Middle ear Middle ear

Middle ear structuresMiddle ear structures

Middle ear Middle ear cavity/tympanucavity/tympanumm

Tympanic Tympanic membranemembrane

Ossicles/Middle Ossicles/Middle ear bonesear bones

Middle ear cavityMiddle ear cavity

2-4 mm horizontal, 13 mm 2-4 mm horizontal, 13 mm vertical, approximately 2 vertical, approximately 2 cmcm3 3 in volumein volume

Comprised ofComprised of

Tympanic cavity between Tympanic cavity between outer and inner earouter and inner ear

Epitympanic recess Epitympanic recess above the TMabove the TM

Mastoid recess contained Mastoid recess contained in the mastoid region of in the mastoid region of the temporal bonethe temporal bone

Tympanic cavityTympanic cavity

Similar to a box with six surfacesSimilar to a box with six surfaces

1.1. LateralLateral wall or membraneous wall: wall or membraneous wall: Formed by TM and squamous Formed by TM and squamous portion of TB.portion of TB.

2.2. MedialMedial wall or labyrinthine wall: wall or labyrinthine wall: Promontory (outer wall of inner ear)Promontory (outer wall of inner ear)

(oval and round windows, (oval and round windows, prominence of facial nerve)prominence of facial nerve)

3.3. Anterior wall or carotid wall (opening Anterior wall or carotid wall (opening of ET and tendon of tensor tympani)of ET and tendon of tensor tympani)

4.4. Posterior wall or mastoid wall Posterior wall or mastoid wall (tympanic aditus, fossa incudis, (tympanic aditus, fossa incudis, pyramidal prominence, facial nerve pyramidal prominence, facial nerve through tympanic sulcus)through tympanic sulcus)

5.5. Inferior wall or jugular wall Inferior wall or jugular wall (tympanic plate of TB)(tympanic plate of TB)

6.6. Superior wall or tegmental wall Superior wall or tegmental wall (tegmen tympani, continuing (tegmen tympani, continuing posteriorly to tympanic atrium)posteriorly to tympanic atrium)

Tympanic membraneTympanic membrane

Oval shaped lateral surfaceOval shaped lateral surface

Thick periphery called annulus Thick periphery called annulus with the notch of Rivinuswith the notch of Rivinus

Located in a bony groove Located in a bony groove called tympanic sulcuscalled tympanic sulcus

8-9 horizontal, 9-10 mm 8-9 horizontal, 9-10 mm vertical axis, 0.1 mm thick.vertical axis, 0.1 mm thick.

Held in place by fibers and Held in place by fibers and cartilagecartilage

Cone shaped, translucentCone shaped, translucent

55 to 90 mm55 to 90 mm22 in area in area

http://www.ghorayeb.com/AuricleEACAnatomy2.html

Three layersThree layers

Outer: Epidermis of EAMOuter: Epidermis of EAMInner: Mucosal lining of middle ear spaceInner: Mucosal lining of middle ear spaceMiddle: Collagen fibers, support for TM.Middle: Collagen fibers, support for TM.

Middle layer composed of two sets of Middle layer composed of two sets of fibers: fibers:

1.1. Radiates outward from centerRadiates outward from center

2.2. Concentric rings of fibersConcentric rings of fibers

Two regions in tympanic membrane:Two regions in tympanic membrane:

Superior region: Pars flaccida Superior region: Pars flaccida (defined by anterior and (defined by anterior and posterior malleolar folds and posterior malleolar folds and malleolar prominence)malleolar prominence)

Inferior region: Pars tensaInferior region: Pars tensa

Tympanic membrane, cont’d.Tympanic membrane, cont’d.

Umbo: Region of Umbo: Region of maximum concavitymaximum concavity

Position changes as EAM Position changes as EAM lengthens after birthlengthens after birth

Important landmarks Important landmarks visiblevisible

Tympanic membrane Tympanic membrane attached to ossicles.attached to ossicles.

