Middle Ear Flashcards
Structures of middle ear
- Tympanic membrane
- Middle ear cavity
- Ossicular chain
- Eustachian tube
- Middle ear muscles
Middle Ear Cavity
Air filled space that is irregular in shape
Sections of middle ear
Tympanum (main cavity) and Epitympanum (attic)
Walls of Middle Ear Cavity
- Lateral
- Inferior
- Anterior
- Superior
- Medial
- Posterior
Lateral Wall (middle ear cavity)
Landmarks are:
- Tympanic membrane
- Chorda tympani (if severed, lose sense of taste)
Tympanic Membrane
Thin, elliptical shape, transparent, primary landmark of lateral wall
3 layers:
- cutaneous
- fibrous
- membranous
Layers of Tympanic Membrane
Cutaneous- lateral most layer made of epithelial tissue
Fibrous- middle layer, strong, contains 2 sets of fibers
Membranous- medial most layer, mucus membrane
Medial Wall (middle ear cavity)
Prominence of semicircular canals
Anterior Wall (middle ear cavity)
Eustachian tube!
Eustachian Tube
Air in the middle ear is refreshed by ET, helps with drainage from middle ear, opens fraction of a second at a time
When ET fails to open, there is negative pressure
Ossicular Chain
Suspended in middle ear cavity and held in place by a series of tendons and ligaments
- Malleus
- Incus
- Stapes
Middle Ear Muscles
- Tensor tympani: innervated by CNV (Trigeminal)
- Stapedial muscle: innervated by CNVII (Facial)
Optimal ME Conditions
- Equalized air pressure on both sides of TM
- Mobility of the moving parts of the middle ear (TM and Ossicular chain)
Tympanic Membrane Physiology
- Lies at angle at medial end of EAC
- Incredibly sensitive
- TM vibratory motion is different depending on the frequency of the incoming signal (lower freq moves more as a unit, higher freq moves segmentally)
- Sound undergoes transformation from acoustic energy to mechanical energy
Physiological Functions of the Middle Ear
- Overcome impedance mismatch
- Middle ear muscle reflex
- Ossicular chain movement
Impedance mismatch
Mismatch in impedance between the tissue filled and fluid filled inner ear and air filled outer ear and middle ear
Overcoming the impedance mismatch
- Area ratio hypothesis
- Lever ration hypothesis
- Curvature of the tympanic membrane
-With all 3, total amplification to overcome the IM is 33 dB
Area-ratio Hypothesis
Concentration of acoustic energy from a large area to a small area
-The pressure at the oval window is 17 times greater than at the tympanic membrane
Lever Ratio Hypothesis
Transfer of force from TM to stapes relies on ossicle movement
- Ossicles work as lever
- Pressure increase of 17 times greater from the area ration is multiplied by 1.3 from the lever ratio
Curvature of the TM
The TM tends to buckle as it moves, which causes the malleus to move with 2 times more force
Middle Ear Reflex
Clinical implications of acoustic reflex that helps protect inner ear- but reflex isn’t perfect
