physiology of hearing and balance

Question 1

what is sound?

Answer 1

a pressure wave caused by oscillating molecules that are set in motion by a vibration

Question 2

what does frequency dictate?

Answer 2

pitch

Question 3

what does amplitude dictate?

Answer 3

intensity

Question 4

what frequencies do humans perceive?

Answer 4

20Hz to 20,000Hz

Question 5

what is an audiogram?

Answer 5

it covers hearing range

Question 6

what is the role of the external ear?

Answer 6

it is shaped to receive sound, and there is huge variation in size of the external ear

Question 7

what is microtia?

Answer 7

Microtia is a congenital deformity where the pinna (external ear) is underdeveloped. can be bilateral/unilateral

Question 8

what is anotia?

Answer 8

completely underdeveloped pinna

Question 9

what is ear canal atresia?

Answer 9

Atresia is the absence or closure of the external auditory canal.Males are more affected than females, and interestingly, the right ear is more commonly affected in unilateral cases.

Question 10

what does the ossicular chain act as?

Answer 10

a piston or lever arm with varying efficiency depending on frequency of sound transmitted

Question 11

what is the tympanic membrane: oval window ratio?

Answer 11

18:1 (impedance matching air to liquid) leading to a pressure gain of x22

Question 12

what is the ratio of malleus handle to incus long process?

Answer 12

1.3:1

theoretical mechanical gain of 34dB but actually nearer to 20-25dB

Question 13

what is the function of the eustachian tube?

Answer 13

Ventilation pathway for middle ear mucosa
Bony & cartilaginous portions

Resting state of cartilaginous tube is closed but opened by tensor veli palatini & levator palatine muscles
‘equalise ears’
Dysfunction leads to middle ear negative pressure

it keeps the eardrum full of gas - fluid cant conduct sound

it balances ear pressure by opening up

Question 14

what is the function of the oval and round windows?

Answer 14

Two openings of the cochlea to the middle ear.
In phase movements of windows
Permit transmission of pressure wave in enclosed canal & vibration of the basilar membrane

Question 15

how is the waves transmitted to the perilymph?

Answer 15

As round window goes in, pressure window
Diff. frequencies of sound are perceived at different areas of the cochlea
Due to shape of basilar membrane – movement of the membrane of the basilar membrane that causes unrolling of the cochlea

Question 16

what is the role of the inner ear?

Answer 16

receiver/transducer

curved spiral lamina
2 1/2 turns around central modiolus
Need to consider the ultrastructure of cochlea

Question 17

where is the endolymph and perilymph located?

Answer 17

Scala media (endolymph) suspended in between scala tympani & scala vestibuli (perilymph)

there is Different ionic composition between the endolympoh and perilymph. High potassium and low sodium in the endolymph and opposite for perilymph

Question 18

what is the schematic of the cochlear?

Answer 18

Coiled tubes of liquid
Scala media (endolymph) suspended in between scala tympani & scala vestibuli (perilymph)
Actively maintained in these concentrations to ‘power’ the sensory cells

Question 19

what is the organ of corgi?

Answer 19

the receptor of auditory stimuli, situated on the basilar membrane of the cochlea

inner hair cells perceive sound, depolarize and send Paps to the brain

modulating activity, efferent