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.html

Ossicles Ossicles

1.1. Malleus: HammerMalleus: Hammer

2.2. Incus: AnvilIncus: Anvil

3.3. Stapes: Stirrup Stapes: Stirrup http://www.ghorayeb.com/StapesPics.html http://www.ghorayeb.com/StapesPics.html

Head of malleus and body of incus located in Head of malleus and body of incus located in the epitympanic recessthe epitympanic recess

http://oto.wustl.edu/bbears/ossicle.htm http://oto.wustl.edu/bbears/ossicle.htm

http://audilab.bmed.mcgill.ca/~daren/3Dear/mid1.html

MalleusMalleus

9 mm long, 23-37 mg 9 mm long, 23-37 mg weightweight

Head with articular Head with articular facetfacet

NeckNeck

Anterior and lateral Anterior and lateral processesprocesses

Handle or ManubriumHandle or Manubrium

IncusIncus

About 23-32 mg About 23-32 mg weight weight

BodyBody

Short crus/process in Short crus/process in epitympanic recess, epitympanic recess, around 5 mmaround 5 mm

Long crus/process with Long crus/process with lenticular process, lenticular process, around 7 mmaround 7 mm

(Plural of crus: Crura)(Plural of crus: Crura)

StapesStapes 2-5 to 3.8 mm tall, 2.1 to 2-5 to 3.8 mm tall, 2.1 to

4.3 mg weight. Footplate 4.3 mg weight. Footplate area around 3.2 mmarea around 3.2 mm22

Head, with spine for Head, with spine for attachment of stapedial attachment of stapedial tendontendon

NeckNeck

Two bony crura, anterior Two bony crura, anterior and posteriorand posterior

Flat oval bone called Flat oval bone called footplatefootplate

Medial surface of footplate Medial surface of footplate fastened to wall of oval fastened to wall of oval window by annular window by annular ligament. ligament.

Unique connection allows Unique connection allows for rocking, rather than for rocking, rather than piston-like, movement of piston-like, movement of stapes.stapes.

Ossicular connectionsOssicular connections

Malleus: Manubrium of Malleus: Manubrium of malleus connects to umbo of malleus connects to umbo of TM.TM.

Incus: Head of malleus Incus: Head of malleus connects to body of incus connects to body of incus (incudo-mallear joint)(incudo-mallear joint)

Stapes: Inferior process of Stapes: Inferior process of incus connects to form incus connects to form lenticular process, which lenticular process, which connects to the stapes connects to the stapes (incudo-stapedial joint)(incudo-stapedial joint)

Footplate of the stapes Footplate of the stapes connects to the oval connects to the oval windowwindow

Ossicular connections, cont’d.Ossicular connections, cont’d.

Suspended in the Suspended in the middle ear cavity middle ear cavity by axial ligaments by axial ligaments and muscle and muscle tendonstendons

Middle ear Middle ear musclesmuscles

Tensor tympani Tensor tympani and stapediusand stapedius

Tensor tympani

Enters middle ear through anterior wall of tympanum.Enters middle ear through anterior wall of tympanum.

Connected to manubrium/neck of the malleusConnected to manubrium/neck of the malleus

Activated by the trigeminal nerveActivated by the trigeminal nerve

Muscle runs parallel and superior to osseous foundation Muscle runs parallel and superior to osseous foundation of the ET, separated by septum canalis musculotubarii)of the ET, separated by septum canalis musculotubarii)

Pulls malleus in anterior and posterior directionPulls malleus in anterior and posterior direction

Stapedius muscleStapedius muscle

•Tendon enters the middle Tendon enters the middle ear space through opening in ear space through opening in the posterior wall of the the posterior wall of the tympanum (pyramidal tympanum (pyramidal eminence)eminence)

•Attached to the head of the Attached to the head of the stapesstapes

•Activated by the facial Activated by the facial nervenerve

•Pulls stapes in the Pulls stapes in the posterior directionposterior direction