Hearing part 2

Question 1

What are the three components of the outer ear?

Answer 1

Pinna
Auditory canal
eardrum/tympanic membrane

Question 2

What is the function of the pinna?

Answer 2

helps focus sound towards ear canal
Helps determine direction of sound because it is highly asymmetrical

Question 3

How long is the auditory canal?

Answer 3

3 cm long

Question 4

What is the function of the auditory canal?

Answer 4

protects eardrum
Enhances frequencies of 1000 Hz to 5000 Hz due to resonance

Question 5

What is the function of the eardrum?

Answer 5

transmits sound as vibration to middle eat by flexing back and forth

Question 6

What is another name for the eardrum?

Answer 6

tympanic membrane

Question 7

What are the components of the middle ear?

Answer 7

ossicles - malleus, incus, stapes

Question 8

What happens in the middle ear when sound pressure causes eardrum to vibrate?

Answer 8

Eardrum causes ossicles to vibrate:
Malleus connected to incus — connected to stapes

stapes transmits vibrations to oval window of inner ear

Question 9

What is the purpose of the middle ear?

Answer 9

amplifies sounds by a factor of 10 to 50 from air pressure in outer ear to liquid pressure in inner ear

Question 10

How does the muddle ear amplify sounds?

Answer 10

Concentrates pressure from large eardrum onto small stapes footplate
Uses mechanical leverage to generate large force on stapes footplate from small force on eardrum

Question 11

What are the two muscles of the inner ear?

Answer 11

Tensor tympani and stapedius

Question 12

Where are the two muscles in the inner ear connected to?

Answer 12

stapedius muscle is connected to stapes
tensor tympani muscle is connected to malleus

Question 13

What is the function of the auditory reflex?

Answer 13

Protects inner ear and reduces interference from internal sounds (speech, chewing etc)

Question 14

How does the auditory reflex work?

Answer 14

Stapedius contracts in response to high sound levels (amplitude) and own speech - holds bones still so less force gets passed to inner ear

Reduces transmission of low frequency/high amplitude sounds

Protects inner ear and reduces interference from internal sounds (speech, chewing, etc)

Question 15

What are the two components of the inner ear?

Answer 15

semicircular ducts and cochlea

Question 16

What are the semicircular ducts involved in?

Answer 16

balance and equilibrium

Question 17

What are the three semicircular ducts called?

Answer 17

anterior, lateral, posterior

Question 18

What is the cochlea?

Answer 18

coiled snail-like structure that contains sensory receptors for sound

Question 19

What is the size of the cochlea?

Answer 19

2 mm wide but 35 mm long uncoiled

Question 20

What are the three main compartments of the cochlea?

Answer 20

Scala vestibuli (vestibular duct)
Scala tympani (tympanic duct)
Cochlear partition (cochlear duct)

Question 21

What does the cochlear partition contain?

Answer 21

sensory receptors

Question 22

Is the cochlea filled with liquid?

Answer 22

yes

Question 23

Where are the three parts located in the cochlea?

Answer 23

Scala vestibuli is located on the top
Scala tympani is located on the bottom
Cochlear partition is in the middle

Question 24

What organ does the cochlear partition contain that runs along the length?

Answer 24

Organ or corti

Question 25

What does vibration of oval window by stapes do?

Answer 25

sends pressure waves down scala vestibuli to apex and back up scala tympani towards round window

Question 26

What are the three parts of the cochlear partition?

Answer 26

Tectorial membrane (upper) Organ of corti Basilar membrane

Question 27

What are the two parts of the organ or corti?

Answer 27

Inner hair cells Outer hair cells

Question 28

Describe the inner and outer hair cells?

Answer 28

Inner is one row of cells an the cilia are free Outer is 3 rows of hair cells and the cilia are embedded in tectorial membrane - move with membrane

Question 29

What does the round window do?

Answer 29

moves back and forth and absorbs sounds so they don't go back

Question 30

How many inner and outer hair cells do we have in the ear?

