Hearing and Vestibular System

Question 1

What consists of the Outer ear and what is it’s function

Answer 1

1- Pinna ( auricle )
2- ear canal
3- Tympanic membrane ( ear drum )
Function : direct sounds to the eardrum

Question 2

What does the Middle ear consist of , and what is it’s function

Answer 2

Ossicular lever system ( 3 bones )  
1- Malleus ( hammer ) 
2- Incus ( anvils ) 
3- Stapes ( stirrup ) 
Function : transmit vibration from the tympanic membrane to the inner ear

Question 3

What does the inner ear consist of and what is it’s function

Answer 3

1- cochlea : hearing
2- vestibule & semicircular canals: balance
Function: conversion of mechanical vibrations to electrical signals

Question 4

What are the smallest muscles int he body and which cranial nerve controls them

Answer 4

The tensor timpani and strapedius muscles controlled by cranial nerve 7

Question 5

Explain in detail the process of critical damping in the middle ear ( of the bones + muscles )

Answer 5

1- Critical damping :
Ear drum resonates to a variety of frequencies , but also must stop resonating when frequency ends. The ear drum is connected to the Malleus, stapes and incus to stop vibrating as soon as sound stops. Allows ear drum to be critically damped.

2- Protective Reflex :
Tensor timpani and stapedius muscles contract reflexly before a sound occurs. Tighten up to prevent vibrations from being too loud and damaging hair cells of cochlea.

Question 6

What is a situation in which the Reflex of the Tensor timpani and stapedius muscle might not work ?

Answer 6

Reflex takes longer than 150 milliseconds, therefore loud sounds with rapid onset can cause damage to cochlea since reflex wouldn’t have had time to tighten muscles ( ex: gun shot sound )

Question 7

Why is the ear affected in Bell’s palsy

Answer 7

Cranial Nerve 7 is affected which controls the muscles in the ear. One of the clinical signs of Bells palsy is that you can hear sounds more loudly in the affected ear, long term might cause hearing damage

Question 8

What are the 3 jobs of the middle ear

Answer 8

1- Critical Damping
2- Amplification
3- Impedance Matching

Question 9

Explain the process of amplification of the middle ear

Answer 9

Lever action gives 130% of force at the oval window at the stapes of the force at the tympanic membrane.
The tympanic membrane is a large area vibrating the oval window, a small area. = greater pressure = amplification

Question 10

Explain the process of Impedance Matching of the middle ear

Answer 10

Because more force is generated at the oval window , over a smaller area , there is greater pressure. This means humans can vibrate same magnitude in liquid as air. Amplification is necessary in order to vibrate at same frequency in liquid cochlea.
= Air impedance matches liquid impedance

Question 11

What does the cochlea consist of ?

Answer 11

1- 3 chambers : Scala vestibuli , scala media , scala tympani 
2- Vestibular membrane 
3- Organ of Corti 
4- Basilar membrane 
5- Spiral ligament 
6- Cochlear nerve + spiral ganglion 
7- stria vascularis ( blood supply )

Question 12

Which chambers are linked at the end of the cochlea (Helicotrema )

Answer 12

Scala tympani and vestibuli

Question 13

What is the purpose of the round window

Answer 13

Allows free vibration of the Scala vestibuli and tympani

Question 14

Vibration in the stapes results in what ?

Answer 14

Vibration in the basilar membrane of the cochlea

Question 15

What is the cation in Scala tympani and vestibuli

Answer 15

Sodium

Question 16

What is the cation in the Scala media

Answer 16

Potassium

Question 17

Where is the basilar membrane

Answer 17

Membrane between organ of cortisones and the Scala tympani

Question 18

Explain what happens to movement of the oval window from the Stapes bone

Answer 18

1- Transmitted to scala vestibuli and scala media
2- Vibrate the basilar membrane
3- Rod of corti attached to the basilar membrane will vibrate = inner/outer sensory hair cells attached will move vertically and basilar fibre attached will move laterally
4- Hair cells will induce an AP in cranial nerve 8

Question 19

What does the organ of cortisones consist of and what is it’s purpose e

Answer 19

1- basilar membrane 
2- 1 row of inner hair cells 
3- 3-4 rows of outer hair cells 
4- tectorial membrane 
5- reticular lamina 
6- rods of corti 
Function : convert mechanical signals to nerve signals

Question 20

What is the purpose of the inner and outer hair cells

Answer 20

Inner : Transducers

Outer: modulators ( of frequency ,moderate sound we are hearing )

Question 21

What are the hair cells in the cochlea made of

Answer 21

Rows of stereocilia , with filaments linking one hair cell to another

Question 22

What is the purpose of the filaments in the hair cells of the cochlea

Answer 22

Filaments opens ion channels allowing potassium into the hair cell = depolarizes it.
Neurotransmitter is released which creates an AP in the 8th cranial nerve

Question 23

How do we detect low and high notes ?

