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special senses > physiology of hearing > Flashcards

physiology of hearing Flashcards

1
Q

what happens to pressure waves as you get further away?

A

dissipates

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2
Q

what is frequency?

A

number of (vibrations) cycles per second, perceived as pitch, measured in Hz

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3
Q

what is the frequency range of human hearing?

A

20-20000Hz but diminishes with age

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4
Q

what is intensity?

A

what we perceive as loudness, the amount of energy transmitted throughout the wave

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5
Q

what is the sound threshold?

A

quietest sound that can be heard at each frequency

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6
Q

how is sound threshold plotted?

A

audiodiagram

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7
Q

how do we measure how much energy Is in a sound wave in dB SPL (sound pressure level)?

A

dB SPL audiogram, this gives us curves that are hard to interperate

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8
Q

why is a logarithmic scale used to measure what we can hear?

A

loudest sound we can hear is about 100 trillion times louder than the quietest

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9
Q

how much is an increase in 10dB perceived as?

A

twice as loud, 10 times the sound energy

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10
Q

what does the outer ear consist of?

A

pinna (auricle)
ear canal (external acoustic meatus)

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11
Q

what does the middle ear consist of?

A

tympanic membrane
ossicles

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12
Q

what does the inner ear consist of?

A

cochlea
vestibule

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13
Q

why do we have 2 ears?

A

-allows us to localise sound in a horizontal plane
-primarily due to inter aural time difference
-also aided by the difference in loudness

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14
Q

what does the pinna do?

A

collects the sound
-amplifies and filters the frequency of the sound
-filters some high frequency sound behind you compared to in front (therefor can differentiate between front and back)
-similar occurs with up and down

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15
Q

what is the structure of the ear canal like?

A

only hair and wax in the outer 1/3
simple tube, sound resonates in the tube

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16
Q

what is the function of the ear canal?

A

simple tube, sound resonates in the tube
-this allows for amplification
adds up to 10dB of amplification of speech frequencies

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17
Q

what are the 3 bones of the ossicles?

A

malleus
incus
stapes

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18
Q

what is the function of he ossicles?

A
  • 3 bone system which is much better at transmitting sound (especially high frequency) than a single bone (seen in the animal kingdom)
  • Large tympanic membrane, with a large footplate (of bone) which transmits sound to much smaller area (the oval window) - this amplifies sound (by at least 25dB/17x)
  • The lever action of the bone system also allows some amplification (1.3x)
  • The main benefit however of having 3 bones comes from the ability to extend our range of hearing much further into higher frequencies
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19
Q

what is the stapedius reflex muscle?

A

contracts (connected to the stapes) when you hear a very large sound and protects the cochlea. It gets tired easily however

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20
Q

what is the tensor tympani?

A

runs along the eustachian tube and connects to the malleus. Prevents blowing out of the tympanic membrane although the exam answer is that it protects against large sounds

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21
Q

what is the eustachian tube ?

A
  • Connects the nasopharynx to the middle ear
  • Allows air to enter the middle ear to equalise pressure
  • Closed at rest, opens during swallowing and valsalva
  • By allowing the pressure to be the same internally and externally the tympanic membrane can vibrate
  • Dysfunction leads to a blocked feeling and poor hearing
  • Air filled space that communicates with the nose via the eustachian tube
22
Q

why would hearing be lost relating to the ear canal?

A

wax, foreign body, congenital atresia

23
Q

why would hearing be lost relating to the tympanic membrane?

A

perforation

24
Q

why would hearing be lost relating to the ossicles?

A

congenital fusion, damage from infection

25
Q

why would hearing be lost relating to the middle ear space?

A

fluid instead of air

26
Q

what is the cochlea?

A

Contains sensory epithelium for hearing - the Organ of Corti

27
Q

how do vibrations enter the cochlea?

A
  • Oval window faces into the vestibule
  • Vestibule contains sensory epithelia for saccule and utricle (to do with balance)
  • Vestibule leads to the scala vestibuli (upper cochlear duct)
  • Pressure waves travel along the scala vestibuli (around helicotrema) then back through scala tympani (lower cochlear duct)
  • Waves terminate at the round window - this is important to allow the vibrations to pass through the fluid as the round window can bulge out (as fluid is incompressible)
28
Q

what controls the electrolyte composition of endolymph?

A

stria vascularis

29
Q

what Is the arrangement of the organ of corti?

A
  • Basilar membrane on the floor and the tectorial membrane on the top. The tectorial membrane houses the auditory hair cells
  • 1 row of inner hair cells and 3 rows of outer hair cells
  • These hair cells sit on the basilar membrane
  • Coming away from these hair cells are nerve fibres which will form the auditory nerve. the cell bodies of these are in the spiral ganglion in the middle of the cochlea
30
Q

what is the structure of the basilar membrane of organ of corti?

