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Case 6 > Hearing and the Ear > Flashcards

Hearing and the Ear Flashcards

1
Q

What is human hearing range

A

20Hz- 20kHz

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2
Q

What is optimal human hearing

A

500-3000Hz

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3
Q

What happens with normal ageing

A

There is a decline in hearing sensitivity particularly at the high end

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4
Q

Which part of the ear contains goblet cells

A

The middle ear

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5
Q

Where can you get ear infections

A

In the middle ear as it contains goblet cells which are secretory

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6
Q

What is the inner ear responsible for

A

Sensory transduction

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7
Q

What do you use to view the tympanic membrane

A

Otoscopy/ auroscope

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8
Q

What is the tympanic membrane involved in

A

Conduction of vibration, therefore issues result in conduction related hearing loss

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9
Q

What is serous otitis media

A

A problem with drainage along the Eustachian tube often linked to respiratory infection, common in children

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10
Q

What do you do if children have issues with drainage along the Eustachian tube

A

Grommets are pushed through the tympanic membrane to provide an alternative drainage route. Grommets drop out spontaneously and the tympanic membrane heals

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11
Q

What are the ossicles

A

Malleus (hammer), incus (anvil), stapes (stirrup)

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12
Q

Describe impedance matching

A

The tympanic membrane has a large surface area but force generated by sound vibrations in the air is weak. Ossicles concentrate the force onto the smaller area of the oval window increasing the efficiency of transmission of the vibrations to the fluid filled inner ear which increases the sensitivity of the ear by a factor of 1000

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13
Q

What is oesteosclerosis

A

Calcification of the joints where the foot of the plate of the stapes inserts into the oval window. Runs in families, more common in females, age on onset typically 15-35, may be triggered by oregnancy

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14
Q

How you you treat osteosclerosis

A

Prosthetics are inserted via microsurgery to attempt to fix the problem

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15
Q

What are the 3 chambers of the cochlear

A

Scala vestibuli, scala media, scala tympani

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16
Q

Where is the basilar membrane

A

Located directly below the scala media

17
Q

What is the organ of corti

A

The hearing organ

18
Q

What are the hair cells in the organ of corti called

A

Stereocilia (are microvilli not cilia)

19
Q

What are the stereocilia held up by and why

A

The basement membrane so that they are in contact with the tectorial membrane

20
Q

What does the tectorial membrane do

A

Pushes cells from side to side

21
Q

Describe stereocilia

A

All different heights and reflex in one direction resulting in excitation onto the dendritic end of an axon

22
Q

What moves and what is fixed in the organ of corti

A

The basiliar membrane moves, the tectorial membrane is fixed

23
Q

Describe perilymph

A

Found in scala vestibuli and and scala tympani. Made up of everything apart from apical cells, Has high sodium concentration and low potassium concentration. Originates from blood plasma and CSF

24
Q

Describe endolymph

A

Found in scala media. Has a low concentration of sodium and high concentration of potassium. Originated from stria vascularis and contains and electrogenic Na+/K+ pump

25
Q

Compare the endolymph to the perilymph

A

Endolymphy is +80mv resulting in endocochlear potential

26
Q

What is Waardenburg syndrome

A

Cells that control K+ ion secretion into the stria vascularis fail to migrate into the tissue during development leading to deafness because there is no endocochlear potential

27
Q

What happens when sterocilia are deflected

A

K+ channels on the surface open and K+ flows into the cell due to the driving force of the endocochlear potential. This depolarises the hair cell which leads to transmitter release

28
Q

What are the stretch-gated channels on the stereocilia called

A

Tip links

29
Q

Describe inner hair cells

A

One row, 3,500 in number, role is pitch determination and they don’t regenerate

30
Q

Describe outer hair cells

A

Three rows, 12,000 in number, role is cochlear amplifier

31
Q

Describe cochlear amplifier

A

Outer hair cells contract when they are excited by the waves passing along the basilar membrane. When excited the outer hair cells depolarise resulting in them changing size and sinking. Effectively outer hair cells bounce on the basilar membrane in phase with the wave which increases the size of the wave on the membrane. Oscillations in phase result in a dramatic increase in amplitude. Depolarisation is brought about by electrical potential (controlled by sound loudness)

32
Q

Describe cochlear microphones

A

When the ear is damaged, the hairs may oscillate in the absence of external sound. This can cause the basilar membrane to vibrate and act as a loudspeaker that emits sound

33
Q

Describe difference tones

A

When two pure tones are presented to the ear, the movement of hair cells generate new waves that interact on the basilar membrane to produce a third peak- perceived as a sound by the brain, but this does not exist in the real world. The frequency of the difference tone:
ft = f2 – f1 e.g. for f1= 1335hZ and f2= 1600 Hz one solution is ft= 1600-1335 = 265 Hz. Difference tones can only be produced if the hair cells are functional

34
Q

How are difference tones used to diagnose cochlear deafness

A

Providing an objective measurement of hair cell damage, useful in patients who can’t give a subjective response (e.g. babies or dementia suffers). NB DPOAE- distortion product otoacoustic emissions. Two high tones produce a low tone, this can be used to test hair cell function

35
Q

When does conductive hearing loss occur

A

When there is a problem with the outer and/or middle ear

36
Q

When does sensori-neuronal hearing loss occur

A

When there is a problem with one or more of the cochlearm auditory nerve or central auditory pathways

Case 6 (10 decks)

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