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AUDI 514 - Hearing Science > Lecture 3 > Flashcards

Lecture 3 Flashcards

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1
Q

How is the temporal bone related to the ear structure?

A

Mastoid protrudes behind pinna.
External auditory meatus - inner 1/3 of ear canal and tympanic membrane
Internal auditory meatus - pass from inside skull to structures of the inner ear and face.

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2
Q

What are the general structures from the outer to the inner ear?

A

Pinna, Concha - Ear Canal - Tympanic Membrane - Middle Ear (malleus, incus, stapes) - Oval Window - Cochlea

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3
Q

What is the role of the pinna?

A

To collect sound and funnel it to the ear canal. Shape filters certain frequencies.
Protects, localizes.
Has some resonance.
KNOW: Conchae, Crus of Helix, Tragus, Helix**

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4
Q

What are some characteristics of the ear canal?

A

2.3-2.97cm long, volume 1.0cm cubed, resonant frequency of 3.6kHz.
Protects the ear drum
Outer 2/3 is skin covered cartilage; contains glands that produce cerumen
Inner 1/3 is skin covered bone (temporal bone)

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5
Q

What is the pinna doing as it collects sound? What is the process?

A

Area gets larger, pressure drops with every doubling of sound. Collecting from larger area and funnelling force into a smaller area. Pressure is dissipated (sound pressure = F/A)
As surface area gets smaller, the reverse transfer of the inverse law occurs.
The energy twice as far from the source is spread over 4x the area, hence 1/4 the intensity.

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6
Q

What is the outer ear transfer function?

A

Taking sound energy at different frequencies and multiplying it by a resonant factor of the ear canal. Naturally filters certain frequencies based on physical properties.
Different frequencies have different transfer characteristics of tube (resonant)
Waves reflect back, standing wave set up as sound is amplified by the structure.

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7
Q

What is the resonance of the ear canal?

A

Due to tube like structure, has 3kHz resonance, and other peaks due to resonant property of the ear canal.

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8
Q

Where does the middle ear begin and what are the structures involved?

A

Begins at the TM, air filled cavity. Contains the TM, the eustachian tube, and the malleus, incus, and stapes; stapedius and tensor tympani muscles.

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9
Q

What are the characteristics of the tympanic membrane?

A 
Mass 14mg (to transfer higher frequencies), diameter 7.5-9mm, area 0.5-0.9cm^2. 
3-4 skin layers thick. Buckling action of TM during movement = 2x - due to attachments at the manubrium and malleus.
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10
Q

What are the 3 ossicles?

A

Malleus, incus, stapes.

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11
Q

What are the characteristics of the malleus?

A

Largest of 3 ossicles. Has head, neck, lateral process and manubrium.

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12
Q

What are the characteristics of the incus?

A

Articulates with posterior surface of the head of the malleus. Has body, short and long process, lenticular process, and articulate facet for malleus.

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13
Q

What are the characteristics of the stapes?

A

Is the smallest bone in the body. Has capitulum which articulates with the incus, a neck, 2 crura, and footplate.

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14
Q

Function of the middle ear: what is the impedance-matching transformer?

A

Lever action - large/weak vibrations at eardrum are converted into smaller, stronger vibrations at the oval window.

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15
Q

How does the middle ear function work?

A

Larger area membrane that imparts its energy onto the smaller surface = higher pressure. Area difference from the TM to oval window = 17:1. Increase in sound pressure by 25dB.
Because pressure= F/A, if we have the same force over smaller area, pressure higher at output.

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16
Q

Middle ear function: how do the bones affect this?

A

Angles of bones exist for a reason- small force = lots of torque on point of bones. With a long lever you don’t need much force to lift an object.
Small force applied at membrane, transferred into large force on stapes.
Malleus and incus act as a lever system so output force is higher than the input force - 1.3x to 3x.
Length determines amount of torque = force applied.
Short leg of lever = less distance = more force.
Long leg of lever = more distance = less force.

17
Q

How does the TM buckling affect the middle ear function?

