The tympanic membrane (eardrum) collects sound waves in the air and transmits them to the middle ear. It is cone-shaped and angled at 55 degrees to maximize surface area within the ear canal. Composed of three tissue layers, it separates the outer and middle ear and attaches superiorly to the malleus bone. Vibrations of the malleus, incus, and stapes bones (the ossicles) amplify and transform sounds entering the inner ear. Two muscles in the middle ear, the stapedius and tensor tympani, protect hearing from loud sounds.

1. The tympanic membrane is the
receiver and collector of acoustic
pressure directed against the ear by
vibratory energy in the air around us.

2. The tympanic membrane (TM) is
conical, pointing medialward so that
more surface area of the membrane
can be available without having a
larger opening for a ear canal.

3. The TM is found to be at
approximately a fifty-five degree
angle (not perpendicular to the ear
canal) and has generally an elliptical
shape.

4. The tympanic membrane
(TM)/eardrum
 Is composed of three layers of
tissue.
 Separates the external ear from the
middle ear.
 Is connected to the malleus and
reflects the “cone-of-light”.

5. The three layers of tissue of the TM are:
1. The cutaneous layer (same layer as
the EAM)
2. The fibrous layer (the “compliance”
layer)
3. The mucous layer (same as the inner
liner of the middle ear cavity)

6. The TM attachment at its superior
portion to the malleus creates a
movement which would more
resemble a swinging motion than a
piston (in and out) motion.

7. One tenth of one decibel of sound
pressure will create movement of a
healthy tympanic membrane by as
little as 1/100 the thickness of a
hydrogen molecule—it is very
sensitive to sound pressure—yes
even barometric pressure.

8. The TM moves much more easily at
its inferior portion.
Note: Due to gravity, this is the area
which may become most easily
compromised by ear canal debris or
middle ear fluid.

9. When the TM becomes too flaccid
(floppy) or too tense, the sound
transfer to the middle ear bones
(ossicles) becomes easily influenced.

10. The three middle ear bones (ossicles)
are:
1. The malleus (attached to the TM)
2. The incus (attached to the
malleus and stapes)
3. The stapes (attached to the oval
window)

11. Two muscles are attached to the
middle ear bones.
1. A tendon attaches the stapedius
muscle to the stapes. (innervated
by the VII cranial/facial nerve)
2. A tendon attaches the tensor
tympani muscle to the malleus.
(innervated by the V cranial
nerve)

12. The movement of the three middle
ear bones creates a “mechanical
amplifier”.
It is also found to be an impedance
transformer changing low-
impedance sound waves into a high
impedance match with the inner ear
fluid.

13. As the movement of the malleus and
incus bones represent the to-and-fro
motion of a swing, they actually rock
the stapes in and out of the oval
window (do not push it in and out
like a plunger or piston).

14. This rocking action of the stapes
actually decreases once the brain
senses sound pressures greater than
seventy decibels due to the
contraction of the middle ear
muscles.

15. The most widely accepted theory
regarding this middle ear muscle
contraction is to protect the ear from
too much sound pressure—mostly
from low frequency energy (below
2000hz). In other words, their
contraction creates a high-pass filter.

16. The Eustachian tube
It equalizes the air pressure
between the middle ear cavity and
the external auditory meatus. It
usually opens and closes every time
we swallow.

17. The Eustachian Tube
It also serves as a drainage conduit
when any fluid has collected within
the middle ear such as the effects of a
head cold.