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BIOPHYSICS > LECTURE 9 (Sound hearing) > Flashcards

LECTURE 9 (Sound hearing) Flashcards

1
Q

What is sound?

A

A mechanical wave that propagates in discrete medium (gas, liquid, solid substance and plasma) but not in a vacuum

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2
Q

What are the properties of sound?

A
  • Characterised by properties of mechanical waves
  • Considered as mechanical compression-extension
  • Wave causes alteration in pressure in elastic medium and oscillation of constitutive particles
  • Expressed by its propagation in space and time
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3
Q

Which properties should be considered when studying sound wave?

A
  • Properties of elastic medium
  • Elasticity
  • Deformability
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4
Q

What are the four fundamental states of matter?

A
  • Solid
  • Liquid
  • Gas
  • Plasma
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5
Q

What are the properties of Plasma?

A
  • Created by heating a gas or subjecting it to a strong electromagnetic field (applied with a layer/microwave generator at temp above 5000 degrees c) -> decreases/increases the number of electrons in atoms/molecules -> creates ions + accompanied by dissociation of molecular bonds if present
  • Responds strongly to electromagnetic fields (charged carriers make it electrically conductive)
  • No definite shape or definite volume
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6
Q

What does propagation of sound wave in discrete medium induce?

A

Physical displacement of particles of medium around equilibrium condition

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7
Q

What is the difference between Longitudinal sound waves and Transverse sound waves?

A

Longitudinal sound waves = Fluctuation of changeable pressure around equilibrium condition determined by local compression and extension

Transverse sound waves = Waves determined by changeable deformation of solid material (layers sliding) in perpendicular of waves propagation

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8
Q

What is the difference between Simple tone and Complex tone?

A

SIMPLE TONE
- when the acoustic spectre of musical sound includes only one frequency
- may vary with intensity
- obtained by camertone + human whistling

COMPLEX TONE
- acoustic specter has 2 or ore frequencies - MAIN TONE (fundamental) is simple tone with lowest frequency + OVERTONES
- obtained by any musical instrument + human speech apparatus

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9
Q

What is Acoustic specter/Harmonic specter of a complex sound?

A

The sum of frequencies participating in superposition

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10
Q

What is the difference between a musical sound/complex tone and noise?

A

Musical sound/complex tone = When acoustic specter is intermittent, including only certain discrete values of frequencies

Noise = A sound which includes continuous sequence of frequencies

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11
Q

What are sound waves?

A

Longitudinal waves where compressions and rarefactions are moving and local oscillation of pressure occurs

Explanation: Due to propagation of sound waves in discrete medium, particles perform oscillation motion

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12
Q

What does white spots density show?

A

Density of wave propagation medium and wave pressure

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13
Q

What is wavelength?

A

The distance between compressive peaks

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14
Q

Describe the graph for sound

A
  • X axis = Time
  • Y axis = Wave disturbance
  • Soft sound -> Smaller amplitude
  • Louder sound -> Bigger amplitude
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15
Q

What are the physical properties of sound waves?

A
  • Frequency
  • Wavelength
  • Period
  • Amplitude
  • Intensity
  • Propagation velocity
  • Acoustic impedance
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16
Q

What is Amplitude?

A

The maximum amount of displacement of a particle on the medium from its rest position and is perceived as “loudness”

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17
Q

What is Frequency?

A

The number of peaks that go by a fixed point in one second

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18
Q

What is the equation for Sound wave pressure?

A

P= ραV

α = medium particle motion velocity
ρ = density of a medium
V = wave propagation velocity
P = wave pressure

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19
Q

What is Impedance?

A

A physical characteristic of wave propagation area depending on density of the medium and its elastic property and is independent on the wave frequency

Z= ρV

ρ = density of area
V = velocity of wave propagation

1 Rail= 1 kg/m3*m/sec= 1 kg/m2
sec

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20
Q

What is Intensity?

