1.51 The Ear

Question 1

What are the functions of the pinna?

Answer 1

Funnels sound in the ear canal
Externalisation of sound
Localisation of sound in the vertical plane - above and below head

Question 2

What is the function of the auditory meatus (ear canal)?

Answer 2

Walls secrete waxy cerumen - self cleaning
Captures dust and foreign antibodies
Some amplifying effects

Question 3

What is the air pressure in the middle ear?

Answer 3

The same as the external air pressure because of the auditory tube

Question 4

Whats is the function of the middle ear?

Answer 4

To overcome the air - fluid mismatch
This is possible because the tympanic membrane is greater than the foot of the stapes so the pressure at the stapes is much higher

Question 5

Why is a middle ear needed?

Answer 5

without a middle ear there would poor transfer of sound from air to fluid

Question 6

What is the malleus and what is it attached to?

Answer 6

The malleus is the first ear ossicle, and it is attached to the tympanic membrane and also to the incus

Question 7

What are the muscles of the middle ear and what is their function?

Answer 7

Tensor tympani and stapedius - they control stiffness of the ossicular chain.

Question 8

What are the innervations for tensor ty,pain and stapedius?

Answer 8

Tensor tympani - V3

Stapedius - VII

Question 9

What are the other two middle ear ossicles?

Answer 9

Incus - middle

stapes - oval shaped window that connects to the inner ear

Question 10

What is the middle ear reflex?

Answer 10

Contraction of the stapedius muscle
e.g rock concert
The middle ear reflex protects from against loud sounds, not if they are too fast for the reflex to activate - gun shot

Question 11

What is Rinne’s test?

Answer 11

negative result is when the patient hear the bone conduction longer or louder than the air conduction - hearing loss

Question 12

Where do the two middle ear muscles attach?

Answer 12

Tensor tympani - malleus

Stapedius - stapes

Question 13

What is located in the petrous part of the temporal bone?

Answer 13

Inner Ear

Question 14

What is the petrous part of the temporal bone referred to as?

Answer 14

The osseous labyrinth - filled with perilymph

Question 15

What is the name of the membronous sack in the osseous labyrinth?

Answer 15

Membronous labyrinth - filled with endolymph

Question 16

Through which structures does the middle ear communicate with the inner ear?

Answer 16

Oval window - stapes

Round window - filled with membrane

Question 17

What happens when the stapes pushes the oval window?

Answer 17

The fluid in the inner ear is compressed, this can displace the membrane in the round window - acts as a pressure release

Question 18

What are the two components of the inner ear?

Answer 18

The cochlea - hearing

The vestibular apparatus - balance

Question 19

What are the three parts of the cochlea?

Answer 19

Scala vestibuli, scala tympani and scala media (duct)

Question 20

What are the scala vestibule and tympani filled with?

Answer 20

perilymph (Na+)

Question 21

How are the scala vestibule and tympani separated to the scala media?

Answer 21

Two membranes

Vestibular and basal membrane

Question 22

What is the scala media filled with?

Answer 22

Endolymph (K+)

Question 23

What happens to the cochlea when sound hits the inner ear?

Answer 23

Stapes hits oval window - displaces perilymph
Transferred to the the scala tympani and vestibuli
Fluid displaces basilar membrane
Stereo cilia are deflected because of their resistance against the tectorial membrane
This result in ionic conductance
Stimulates bipolar neurons - to CNS

Question 24

Where are the cell bodies of the bipolar neurones found?

Answer 24

Central portion of spiral duct - spiral ganglia

Question 25

How are different wavelengths differentiated in the cochlear?

Answer 25

The movement of Specific sections of the basilar membrane and its neuroepithelial hair cells occurs for specific wavelengths of fluid - tonotopic - intensity is also o determined at this point

Question 26

Where in the cochlear are high and lower pitches deflect?

Answer 26

High pitches - max displacement on the basilar membrane near the oval window
Low pitches - max displacement basilar membrane near the end of the tube (helicotrema)

Question 27

When there is bending towards the tallest stereocillium, what does that do the potential?

Answer 27

Increased inflow of potassium ions - depolarisation - neurotransmitter release - nerve fires

Question 28

What happens when there is bending towards the shortest stereocillium?

Answer 28

Decreased inflow of potassium ions - hyper polarisation - no neurotransmitter

Question 29

What is the function of inner hair cells?

Answer 29

Release neurotransmitter - activate cochlear fibres associated with region where basilar membrane displacement is at its maximum - neurotransmitter release & excitation of auditory nerve fibres - K+ inflow

Question 30

Whats the function of outer hair cells?

Answer 30

K+ inflow - change length when hairs bend back and forth - - driven by preston in OHC membrane amplify basilar membrane movement - sensitive hearing

Question 31

What can be damaged by certain drugs (ototoxic)?

Answer 31

some antibiotics - aminoglycosides - furosemide

Question 32

What is one quick and easy test for hearing?

Answer 32

Oto-acoustic emmission - play sound into the ear - echo back - echo means cochlear is healthy - good for babies