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514 Mod 2


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What part of the skull is the auditory system located?
Temporal Bone
Label the "Peripheral" Auditory System diagram. See slides "The External and Middle Ears"
A- Pinna (outer ear)
B-External Auditory Meatus
C-Tympanic Membrane
D- Tympanic cavity
E-Eustachian tube
G-Cochlear nerve
H-Internal auditory meatus
I-Facial Nerve
J-Vestibular nerve
K-Semicircular canals
O-Temporal bone

That does the pinna do?
Funnel sound to the ear canal

Shape filters certain frequencies

The irregular shape makes it possible to determine the elevation of a sound source

Identify Crus of Helix, lobule, Tragus, Concha (cavum conchae), and helix on yourself
See slides.
What is the resonant frequency of the ear canal?
What is the average length of an adult ear canal?
2.3-2.97cm long
What are the average diameter and volume of the ear canal?
Diameter = 0.7cm
Volume = 1.0cm3

Describe the outer 1/3 (or half) of the ear canal.
Skin covered cartlidge contains glands that produce cerumen
Describe 2/3 (or half) of the inner ear
Skin covered temporal bone
Function of the outer ear pinna
Collect sound
Sensitive (earlobe)

By how much (in dB and how many factors) will the pinna amplify hearing sensitivity to a sound?

increase of 2 or 3 factors

For higher frequencies, how much gain in dBs will the ear canal give to an incoming sound wave. At what frequencies can we see the best gain

We can see the best gain at the resonant frequency of the ear canal which is 3600Hz. The gains will be lower higher and lower than this frequency.

Explain the Concha and Ear canal transfer function
It is the change in SPL from free-field to tympanic membrane. The total change is approximately 20dB because the Ear canal produces a gain of 6-10dB and the concha produces a gain of about 6-10dB.
Describe Head-Related Transfer function
If sound goes into left ear... the torso, head and external ear effects produce a sound shadow over the right ear for HIGHER frequencies (above 2000Hz).

This means there will be a difference in level of frequencies heard by each ear.

Remember higher frequencies are important for speech.

What percentage of reflection occurs at the eardrum for higher frequencies?
30-70% is reflected for higher frequencies at the eardrum
What is the resonant frequency of an ear canal that has a canal length of 2.4cm?
Using c=345m/s... it is 3594Hz.


At which structure does the Middle Ear begin?
Tympanic Membrane
The middle ear is an air filled cavity of about _ cm3
2 cm3
What are the ossicles comprised of? Which bone is the largest? Which bone is the smallest?
Incus = largest
Stapes = smallest

Label the Otoscopic view...see notes from 518 for good handout
-name: Head of malleus, pars flaccida, manubrium of malleus,
umbo, fold.

See handout
If the arm of the malleus is at a one oclock it the right or left ear?
What is the thickness of the eardrum?
What is the threshold of the eardrum for feeling?
.1mm threshold of feeling
Refer to Ossicular chain and label the diagrams
see handout
What are the 3 functions of the middle ear?
1) Area advantage
2)Lever action
3) TM buckling

Explain the area advantage of the middle ear
Oval window is smaller than Tympanic membrane.

Because p = force/area... aka the area of the oval window is smaller than the TM... the Pressure will be higher at the oval window.

It will be between 15-20 times higher pressure at the oval window. (around 25dB).

Ossicles act as a lever system. How many times bigger will the output force be than the input force?
1.3-3 times bigger (2.3dB)
How much of a pressure increase does the TM buckling action produce?
2 times

or increase of 6dB

What is the total gain across the middle ear?
17 * 1.3 * 2 = 44.2 times
What muscle is involved with the Acoustic Reflex? What average sound level (dB)does it contract? Which frequencies is it most effective at reducing?
- Stapedius muscle
- Contracts to sounds greater than 75 dB
-Most effective at reducing the level of sounds less than 2000Hz

What is the Reflex latency range for the Acoustic Reflex?
For the Tensor Tympani, what is the:
- Origin
- Insertion
- Action
- Nerve

Mode of activation in human:?

Origin - cartliginous and bony margins of eustachian tube

Insertion - Handle of Malleus (via processus trochleariformis)

Action - Protects and critically damps ossicular chain

Nerve - Trigeminal nerve

Mode of activation in human: non-acoustic stimulus

For the Stapedius muscle, what is the:


mode of activation in human:

Origin - The pyramid (post wall of middle ear)

Action - Protects and critically damps ossicular chain

Insertion - Neck of stapes

Nerve - Facial nerve in middle ear

mode of activation in human: acoustic and nonacoustic stimuli

What is the motion of the ossicles when normal and at high levels of sound?
Normal - swinging door (hinge)

High levels - rocks around the axis (see saw motion)

What are the functions of the Eustachian tube?

What is the average length of the eustachian tube?
What is the main function of the Eustachian tube in terms of pressure in the outer and middle ear? What is this important for?
It keeps the middle ear pressure equal to the outer ear (atmospheric pressure).

This is important for maximum transfer of sound energy to inner ear.

What is the impedance formula?
See handout
What is admittance?
Admittance (Y) is the reciprocal of impedance: a measure of the ease with which energy flows into a system. AKA compliance.
What is reflex decay?
Can be caused by sluggish measurement system (space between stimulus onset and beginning of response)...looks sloped.
What are the BC mechanisms/routes?
- radiation of sound into the canal (then via the normal route)

- inertial movement of the ossicles

-skull vibration causes CSF pressure fluctuations which is transferred to the cochlear fluids

-DIRECT cyclic compression of the cochlear fluids by skull vibration!

Does the cochlea respond identically to both BC or AC or both?
What is atresia
malformation of the external ear (pinna)
What effect does a perforated TM have on the amplitude of vibration of the ossicles?
As the frequencies decrease, the loss in amplitude increases
The operation of repairing eardrums is called?
Ears without a TM, Malleus, and incus show the greatest loss at what frequency? (referring to the slides...n=5)
1000Hz...although there is a general loss everywhere.
What will the tympanogram look like with someone who has ossicular discontinuity
the height of the peak will be much higher and the peak will be shifted to the left (negative value).
What is the most complex mechanical apparatus in the human body?
Where is the cochlea ?
Inside the temporal bone
Note the location of the Osseous spiral lamina. See 2nd handout and label figure on page 1.
see handout
How many turns does the cochlea make? What is the diameter? What is the uncoiled length?
2 5/8th turns
2mm diameter
35mm uncoiled length

Label the cochlear ducts.
See diagram in handout
Point to the scala tympani, scala media, and scala vestibuli
See Inner Ear schematic diagram in notes
What is the vestibule connected to? What does the vestibule contain?
It is connected to the 3 semi-circular canals (angular acceleration). It is also connected to the scala vestibuli of the cochlea.

It contains the utricle and saccule (gravity up/down and linear acceleration)

Be able to draw and label cross section of cochlea. Practice.
See notes (handout)
What is the function of the stria vascularis?
It contains blood vessels and controls metabolism of cochlea

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