Anatomy and Physiology of the Ear

Question 1

What is the function of the Pinna

Answer 1

-Funnels sound into auditory canal -Externalisation of sounds -Localisation of sounds in the vertical plane

Question 2

What is the structure of the External Auditory meatus

Answer 2

Cartilaginous outer portion, bony inner portion 28mm long leads to tympanum membrane

Question 3

Function of the canal

Answer 3

-walls secret waxy cerumen- captures foreign bodies- self cleaning but wax can become compacted - Amplifying effect on sounds in speech frequency- resonance effects -protects sensitive machines of inner ear

Question 4

Function of the Austachian tube?

Answer 4

• equilibrate pressure in middle ear with atmospheric pressure -if middle ear was sealed- tympanic embrace would bulge in or out with ability to equilibrate

Question 5

Label the Diagram

Answer 5

Question 6

What is happening in the image and what are possibel causative agents?

Answer 6

• acute otitis Media
• 70% are bacterial- Streptococcus pneumonia- occur due to upper RT infefections spread via Eustachian tube
• up to 30% have non bacteria causes
• but viral infections makes Bacterial secondary infections more likely
  
  • otiits media occurs in 8% of mases

Question 7

Why are Otitis media infections more common in children

Answer 7

eustachian tube is more angled in adults- straighter in children

Question 8

What is happening in the below image?

Question 9

Name the ossciles

Question 10

Function of the Middle ear?

Question 11

Discribe how the ossciles act as levers?

Answer 11

between malleus and incus - suspended at a pivot point

malleus longer than incus- get lever affect- when malleus moves a given distacne with a given force- incus will also move wbut with greater force

Lever + pressure transfomred- increase in pressure x25 between tympanum and stapes footplate

Question 12

Label and name the muscles of the middle ear. and there function

Answer 12

• Tensor tympani- attaches to malleus- manidublar nerve
• Stapedius- emerges from pyramidal eminenece- smallest striated muscle in the body- facial nerve
• • Function is to provide output of middle ear reflec- prodtect form certian loud sound
    
    • contract and stifeen ossicular chain
    • cannot protect agaisnt very vbrielf impulsive noices
    • can protect agsint speaking- long louder noises

Question 13

What are the compartments of the inner ear

Answer 13

Scalar Vestiuli- seperated by the reisner membrane

scala media- seperated by basilar membrane

Scala tympani

Question 14

Label this cross section

Answer 14

Question 15

Describe the differences in the cochlear comparment fluids

Question 16

Label this cross section of the organ of corti

Answer 16

Question 17

Function of the organ of corti

Question 18

How many layers of inner and outer hair cells are there ?

Answer 18

1 layer of inner hair cells

3 layers of outer hair cells

Question 19

Describe how sound frequncies are sperated in the cochlear

Answer 19

Stapes footplate attaches to oval windown- assoicated with scala vestibuli

as the stapes vibrates at frequency of the soundp causes increase and decrease in pressure in the scala vestibuli- accoodates by round window bulges or buckles

Question 20

Describehwo pressure changes in the scaal vestibuli set up a travelling wave in the base of the cochlear toward the apex?

Answer 20

height/displacement of the wave changes depending on frequency

high frequency- base- position of maximum displacement of basiliar membrane

low frequency- apex possiiton of maximum displacement of the basiliar membrane

where hair cells are stimulates

Question 21

Describe frequneyc analysis by the cochlear

Question 22

Describe the movement of the basilar membrane relative to tectorial memvrane causing bending of hair stereocilliar

Answer 22

Hair cells stimulates in response to movement of basilar membrane

Tectorial membrane overlies hair cells

As the basilar membrane moves up and down the tectorial membrane shears across the top of the organ of corti. Leads to displacement of the stereocilia of the outer and inner hair cells.

This movement is then converted into an electrical signal

Question 23

Describe excitation of inner hair cells leading to transmission of electrical signal

Answer 23

Tips of the stereocilia, contain mechanically gated K+ channels

Stereocilia organised in height- between neighbouring stereocilia are links between, attached to the mechanically gated K+ channels

When neutral (vertical)

Some are open

When basilar membrane pushed upwards

Bend towards tallest in rank

Stretches links, causes maximal opening of K+ channels. More K+ enters cells and depolarise cell

When open allow K+ to move from K+ rich endolymph to move into the hair cell, down an electro- gradient

+80mV in the endolymph

-40mV in the hair cell

There is not an strong chemical gradient

Depolarisation

Leads to activation of voltage gated Ca2+ channels, Ca2+ enter cell, Vesicles of neurotransmitter release, auditory nerve fibres stimulates

NB- hair cells do not fire impulses- only nerve fibres do this. Graded potentials

Question 24

Describe how the bending of sterocillia affect polarisation

Answer 24

when bassilar membrane pushed upwards- bending towards the tallest cilia in rank- depolarisation

when bassiliar membrane psuhed downward- bedning towards shortest cilia in the rank- hyperpolarisation

Question 25

summarise the activation of hair cells

Question 26

What is the function of outer hair cells? name a key motor protien in OHC membrane

Answer 26

Outer hair cells

Change length of cells when stereocilia bend back and forth

Shorten and length in response to sound stimulation

Driven by motor protein OHC membrane- Prestin

Inject energy into organ or corti and amplify basilar membrane movement

Reason hearing is so sensitive- detect Basilar membrane movements in the nm range

Question 27

name durgss which damage the outer hair cells- the cochlear ampliers

Answer 27

amaged by some antibiotics- aminoglycosides

Other drugs, cisplatin, furosemide, salicylate (aspirin)

Ototoxicity- lead to hearing loss.

Question 28

describe the role of motor portein prestin- in amplification of basilar membrane

Answer 28

Elongation and shortening of outer hair cells, increase displacement of basilar membrane

Increased displacement of basilar membrane enhances sensitivity and frequency selectivity.

Question 29

what type of hearing loss is caused by damage to the inner ear