Topic Four - The Middle Ear Flashcards
Identify the different middle ear structures
Kahoot/Quizlet Quiz
What is the purpose of the middle ear?
The middle ear are crucial for impedance matching.
What is impedance?
A sound wave does not transfer easily into a medium of different properties (elasticity and density) than it was already traveling through (e.g., sound does not travel well from air into water).
The more dissimilar the density and elasticity of the mediums, the more sound if reflected at the boundary.
Without the middle ear, 99.9% of sound energy would be reflected off the cochlear.
What are the three ways in which the middle ear helps with impedance matching?
The middle ear acts as an acoustical transformer in three ways:
- Buckling of the tympanic membrane
- The lever ratio of the ossicles
- The area ratio of the tympanic membrane to the oval window
Order the different impedance matching processes from most to least impactful?
- Area ratio of the tympanic membrane to the oval window (+17 Pa)
- Lever ratio of the ossicles (+1.3 Pa)
- Buckling of the TM
Altogether, these processes result in an increase in 22.7 Pa or approx. 27 dB.
Describe how the lever ratio of the ossicles works?
As the long crus of the incus is 1.3 times shorter than the manubrium of the malleus, there is an increase in force.
Describe how the area of the TM to the oval window works?
The area of the TM is 17 times larger than the oval window.
How are the middle ear bones connected?
They are connected by synovial joints - this allows for a degree of slippage and the ability to conduct sound vibrations
How much does the malleus weigh?
Around 23mg
How much does the incus weigh?
Around 27mg
How much does the stapes weigh?
Around 2.5mg
What is the joint between the malleus and incus called?
The incudomalleal joint
What is the joint between the incus and stapes called?
The incudostapedial joint
