Physiology of hearing and balance

Question 1

Middle ear

• purpose
• mechanism by which sound is transferred?

Answer 1

• acts as an amplifier

- pressure hitting the ear drum is transferred onto a smaller area (impedance matching air to liquid

Question 2

Eustachian tube

• what is it?
• opened by what muscles?
• function?
• dysfunction can cause?

Answer 2

• ventilation pathway for middle ear mucosa with bony and cartilage portions
• tensor veli palatini & levator palatine
• equalises ear pressure
• middle ear negative pressure i.e. glue ear

Question 3

oval window and round window

• what are they?
• what do they do?

Answer 3

-openings of the cochlea into the middle ear

-Oval window
allows the transmission of waves into perilymph causing the basilar membrane to vibrate

round window
acts ad pressure reliever to dampen vibrations after they have had an effect

Question 4

Inner ear

• purpose
• hearing component of middle ear?

Answer 4

• acts as receiver and transducer for sound

- cochlea

Question 5

Structure of the cochlea

• look in de picture in notes and name
• where is perilymph located?
• where is endolymph located?
• describe the different composition of ^^, why?

Answer 5

-pretty
scala vestiboli
scala tympani
scala media
basilar membrane
vestibular membrane
spiral ligament
spiral organ

• in scala vestibuli and scala tympani
• scala media

-perilymph= high Na and low K
endolymph= low Na and high K
to power sensory cells

Question 6

Organ of corti

• name the components
• where do the membrane attach?
• how is the nerve impulse transmitted?

Answer 6

-tectorial membrane
basilar membrane
outer hair cells
inner hair cells

-TM-scala vestibuli
BM- scala tympani

-movement of hairs

Question 7

Hair cell function

• name?
• what is it?
• arrangement?

Answer 7

• stereocilia
• transduction= to convert mechanical sending force to electrical impulse
• stereocilia arranged in height order and move in the same direction

Question 8

what is meant by the tonotopic organisation of the cochlea?

Answer 8

base responds to high frequency and the apex responds to low frequency

Question 9

describe the pathway of nerve impulse from the organ of corti

Answer 9

organ of corgi depolarises & fires, stimulating the 8th CNand then the central pathways & culminated in the superior temporal gyrus

Question 10

name the system involved in maintaining balance (4)

Answer 10

ears
eyes
proprioception
cardiac

Question 11

name the parts of the semicircular canals(6)

• what are otolith organs and function?
• what sits in the ampulla of the SC?

Answer 11

anterior/posterior/horizontal
saccule
utricle
Ampulla

-macula of the utricle and sacule
have stereocilia projecting upwards into a gelatinous matrix with otoconia (Cacarbonate crystals)
movement perceived by the hyperpolarisation/depolarisation o the stereocilia

-Cupula, it os deflected by the movement of endolymph, this causes the steriocilia to deflect and hyper/depolarisation occurs

Question 12

what is the vestibule cochlear reflex?

• failure of this causes?
• pathology that can cause this?

Answer 12

• when the head moves laterally it turns your eyes more in the opposite direction to maintain the same position
• spontaneous nystagmus
• vestibular shwannoma