1. Middle ear

3. Middle ear structures Middle ear cavity/tympanum Tympanic membrane
Ossicles/Middle ear bones

4. 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

5. Tympanic cavity Similar to a box with six surfaces
Lateral wall or membraneous wall: Formed by TM and squamous portion of TB.
Medial wall or labyrinthine wall: Promontory (outer wall of inner ear)
(oval and round windows, prominence of facial nerve)
Anterior wall or carotid wall (opening of ET and tendon of tensor tympani)
Posterior wall or mastoid wall (tympanic aditus, fossa incudis, pyramidal prominence, facial nerve through tympanic sulcus)
Inferior wall or jugular wall (tympanic plate of TB)
Superior wall or tegmental wall (tegmen tympani, continuing posteriorly to tympanic atrium)

6. 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

7. 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:
Radiates outward from center
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

8. Tympanic membrane, cont’d.
Umbo: Region of maximum concavity
Position changes as EAM lengthens after birth
Important landmarks visible
Tympanic membrane attached to ossicles.

9. Ossicles Malleus: Hammer Incus: Anvil
Stapes: Stirrup
Head of malleus and body of incus located in the epitympanic recess

11. Malleus 9 mm long, 23-37 mg weight Head with articular facet Neck
Anterior and lateral processes
Handle or Manubrium

12. 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)

13. Stapes
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 piston-like, movement of stapes.

15. 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

16. Ossicular connections, cont’d.
Suspended in the middle ear cavity by axial ligaments and muscle tendons
Middle ear muscles
Tensor tympani and stapedius

17. 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

18. 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