The ear and hearing

Question 1

What are the two systems of the ear?

Answer 1

• Vestibular system

- Auditory system

Question 2

What is the function of vestibular system in information?

Answer 2

Inform the brain of the position of head and body and how they are moving

Question 3

Function of vestibular system

Answer 3

Balance

Question 4

Function of auditory system info

Answer 4

Detect sounds
Locate them in space
Identify sound nuances

Question 5

Function of auditory system

Answer 5

Hearing

Question 6

What does pitch (tone) depend on?

Answer 6

Frequency

Question 7

What does intensity (loudness) depend on?

Answer 7

Amplitude

Question 8

What does timbre (quality) depend on?

Answer 8

Overtones

Question 9

What is sound amplitude expressed in>

Answer 9

db

Question 10

What is sound amplitude expressed in>

Answer 10

db

Question 11

What is the auditory threshold?

Answer 11

0db

Question 12

Auditory system pathway

Answer 12

Sound waves move tympanic membrane ➡
Tympanic membrane moves ossicles ➡
Ossicles move oval window membrane ➡
Movement in oval window moves fluid in cochlea ➡
Fluid in cochlea induces response in sensory neurons

Question 13

Auditory system stimulus pathway

Answer 13

Auditory Receptors (Cochlea) ➡ Brainstem ➡ Thalamus (Medial geniculate nucleous-MGN ➡ Primary Auditory Cortex

Question 14

Pressure in oval window vs tympanic membrane

Answer 14

Greater pressure (force/surface) in the oval window than in the tympanic membrane,

Question 15

What happens after a loud sound? (attenuation reflex)

Answer 15

The brain will diminish hearing sensitivity by tensing the muscles → impairment of amplification system

Question 16

Attenuation reflex

Answer 16

• Protection (delayed)
• Adaptation to loud sounds
• Not hearing our own speech

Question 17

Where are malleus and stapes linked and how?

Answer 17

Link to skull by muscles

Question 18

What communicates at apex?

Answer 18

Scala vestibuli and scala tympani

Question 19

Where does perilymph flow from?

Answer 19

From vestibuli to tympany when stapes taps the oval window

Question 20

Where does endolymph flow?

Answer 20

Inside the scala media

Question 21

Basilar membrane at apex is ..

Answer 21

Wider and more flexible

Question 22

When perilymph is displaced…

Answer 22

Displaces endolymph (vestibular membrane very flexible) and generating waves in the basilar membrane.

Question 23

Where are high frequencies detected?

Answer 23

Near oval window narrow and stiff

Question 24

Where are low frequencies detected?

Answer 24

Near apex wide and flexible

Question 25

Frequency discrimination in | the cochlea diagram

Answer 25

Question 26

Inner ear: Transduction pathway

Answer 26

A. Upward displacement of basilar membrane creates a shearing force that leads to lateral displacement of the stereocilia B. Mechanical displacement of the stereocilia in a lateral direction cause depolarization of the hair cell. C. Downward displacement of the basilar membrane creates shearing force that results in lateral displacement of the stereocilia in the opposite direction hyperpolarization of the hair cell.

Question 27

What does perilymph have a similar composition to?

Answer 27

Cerebral spinal fluid

Question 27

What does perilymph have a similar composition to?

Answer 27

Cerebral spinal fluid

Question 28

Endolymph in scala media ion concentration

Answer 28

High K+ and low Na+

Question 29

Ion channel in inner ear transduction

Answer 29

Mechanically gated ion channel

Question 30

How is the inner ear mechanically gated ion channel connected?

Answer 30

In different stereocilia by an elastic filament (tip-link)

Question 31

Cilia bending in one direction in inner ear

Answer 31

Channel opens: K+ influx and cell depolarization

Question 32

Cilia straight in inner ear

Answer 32

Channel semi-closed: K+ influx at resting potential

Question 33

Cilia bending in opposite direction in inner ear

Answer 33

Channel closed: cell hyperpolarization

Question 34

What does channel opening lead to and why?

Answer 34

K+ influx because of the exceptionally high [K+] in the endolymph!

Question 35

What do most of fibres in auditory nerve innervate?

Answer 35

Inner hair cells, and the contribution of outer cells is somehow small

Question 36

What are fibres in auditory nerve

Answer 36

Axons of Spiral ganglion cells

Question 37

Amplification system by outer hair cells

Answer 37

* Sound depolarizes the outer hair cell * That change in membrane potential induces the cell to shorten or lengthen (electromotility) * The change on length amplifies the movement of the basilar membrane

Question 38

NB!! Mechanism of hearing

Answer 38

1. Sound waves induce oscillation in the tympanic membrane 2. Pressure waves are transmitted through the ossicles to the oval window 3. Pressure on the oval window induces movement of the basilar membrane 4. Displacement of the basilar membrane depolarizes hair cells (sensory cells) 5. Depolarization of outer hair cells change their morphology, amplifying the signal 6. Depolarization of inner hair cells induce neurotransmitter release 7. Neurotransmitter evokes AP in the auditory (cochlear) nerve

Question 39

What are hair cells innervated by?

Answer 39

An efferent fibre

Question 40

Acetylcholine function in hearing

Answer 40

Can induce hair cell hyperpolarization, reducing the sensitivity of the cochlea locally

Question 41

When is a cochlear implant useful?

Answer 41

When cause of deafness is sensory-neural (damage/death of hair cells but mostly functioning auditory nerve)

Question 42

NB! Describe cochlear implant

Answer 42

Headpiece with microphone (converts sound into electrical signals), digital processor, a radio transmitter (conveys a digital code to an internal receiver). The receiver will send electrical impulses through electrodes that enter the cochlea and stimulate the auditory nerve → from base to apex - Uses natural tonotopy to differentiate frequencies

Question 43

Cochlear implant diagram

Answer 43