Middle ear

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

Middle ear cavity 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 Lateral wall or membraneous wall: Formed by TM Medial wall or labyrinthine wall: Promontory (outer wall of inner ear) Contains oval and round windows Anterior wall or carotid wall Posterior wall or mastoid wall Inferior wall or jugular wall Superior wall or tegmental wall

Tympanic membrane Located in a bony groove Held in place by fibers and cartilage Cone shaped, translucent 55 to 90 mm2 in area http://www.ghorayeb.com/AuricleEACAnatomy2.html

Tympanic membrane, cont’d. Composed of two sets of fibers: Radiates outward from center Rings of fibers Two regions in tympanic membrane: Superior region: Pars flaccida Inferior region: Pars tensa

Tympanic membrane, cont’d. Umbo: Region of maximum concavity Tympanic membrane attached to ossicles. http://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.html

Ossicles Malleus: Hammer Incus: Anvil Stapes: Stirrup http://www.ghorayeb.com/StapesPics.html Head of malleus and body of incus located in the epitympanic recess http://oto.wustl.edu/bbears/ossicle.htm http://audilab.bmed.mcgill.ca/~daren/3Dear/mid1.html

Malleus Head Anterior and posterior processes Handle or Manubrium

Incus Body Short crus/process Long crus/process (Plural of crus: Crura)

Stapes Head or capitulum Two bony crura Flat oval bone called footplate