A

Manubrium pulls TM in, causing buckling. There is a greater deflection of force and snapping back due to elastic properties which increase the amplitude by 2x.
Resonant properties of mass elasticity system that adds to the system at specific frequencies.

18
Q

What is the total gain across the middle ear from the output force of the stapes to the input force at the tympanic membrane?

A

Area difference between TM and oval window = 17x.
Lever action of malleus and incus = 1.3x
Buckling action of TM during movement = 2x.
Total = 44.2 times
Gain in dB is 20log44.2/1 = 33dB.

19
Q

Muscles of the middle ear: what is the origin, insertion, action and nerve of the tensor tympani?

A

Origin: Cartilaginous and bony margins of eustachian tube
Insertion: Handle of malleus (via processus trochleariformis)
Action: Protects and critically damps ossicular chain)
Nerve: Trigeminal (V)

20
Q

Muscles of the middle ear: what is the origin, insertion, action and nerve of the stapedius?

A

Origin: The pyramid (post wall of middle ear)
Insertion: Neck of stapes
Action: Protects and critically damps ossicular chain. Reduces transfer of energy to cochlea
Nerve: Facial (VII), in middle ear

21
Q

What is the acoustic reflex?

A

Stiffness of ossicular chain increased, and magnitude of vibrations transmitted to cochlea decreased. Good at reducing the level of low frequency sounds, more than high frequency sounds.
Might serve to protect the cochlea form at least some sounds that might damage it.
Shifting transfer function by stiffening up ossicular chain

22
Q

How does the stapes contribute to the movement of the ossicles?

A

Lever action - pivotal door hinge rocking motion - transfer of energy. Rotate around a centre point (better energy transfer); seesaw rotational aspect

23
Q

What does the eustachian tube do and where does it go?

A

Does ventilation, drainage, and protection. Tube to the back of the pharynx, maintains pressure in the middle ear cavity.
If there is a pressure difference between the external ear and here - impedance difference.

24
Q

How does the eustachian tube equalize pressure?

A

Has connections to the facial muscle to stretch the tube (like chewing gum); activates the facial muscles and creates a vent. Want it open for air flow.
Ear popping is when air moves along the tube and causes “pop” in TM.
If clogged, cannot equalize pressure.
Ear infection pain due to pushing out of the TM.

25
Q

Why is it important to keep an equal pressure in the ear canal and middle ear?

A

The function of the EU tube is important for maximum transfer of sound energy to the inner ear. More compliance means more motion for a given sound pressure, causing larger response in the cochlea.

26
Q

What is admittance?
What happens with change in stiffness/mass?

Refer to 518 for characteristic tymps

A

The reciprocal of impedance: a measure of the ease with which energy flows into a system (AKA compliance).
Changes in stiffness: greater effect on low frequencies
Changes in mass: greater effect on higher frequencies
Negative pressure at peak = tympanic membrane compliant
Flat line - full impedance
Volcano - perforation

27
Q

What is seen in the acoustic reflex?

A

Impedance changes at the input of the middle ear resulting from activation of the reflex

28
Q

What is the middle ear function/purpose?

A

Overcome air-fluid impedance mismatch; compensate for changes in atmospheric pressure; direct sound stimulation to oval window; protection against intense sound (ME reflex and ossicular motion); reduce distortion (ME muscles and ligaments hold ossicles tight)

29
Q

Air and bone conduction: how is the middle ear/cochlea involved?

A

Middle ear takes air conduction and transfers to the cochlea.
Bone conduction is energy across the bone through to the cochlea

30
Q

What is the route/mechanism for BC?

A

Radiation of sound into the canal; intertial movement of the ossicles, skull vibration causes CSF pressure fluctuations which is transferred to cochlear fluid, direct cyclic compression of the cochlear fluids by skull vibration

31
Q

What are some implications of abnormal ears?

A

Congenital atresia = pinna not formed
Impacted cerumen = problem conducting sounds into TM
TM perforation = pressure build up too long in EU tube
Ossicular discontinuity = when there is no resistance, full compliance (also sign of perforation)

AUDI 514 - Hearing Science (15 decks)

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