Middle ear
Middle ear structures

Middle ear
cavity/tympanum

Tympanic
membrane

Ossicles/Middle
ear bones
Middle ear cavity

2-4 mm horizontal, 13 mm
vertical, approximately 2 cm3 in
volume

Comprised of

Tympanic cavity between
outer and inner ear

Epitympanic recess above
the TM

Mastoid recess contained in
the mastoid region of the
temporal bone
Tympanic cavity
Similar to a box with six surfaces
1.
Lateral wall or membraneous wall:
2.
Medial wall or labyrinthine wall:
Formed by TM and squamous portion of
TB.
Promontory (outer wall of inner ear)
(oval and round windows, prominence of
facial nerve)
3.
Anterior wall or carotid wall (opening of
ET and tendon of tensor tympani)
4.
Posterior wall or mastoid wall (tympanic
aditus, fossa incudis, pyramidal
prominence, facial nerve through
tympanic sulcus)
5.
Inferior wall or jugular wall (tympanic
plate of TB)
6.
Superior wall or tegmental wall (tegmen
tympani, continuing posteriorly to
tympanic atrium)
Tympanic membrane

Oval shaped lateral surface

Thick periphery called annulus with the notch of Rivinus

Located in a bony groove called tympanic sulcus

8-9 horizontal, 9-10 mm vertical axis, 0.1 mm thick.

Held in place by fibers and cartilage

Cone shaped, translucent

55 to 90 mm2 in area
http://www.ghorayeb.com/AuricleEACAnatomy2.html
Three layers
Outer: Epidermis of EAM
Inner: Mucosal lining of middle ear
space
Middle: Collagen fibers, support for
TM.
Middle layer composed of two sets of
fibers:
1.
Radiates outward from center
2.
Concentric rings of fibers

Two regions in tympanic
membrane:

Superior region: Pars
flaccida (defined by anterior
and posterior malleolar
folds and malleolar
prominence)

Inferior region: Pars tensa
Tympanic membrane, cont’d.

Umbo: Region of maximum concavity

Position changes as EAM lengthens after birth

Important landmarks visible

Tympanic membrane attached to ossicles.
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.html
Ossicles
1.
Malleus: Hammer
2.
Incus: Anvil
3.
Stapes: Stirrup

Head of malleus and body of incus located in the
epitympanic recess

http://oto.wustl.edu/bbears/ossicle.htm
http://www.ghorayeb.com/StapesPics.html
http://audilab.bmed.mcgill.ca/~daren/3Dear/mid1.html
Malleus

9 mm long, 23-37 mg
weight

Head with articular facet

Neck

Anterior and lateral
processes

Handle or Manubrium
Incus

About 23-32 mg weight

Body

Short crus/process in
epitympanic recess,
around 5 mm

Long crus/process with
lenticular process,
around 7 mm
(Plural of crus: Crura)

2-5 to 3.8 mm tall, 2.1 to 4.3
mg weight. Footplate area
around 3.2 mm2

Head, with spine for
attachment of stapedial
tendon

Neck

Two bony crura, anterior and
posterior

Flat oval bone called footplate

Medial surface of footplate
fastened to wall of oval
window by annular ligament.

Unique connection allows for
rocking, rather than pistonlike, movement of stapes.
Stapes
Ossicular connections

Malleus: Manubrium of malleus
connects to umbo of TM.

Incus: Head of malleus connects
to body of incus (incudo-mallear
joint)

Stapes: Inferior process of incus
connects to form lenticular
process, which connects to the
stapes (incudo-stapedial joint)

Footplate of the stapes
connects to the oval window
Ossicular connections, cont’d.

Suspended in the
middle ear cavity by
axial ligaments and
muscle tendons

Middle ear muscles

Tensor tympani and
stapedius
Tensor tympani

Enters middle ear through anterior wall of tympanum.

Connected to manubrium/neck of the malleus

Activated by the trigeminal nerve

Muscle runs parallel and superior to osseous foundation of the
ET, separated by septum canalis musculotubarii)

Pulls malleus in anterior and posterior direction
Stapedius muscle
•Tendon enters the middle ear
space through opening in the
posterior wall of the tympanum
(pyramidal eminence)
•Attached to the head of the
stapes
•Activated by the facial nerve
•Pulls stapes in the posterior
direction