Download 14anat2

Tympanic Membrane
1
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.
2
Tympanic Membrane
• Very thin and translucent (wax paper).
• Average thickness is 0.74 mm (.003 inches).
• Elliptically shaped
– Vertically .9 cm
– Horizontally .8 cm
3
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.
4
Tympanic Membrane
5
6
Middle Ear
•
•
•
•
Tympanic Cavity
Ossicles
Eustachian Tube
Middle Ear Muscles
7
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).
8
Tympanic Cavity
9
Tympanic Wall
10
Medial Wall
11
Posterior Wall
12
Aditus and Pyramidal Eminence
13
Anterior Wall
14
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.
15
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.
16
Ossicles
17
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).
18
Ossicular Chain
• Function
– Sound transmission to oval window
– Protect cochlea from intense vibrations by
changing axis of rotation of stapes.
19
Malleus
20
Incus
21
Stapes
22
Eustachian Tube
• Function
– Pressure equalization
– Drainage
• Description
– 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.
23
Eustachian Tube
24
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.
25
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
26
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.
27
Middle Ear Muscles
28
Tensor Tympani Muscle
29
Stapedius Muscle
30
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.
31
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.
32
Example of impedance mismatch
33
Areal Advantage
• 17:1 (55:3) areal advantage between
tympanic membrane and oval window and
yields
34
Lever Advantage
• 1.3:1 lever advantage
QuickTime™ and a
Animation decompressor
are needed to see this picture.
35
Resonance of the Middle Ear
• The middle ear
ear system creates
a gain of nearly 30
dB between 1000
and 2000 Hz.
36
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.
37
Summary
38