Answer 30

Not many 3500 inner hair ells and 12000 outer hair cells - easily damaged

Question 31

What do pressure waves in the cochlea cause?

Answer 31

Basiliar membrane to move up and down Tectorial membrane to move back and forth Cilia of hair cells to bend

Question 32

Where are hair cells embedded? What do they have coming in and out of them?

Answer 32

in tissue afferent and efferent nerve endings

Question 33

What are the cilia of hair cells connected by?

Answer 33

Tip-links

Question 34

Where does transduction occur?

Answer 34

in hair cells

Question 35

What does bending of cilia to the right and left do?

Answer 35

Bending of cilia to the right causes K+ ion channels to open Bending of cilia to the left causes K+ ion channels to close

Question 36

How does transduction occur in the hair cells?

Answer 36

Increased membrane potentials due to K+ entering cause neurotransmitter release on auditory nerve fibers

Question 37

How are K+ channels opened?

Answer 37

tip links pull on it to open the mechanically gated channels

Question 38

What part of the ear is most succeptible to damage from from loud sound?

Answer 38

tip-links because they can break from too much movement

Question 39

How does phase locking work?

Answer 39

Movement of cilia follows changes in pressure Thus, neurotransmitter release follows changes in pressure Thus, action potentials in auditory nerve are synchronized with sound waves

Question 40

How does phase locking work at low frequencies?

Answer 40

firing can occur with every wave --> fires only at peak

Question 41

How does phase locking work at high frequencies?

Answer 41

firing is intermittent because a single hair cells cannot hit all peaks but when you combine the firing of many hair cells you get phase locking

Question 42

What is the main message of Bekesy's place theory of hearing?

Answer 42

location of maximum firing indicates frequency

Question 43

According to Bekesy's theory how is the base of the basiliar membrane (by stapes)?

Answer 43

three to four times narrower than at apex 100 times stiffer than at apex

Question 44

How does Bekesy's place theory of hearing work?

Answer 44

sound causes travelling waves along basilar membrane whose position of maximum displacement depends on frequency Location of peak displacement has highest firing rate by auditory nerve cells - indicates frequency

Question 45

How does the cochlear amplifier work for neural response (Bekesy missed this)?

Answer 45

Basilar membrane is not a passive object Outer hair cells change shape to amplify and focus motion of basilar membrane - actively interact with sound

Question 46

What happens when hair cells elongate? What about when they contract?

Answer 46

amplify the motion of the hair cells - increasing firing stiffen against pressure waves

Question 47

How do hair cells elongate and contract?

Answer 47

They have efferent and afferent connections - incoming signals tell it to stiffen or relax

Question 48

How is frequency represented along the basilar membrane?

Answer 48

sound causes waves to travel along basilar membrane Location of waves peak depends on frequency

Question 49

Where are low (25 Hz) and high frequency represented along the basilar membrane (1600 Hz) ?

Answer 49

Low is closer to apex and high is closer to base

Question 50

How does the basilar membrane respond to pure tone frequencies increasing?

Answer 50

as frequency goes up the location of maximum displacement moves towards base

Question 51

What does basilar membrane activation look like for sound composed of two frequencies (1000 and 2500 Hz)?

Answer 51

gets broken up based on frequency so there are two areas of maximum displacement along membrane

Question 52

What do complex sounds look like on basilar membrane?

Answer 52

many different locations of max displacement

Question 53

What does a tonotopic map show?

Answer 53

location of maximum response as a function of frequency, not location highest frequencies at base Lowest at apex

Question 54

What do frequency tuning curves of auditory nerve cells show?

Answer 54

each auditory nerve cell responds to certain frequencies, based on position along cochlea

Question 55

Does each auditory nerve cell only respond to one frequency?

Answer 55

No a range of frequencies

Question 56

Why is the cochlear amplifier very important for frequency tuning? What would happen if the outer hair cells were destroyed?

Answer 56

if they were destroyed there would be a very broad tuning having the cochlear amplifier allows for more specific tuning

Question 57

What is the function of the ear?

Answer 57

Transduces sound waves into a tonotopic neural signal