Transcript Anatomy and physiology of the middle ear

Lecture 4
Anatomy and physiology of the ME
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Anatomy and physiology of the ME
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Adult ME is almost oval, air filled space of
roughly 2 cm3
The roof of the middle ear is a thin layer of
bone, separating the middle ear cavity from
the brain
Upper portion - epitympanic recess or
epitympanum or attic
◦ Communicates with mastoid antrum (cavity)
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Below the floor of the ME is the jugular bulb
Narrowest at umbo
Behind the anterior wall is the carotid artery
The labyrinth of the inner ear lies behind the
medial wall
The mastoid process beyond the posterior
wall
The lateral portion of the ME is sometimes
called the membranous wall because it
contains the TM
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the middle ear is connected to the
nasopharynx, area where the back of the
throat and nose communicate via the
Eustachian tube
The Eustachian tube (ET) and the middle ear
form the middle ear cleft (space made of the
up from the ME and ET
The entire middle ear cleft together with the
TM is lined with mucous membrane
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Bone that surround the ear
It is honeycombed with hundreds of air cells
Each cell is lined with mucous membrane
These cells form the pneumatic mastoid of
the temporal bone
ME opens up, back, and outward in an area
called aditus ad antrum to communicate with
the mastoid\the protuberance behind the
auricle is called the mastoid process
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Promontory: a section of the bony portion of
the inner ear that extends to the ME, caused
by the basal turn on the cochlea
Oval window: above the promontory, filled by
a membrane that supports the base of the
stapes
Round window: below the promontory,
covered by a very thin, but tough elastic
membrane
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The middle ear contains three tiny bones
known as the ossicles: malleus, incus,
and stapes. The ossicles were given their
Latin names for their distinctive shapes; they
are also referred to as the hammer
‫مطرقة‬, anvil ‫ سندان‬, and stirrup ‫ركاب‬, respectively.
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The ossicles (also called auditory ossicles) are
three bones in either middle ear that are among
the smallest bones in the human body.
They serve to transmit sounds from the air to the
fluid-filled labyrinth (cochlea).
The absence of the auditory ossicles would
constitute a moderate-to-severe hearing loss.
The term "ossicle" literally means "tiny bone" and,
though the term may refer to any small bone
throughout the body, it typically refers to the
malleus, the incus and the stapes of the middle
ear.
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Malleus
◦ Manubrium, neck, head
◦ Short anterior and lateral processes near top of
manubrium
◦ Firmly attached to TM (along manubrium, lateral
process)
◦ The head of the malleus is connected to the incus
◦ This area of connection extends upward to the
aditus ad antrum
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Incus
◦ Body, long and short processes
◦ Long process (parallel to manubrium) bends into
lenticular process
◦ The end of the lenticular process sits squarely on
the head of the stapes
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Stapes
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Head, neck, twocrurae, footplate
Incudo-stapedial joint
Attached to oval window – annular ligament
The posterior crus is longer and thinner than the
anterior crus to aid in rocking motion
◦ The base, footplate occupies the space in the oval
window
◦ The stapes is the smallest and lightest named bone
in the human body
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The malleus and the incus are rigidly
connected
Inward and outward movement of the umbo
of the TM cause these bones to rotate, and
transfer this force to the stapes, which result
in the inward and outward motion of the oval
window
Ligament connection hold each ossicle in
place that their collective function in not
altered by gravity, when the head changes
position
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The ossicular chain is 2 to 6 mm in length,
and acts as a single unit when transmitting
the sounds above 800 Hz
The action of these ossicles provide energy
transformation
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Also called auditory tube
The ET is lined with __________ membrane
Much of this membrane is ciliated, the top
most cells contain cilia.
The movement of the cilia helps cleanse the
ME by moving particles down and out of the
ET
The ET enters the ME at 30° angle and passes
through the nasopharynx
The tube Is kept closed due to the spring
mechanism of the cartilage (adults)
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In adult humans the Eustachian tube is
approximately 35 mm (1.4 in) long
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A portion of the tube (1/3) proximal to the
middle ear is made of bone; this bony part is
about 12 mm in length.
The cartilage of pharyngotympanic tube,
about 24 mm in length.
◦ Normally closed
◦ Opens by reflex action of tensor veli palatini
 Swallowing, yawning, sneezing
 Innervated by trigeminal (N V)
 Thought to work with action of tensor tympani
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Orifice (opening) of the ET into the
nasopharynx tends to remain open until the
age of 6 months
The ET in infants is shorter, wider in relation
to its length and in more horizontal plane
than is in adults
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To equalise the pressure on both sides of the
TM to minimise its mobility
Some people experience fullness when
changing elevation (flying)
During ascension this fullness results when
the air in the EAC becomes rarified (thin),
while the ME remains at ground level
pressure, the sensation of fullness occurs
when the TM is pushed outward from greater
pressure from within the ME
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While decent the pressure in the middle ear
maybe less than the external ear so that the
TM is pushed in
The solution is to yawn, swallow or open the
ET to equalise the pressure
At extreme pressure changes the ET will lock
shut, making pressure equalising impossible
and great pain, it is likely for the TM to
rupture
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