create theeardrum and the oval window create the
middle ear transformermiddle ear transformer..

10. Becoming Familiar with the Middle EarBecoming Familiar with the Middle Ear
 Transduced energy/Middle ear transformerTransduced energy/Middle ear transformer
The acoustic sound information presented to theThe acoustic sound information presented to the
eardrum is transduced from sound wave energyeardrum is transduced from sound wave energy
through an air medium into mechanical energy.through an air medium into mechanical energy.
This coupled with the areal ratio complete theThis coupled with the areal ratio complete the
transformation of sound energy into the hightransformation of sound energy into the high
impedance of the inner ear fluids. Theimpedance of the inner ear fluids. The
movement of the middle ear bones creates themovement of the middle ear bones creates the
impedance matching function. This transformerimpedance matching function. This transformer
results in approximately 33 decibels of gain.results in approximately 33 decibels of gain.

11. Becoming Familiar with the Middle EarBecoming Familiar with the Middle Ear
For more specific information regardingFor more specific information regarding
the function of the middle ear muscles andthe function of the middle ear muscles and
biologic frequency modification, pleasebiologic frequency modification, please
refer to Lass & Woodford page 67.refer to Lass & Woodford page 67.