A

An energetic feature of sound wave and is an energy that is transferred per area through propagation region of space per unit of time

I = Pα

P = wave pressure
α = velocity of particle

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21
Q

What is Velocity?

A

Velocity of sound wave propagation depends on the propagation medium, pressure and temperature

V = √E/ρ

E = Elastic factor (Young’s modulus)
ρ = Density

[speed is low in air and highest in bone]

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22
Q

What is the Bulk modulus?

A

The ratio of the change in pressure to the resulting fractional change in volume

B = - DP/ DV/V

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23
Q

What is the equation that shows that the speed of sound depends on temperature?

A

V = (331m/s)√T/273K

24
Q

What is the average Intensity of a wave on a given surface?

A

The rate at which energy flows through the surface divided by the surface area

I = power/area

[the direction of energy flow is perpendicular to the surface at every point]

25
Q

What is Intensity level/Decibel level?

A

The relative intensity of a sound

26
Q

What are the levels that humans can hear?

A
  • Normal levels = 2500-3000 Hz
  • Lower bound of intensity (10-12 w/m2) called “hearing limit” -> human’s acoustic organ cannot perceive a sound which has less intensity
  • Upper bound of intensity (10 w/m2) called “pain sensation bound” -> sound that exceeds this limit is perceived as pain and does not perceive as sound
27
Q

What is Loudness?

A

A subjective characteristic of sound that represents the objective intensity of a sound

L= 10lg(I0/It)

  • A unit of loudness is “Bel”
  • 1 Bel is sound intensity that exceeds 10-fold acoustic limit I0
28
Q

What is Sound volume (tone)?

A

A subjective characteristic of sound that is related to frequency -> The higher the sound frequency is, the higher the pitch is and vice versa

29
Q

What is Timbre?

A

A subjective characteristic of sound depending on its acoustic specter

Explanation: Human’s acoustic organ is able to distinguish two sounds with the same height and loudness if they belong to different sources of a sound

30
Q

What is the difference between Ultrasound and Infrasound?

A

Ultrasound = sound above 20 kHz

Infrasound = sound below 20 Hz

31
Q

What is important about the Human’s speaking apparatus?

A
  • Vowels (A,E, I, O & U) sounds are formed only due to oral cavity volume
  • Consonant sounds require tongue and lips movement
  • Characteristics of acoustic sounds depends on VOLUME and FORM of the oral cavity
32
Q

How does the human body produce sound?

A

1) POWER SOURCE (diaphragm + ribcage)
2) SOUND
(air from lungs pushed up the TRACHEA and reaches LARYNX which contains the vibrating vocal chords that produce sound)
3) ARTICULATION
(tongue, soft palate and lips modify the sound to produce words)

33
Q

What is the Ear’s main function?

A
  • Receive the acoustic waves
  • Amplify the intensity
  • Analyse the frequency and structure of the wave
  • Reject random background noise

[mechanical waves that ear perceives is called “acoustic waves”]

34
Q

What are the three sections of the human ear?

A
  • OUTER EAR - long ear canal terminated by the eardrum
  • MIDDLE EAR/TYMPANIC CAVITY - contains three small bones (OSSICLES with connecting tube to mouth cavity)
  • INNER EAR/LABYRINTH - spiral shaped, fluid filled tube system (cochlea) with internal organ of Corti

[Eardrum = separates outer ear from middle ear, Oval window = between middle ear and inner ear]

35
Q

How do we hear?

A

1) Sound waves enter your outer ear and travel through the EAR CANAL to your EARDRUM
2) EARDRUM vibrates and sends vibrations to three tiny bones in MIDDLE EAR
3) Bones in middle ear amplify the sound vibrations and send them to the INNER EAR/COCHLEA -> Sound vibrations activate tiny hair cells in inner ear which release NEUROCHEMICAL MESSENGERS
4) AUDITORY NERVE carries electrical signal to brain which translates it to sound

36
Q

What is the importance of the Oval window being much smaller than the ear drum?

