Hearing and the Ear

Question 1

What is human hearing range

Answer 1

20Hz- 20kHz

Question 2

What is optimal human hearing

Answer 2

500-3000Hz

Question 3

What happens with normal ageing

Answer 3

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

Question 4

Which part of the ear contains goblet cells

Answer 4

The middle ear

Question 5

Where can you get ear infections

Answer 5

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

Question 6

What is the inner ear responsible for

Answer 6

Sensory transduction

Question 7

What do you use to view the tympanic membrane

Answer 7

Otoscopy/ auroscope

Question 8

What is the tympanic membrane involved in

Answer 8

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

Question 9

What is serous otitis media

Answer 9

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

Question 10

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

Answer 10

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

Question 11

What are the ossicles

Answer 11

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

Question 12

Describe impedance matching

Answer 12

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

Question 13

What is oesteosclerosis

Answer 13

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

Question 14

How you you treat osteosclerosis

Answer 14

Prosthetics are inserted via microsurgery to attempt to fix the problem

Question 15

What are the 3 chambers of the cochlear

Answer 15

Scala vestibuli, scala media, scala tympani

Question 16

Where is the basilar membrane

Answer 16

Located directly below the scala media

Question 17

What is the organ of corti

Answer 17

The hearing organ

Question 18

What are the hair cells in the organ of corti called

Answer 18

Stereocilia (are microvilli not cilia)

Question 19

What are the stereocilia held up by and why

Answer 19

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

Question 20

What does the tectorial membrane do

Answer 20

Pushes cells from side to side

Question 21

Describe stereocilia

Answer 21

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

Question 22

What moves and what is fixed in the organ of corti

Answer 22

The basiliar membrane moves, the tectorial membrane is fixed

Question 23

Describe perilymph

Answer 23

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

Question 24

Describe endolymph

Answer 24

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

Question 25

Compare the endolymph to the perilymph

Answer 25

Endolymphy is +80mv resulting in endocochlear potential

Question 26

What is Waardenburg syndrome

Answer 26

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

Question 27

What happens when sterocilia are deflected

Answer 27

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

Question 28

What are the stretch-gated channels on the stereocilia called

Answer 28

Tip links

Question 29

Describe inner hair cells

Answer 29

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

Question 30

Describe outer hair cells

Answer 30

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

Question 31

Describe cochlear amplifier

Answer 31

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)

Question 32

Describe cochlear microphones

Answer 32

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

Question 33

Describe difference tones

Answer 33

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

Question 34

How are difference tones used to diagnose cochlear deafness

Answer 34

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

Question 35

When does conductive hearing loss occur

Answer 35

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

Question 36

When does sensori-neuronal hearing loss occur

Answer 36

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