514 Mod 2
Terms
undefined, object
copy deck
- 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
F-Cochlea
G-Cochlear nerve
H-Internal auditory meatus
I-Facial Nerve
J-Vestibular nerve
K-Semicircular canals
L-Stapes
M-Incus
N-Malleus
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?
- 3600Hz
- 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
Localization
Resonator
Protection
Sensitive (earlobe) - By how much (in dB and how many factors) will the pinna amplify hearing sensitivity to a sound?
-
6-10db
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
-
6-10dB
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.
f=c/4L - 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?
-
Malleus
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 position...is it the right or left ear?
- Right
- What is the thickness of the eardrum?
- .1mm
- 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?
- 50-150ms
-
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:
Origin
Action
Insertion
Nerve
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?
-
Ventilation
Drainage
Protection - What is the average length of the eustachian tube?
- 35mm
- 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?
- Yes
- 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?
- Tympanoplasty
- 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?
- cochlea
- 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