A

Causes increase in intensity of sound wave

37
Q

How does the body protect against loud sounds?

A

Muscle system of middle ear decreases transmission intensity of bone complex in order to protect middle ear against loud sounds -> Muscle constrict before you start talking and in response to loud noise

38
Q

What did Helmholtz establish?

A

Basilar membrane in the inner ear is narrow and stiff near the oval window and relatively floppy on the other side -> Each segment of basilar membrane oscillates for a particular frequency of sound wave -> Hair cells oscillate with high frequency near the oval window + low frequency on the other end of basilar membrane

39
Q

What is Phonocardiography?

A

A method to record the sounds produced by the heart valves, to visualise them on a PC and analyse them in order to discover dysfunction of a valve

[routinely used to record pulse wave pressure and sound propagated in cardiovascular system]

40
Q

What can cause acoustic disorders?

A
  • Loud sounds can cause drum membrane destruction
  • Damage of basilar membrane of inner ear or hair cells
  • Restriction of movement of ossicular apparatus
  • Inner ear infections cause hair cells damage
41
Q

Describe how psychoacoustic tests and perception ability is used to test for hearing loss

A

Test vibrator is placed behind the ear or on the forehead and patient is checked for perception ability for frequencies and signals propagated by the vibrator

42
Q

When is hearing compensation impossible?

A

If helix nerve fiber is damaged due to disease

43
Q

When can ultrasound hearing occur?

A

If ultrasound is fed directly into the skull bone and reaches the cochlea without passing through the middle ear

44
Q

What is the Hypersonic effect?

A

Even without consciously hearing it, high frequency sound can have a measurable effect on the mind

45
Q

What is a sound wave typically produced by?

A

Piezoelectric transducer encased in a probe

46
Q

What is a Piezoelectric Element?

A

A material that generates an electric charge when mechanically deformed

[when an electric field is applied to piezoelectric materials, they mechanically deform]

47
Q

When is the Piezoelectric effect reversible?

A

In materials exhibiting the direct piezoelectric effect, production of an electric potential when stress is applied also

48
Q

What effects does Ultrasound have on living tissue?

A
  • Mechanical
  • Thermal
  • Physico-chemical
49
Q

What are the different characteristics of Ultrasound?

A
  • Reflection: ultrasound waves can reflect from external and internal surfaces
  • Scattering: us waves can scatter due to inhomogeneties within different tissues
  • Transmission: us passes through tissue as a mechanical pressure wave
  • Absorption: acoustic energy is absorbed by frictional and viscous forces
  • Refraction: us waves can change direction, especially when they pass between two different media
  • Attenuation: loss of acoustic energy as us wave passes through tissue
  • Doppler shift: us waves change frequency when they encounter moving surfaces
50
Q

What are the two sources of sound beam attenuation?

A

Reflection & Scatter

51
Q

What are the two types of reflections?

A
  • Specular reflection (one direction)
  • Diffuse reflection (multiple directions + low amplitude)

[Acoustic reflection is determined by differences in acoustic impedance]

52
Q

What are the advantages and disadvantages on Ultrasound?

A

ADVANTAGES
- real-time images
- portable
- low cost
- does not use harmful ionising radiation

DISADVANTAGES
- limits on field of view
- difficult imaging structures behind bone + air
- dependence on skilled operator

53
Q

What is the difference between Lower and Higher frequencies?

A

LOWER FREQUENCIES
- less resolution but image deeper into body

HIGHER FREQUENCIES
- higher resolution but limitation of depth of sound wave into body (since more readily absorbed in tissue)

54
Q

What is the Doppler effect determined by?

A

The movement towards each other or either wave source and receiver

55
Q

What is the Doppler effect used for in medicine?

A

To measure the flow velocity of blood in vessels and the heart with ultrasound

56
Q
A

BIOPHYSICS (15 decks)

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