Answer 23

The basilar membrane end closest to oval window is stiff and narrow , and on the opposite end ( helicotrema ) it is wide and floppy. This means that each part of the membrane vibrates maximally for different frequencies.
High frequency: displace hair cells near oval window
Low frequency: displace hair at helicotrema

Depending on which hair cells displace , the Brian is sent signals

Question 24

Where do High frequency sounds resonate

Answer 24

Near oval window

Question 25

Where do low frequency sounds resonate

Answer 25

Near helicotrema

Question 26

What is loudness determined by

Answer 26

The number per second of hair cell action potentials

Question 27

What is our threshold of hearing and when can sound begin to cause damage

Answer 27

Threshold : 10 decibels

Sustained exposure of 90+ decibels may cause damage

Question 28

How do we know the direction of sound

Answer 28

Above 3000 Hz it’s loudness difference. if the voice is from the right side it will be louder in the right ear & vice versa

Below 3000 Hz it’s timing difference. if sound is coming form the right it would reach the right ear first

Question 29

Where is the auditory cortex

Answer 29

Superial temporal lobe embedded in the Sylvia fissure

Question 30

What does the auditory cortex consist of

Answer 30

Primary area: tonotopic map of the basilar membrane , high frequency coded for posteriorly , low frequency coded for anteriorly , columns to figure out direction of sound
Association area : Wenicke’s area & brocca’s area

Question 31

What is Wernicke’s & Brocca’s area purpose

Answer 31

Translates language and sounds and then transfers to Brocca’s area which forms a response which is sent to motor cortex

Question 32

What is fluent/receptive aphasia

Answer 32

Damage to Wernicke’s area, can’t understand

Question 33

What is expressive/non-fluent aphasia

Answer 33

Damage to Brocca’s area , can’t make speech in response

Question 34

What is the purpose of the vestibular system

Answer 34

• Maintaining stiffness in the neck muscles ( keeping head on body )
• Righting reflex
• vestibular ocular reflex ( eye following a target and then flicking straight ahead )
• feedback to motor system ( cerebellum )

Question 35

What controls the VOR reflex

Answer 35

The semi circular canals

Question 36

What does the Vestibule System consist of

Answer 36

Inner Ear:  
1- Vestibule: Linear acceleration
- Utricle : horizontal 
- saccule: vertical 
2- 3 semi-circular canals: rotational acceleration planes

Question 37

What is the semicircular canal made of

Answer 37

1- Ampulla at the base ( liquid carving vessel )
2- Cristae ampularis : converts vibrations to signals
3- Capula : hair cells in gelatinous mass

Question 38

Explain the hair cells in the semicircular canals

Answer 38

Kinocilium is a stif hair cell and stereo cilia are hair cells placed after.
Hair cells moving towards kinociulium increases firing rate and vice versa.
Movement facilitated by Potassium.

Question 39

Explain Rotation in terms of the vestibular canal

Answer 39

When head rotates the semicircular canals which are fixed in the skull also rotate. But the fluid within it due to inertia stays in the same place. This causes displacement in the cochlea which causes hair cells to move away or towards the kinocilium , depending on direction of rotation.

Start of rotation : increase of firing rate
End of rotation : decrease of firing rate

Question 40

Where is the signals from the vestibular system sent to

Answer 40

1- Sent to cerebellum to preform predictive movement and provide balance
2- into the spinal cord via vestibulospinal tract for balance and equilibrium
3- Reticular formation for sensing and arousing motor pool
4- Info sent to equilibrium cortex in Sylvia tissue

Question 41

What is Nystagmus

Answer 41

Maintaining visual fixation on a target despite moving

Question 42

What is responsible for motion sickness and dizziness

Answer 42

Conflicting signals between vestibular and visual systems ( especially if there is no acceleration )