Middle Ear Anatomy
Which ossicle is attached to the tympanic membrane and which ossicle is attached to the oval window?
The malleus is attached to the TM & the stapes is attached to the oval window.
What 3 factors contribute to middle ear impedance?
Friction, mass, and stiffness.
What 2 muscles are located within the middle ear cavity?
Stapedius muscle and tensor tympani
A patient has a Type B tympanogram with large ear canal volume, what does this suggest?
A tympanic membrane perforation.
What component of middle ear impedance is associated with energy loss that affects sound transmission across all frequencies?
Friction
What are the 3 layers of the tympanic membrane?
An outer epidermal layer, a middle fibrous layer, and an inner mucosal layer.
Why does the middle ear need an impedance matching system?
To overcome the impedance mismatch and improve transmission of sound energy from air to fluid.
The tensor tympani is innervated by which cranial nerve?
V
A patient has a Type Ad tympanogram. What does this indicate about middle ear mechanics, and what pathology could cause it?
Increased middle ear compliance/decreased stiffness of the system. Example pathology would be ossicular discontinuity.
Above approximately 4000 Hz, which impedance mechanism is dominant?
Mass
Name any 3 landmarks/components of the tympanic membrane.
Cone of light, annulus, pars flaccida, pars tensa, umbo, radial fibers, circular fibers.
The middle ear transfer function is greatest at which frequency?
1kHz
What are the 2 major functions of the eustachian tube?
Equalization of middle ear pressure and allowing aeration/drainage of the middle ear.
What type of hearing loss would you generally expect when a middle ear pathology prevent sound from being efficiently transmitted to the inner ear?
Conductive hearing loss
Below approximately 1000 Hz, which impedance mechanism is dominant?
Stiffness
What are the mastoid air cells and what is their purpose?
Mastoid air cells are hollowed out air spaces within the temporal bone and provide a pressure relief system for the middle ear.
What is the estimated total average middle ear impedance matching boost in dB?
33dB
Describe the differences between adult and children eustachian tubes.
Children are more susceptible to infection due to shorter narrower and more horizontally orientated eustachian tubes.
A patient has eustachian tube dysfunction. Which tympanogram would you expect if middle ear compliance is otherwise normal?
Type C (negative pressure)
Power reflectance is generally lowest at which frequency region?
1-4kHz
Describe the eustachian tube's osseous and cartilaginous portions and their typical state. Additionally, what is the junction point between these portions called?
The 1/3 of the ET that is osseous is typically open, the remaining 2/3 cartilaginous portion is usually patent or closed and opens upon swallowing. The junction point is the isthmus.
Name the 3 major mechanisms responsible for middle ear impedance matching.
The area advantage, curved membrane buckling, and ossicular lever action.
Contraction of the stapedius muscle does what? Additionally, what test is associated with this muscle?
Increases stiffness between the stapes foot plate and oval window. Acoustic reflex threshold testing measures the lowest stimulus level at which involuntary contraction of the stapedius muscle occurs.
A patient has a Type As tympanogram. What does this indicate about middle ear mechanics and what pathology could cause it?
This indicates increased stiffness of the system/reduced middle ear compliance. Example pathology would be otosclerosis or stapes fixation.
What does wideband reflectance assess?
Middle ear energy transmission (stiffness and mass impacts) and reflection across .5-8000Hz frequency range