A
  • The basilar membrane is stiff and light at the oval window end and is flexible and heavy towards the apex of the cochlea
  • When there are sound vibrations in the scala tympani and scala vestibuli, it sets up vibrations in the basilar membrane
  • Some portions will vibrate better at different frequencies as the resonant frequency changes over its length
    • Low frequencies will vibrate better toward the apex of the cochlea and higher frequencies closer to the round window
31
Q

what are hair cells?

A
  • Epithelial in origin, resembing cells that line the stomach
  • Stereocillia form a bundle at the apical pole of the hair cell
  • The tallest cilium is called the kinocilium
  • When you push the stereocillia towards the kinocilium you get depolarisation of the cell
  • When you push the kinocilium towards the stereocilia you get hyperpolarisation
32
Q

what is the receptor that picks up vibrations of the basilar membrane and transducer the mechanical energy to electrical energy?

A

the inner hair cell

33
Q

what causes depolarisation and hyper polarisation?

A

Depolarisation is due to the influx of potassium when the stereocilia push towards the kinocilium.

Closing these channels is responsible for hyperpolarisation.

34
Q

what os the neurotransmitter at the basal membrane?

A

glutamate

35
Q

what are the outer hair cell rows?

A
  • These are motile
  • When the basilar membrane vibrates, the OHCs change shape and stiffness (contracting)
  • This feeds energy back into the basilar membrane (reverse transduction)
  • This acts as an amplifier, increasing amount of vibration on basilar membrane (cochlear amplifier)
  • Also improves frequency selectivity as it amplifies the vibrations on the point of the basement membrane that is maximally vibrating and dampens the vibrations on the other parts of the membrane to allow for increased frequency discerning
36
Q

how does cochlear hearing loss occur in babies?

A
  • Otoacoustic emission test used for newborns
  • OHCs move in response to a noise, and we can hear them moving
  • ## This is a quick, objective screening test for hearing loss in babies
37
Q

how can hearing be lost due to hair cells?

A
  • Infections, ototoxins, noise - furosomide, gentamycin. cisplatin
  • Aging, “wear and tear”
  • Sensorineural hearing loss
38
Q

how can hearing be lost due to inner hair cells?

A
  • no signal to the brain
  • Infinite dB loss in hearing (potentially)
39
Q

how is hearing lost due to loss of outer hair cells?

A
  • Basilar vibration is insufficiently amplified
  • 50dB loss in hearing
  • Loss of sound discrimination
40
Q

what are hearing aids?

A

-microphone-amplifier-speaker
-they make everything louder
-this is all you need to correct conducting hearing loss

41
Q

what are the limitations to hearing aids?

A

helpful but doesn’t completely alleviate the disability of sensorineural hearing loss
-loss of discrimination
-loss of dynamic function
-central processing effects

42
Q

what structure allows for pitch discrimination?

A

basilar membrane

43
Q

what is the accuracy of pitch discrimination limited by?

A

wideness of the region (place code) that vibrates
the outer hair cell helps to stop this but there are other features of the vibration that helps discern pitch

44
Q

what other features help discern pitch?

A

-hair cells creating a temporal code
-frequency of signals sent down the axon from the vibration of the cilia in time with the frequency of vibration of the pressure wave
only works for low pitched noises however high pitched noises you cannot generate impulses quick enough due to the refractory period

45
Q

why is it difficult to endode for a pitch in high pitched noises?

A

you cannot generate impulses quick enough due to the refractory period

46
Q

what are cochlear implants?

A

hearing implants directly in the cochlea to stimulate the spiral ganglion cells If there is severe hearing loss due to loss of hair cells

47
Q

what is the vestibule?

A

contains sensory structures for balance and head movements

48
Q

what is the pathway for the central processing of sound?

A
  • First order neurones in the spinal ganglion of the cochlea
  • Travel in CN VIII though internal acoustic meatus to cerebello-pontine angle
  • Synapse on cochlear nuclei (junction of medulla and pons)
  • After this it is bilateral
  • From there via Olive and Trapezoid body (pons) to inferior colliculus (midbrain)
  • Medial geniculate body (thalamus)
  • Superior temporal gyrus (cortex) - consciously appreciate the sound
49
Q

why does damage to the CNS not tend to produce hearing loss?

A

above the cochlear nuclei, representation is bilateral

50
Q

what is the Eustachian tube?

A

connects middle ear with nasal sinus cavity. helps to balance pressure in the middle ear (commonly felt as ears popping) and drain fluid from the middle ear.

51
Q

what can be done if the mid and inner ear system works fine but outer doesn’t?

A

can get a device that vibrates the skull and conducts the bones

52
Q

Before vibrations reach scala vestibuli, what structure must vibration be conducted through?

A

Eustachian tube

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