Transcript 14anat2

Tympanic Membrane
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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.
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Tympanic Membrane
• Very thin and translucent (wax paper).
• Average thickness is 0.74 mm (.003 inches).
• Elliptically shaped
– Vertically .9 cm
– Horizontally .8 cm
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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.
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Tympanic Membrane
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Middle Ear
•
•
•
•
Tympanic Cavity
Ossicles
Eustachian Tube
Middle Ear Muscles
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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).
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Tympanic Cavity
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Tympanic Wall
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Medial Wall
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Posterior Wall
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Aditus and Pyramidal Eminence
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Anterior Wall
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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.
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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.
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Ossicles
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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).
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Ossicular Chain
• Function
– Sound transmission to oval window
– Protect cochlea from intense vibrations by
changing axis of rotation of stapes.
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Malleus
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Incus
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Stapes
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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.
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Eustachian Tube
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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.
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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
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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.
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Middle Ear Muscles
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Tensor Tympani Muscle
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Stapedius Muscle
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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.
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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.
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Example of impedance mismatch
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Areal Advantage
• 17:1 (55:3) areal advantage between
tympanic membrane and oval window and
yields
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Lever Advantage
• 1.3:1 lever advantage
QuickTime™ and a
Animation decompressor
are needed to see this picture.
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Resonance of the Middle Ear
• The middle ear
ear system creates
a gain of nearly 30
dB between 1000
and 2000 Hz.
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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.
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Summary
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