Physiology of Hearing and Balance

Question 1

What parts of the ear are involved in hearing and what parts are involved in balance?

Answer 1

The external and middle ear are only involved in hearing, particularly the transmission of sound (vibrations further into the ear).

The inner is responsible for both hearing and balance.

Question 2

What role does the auricle or pinna play in hearing?

Answer 2

The shaped of the auricle helps to essentially capture the sound vibrations and transmit them into the External Auditory Meatus.

Question 3

What is the function of the auditory ossicles of the middle ear?

Answer 3

They are required to amplify the vibrations from the tympanic membrane in order to stimulate the movement of fluid in the inner ear. Beause fluid is harder to move than air.

Question 4

How do the auditory ossicles carry out their function of sound amplification?

Answer 4

The vibration of the tympanic membrane is transferred to the malleus, which has an attachment to the tympanic membrane. The malleus is then attached to the incus and stapes. The stapes is attached to the superior oval window for the transmission of the vibration into the fluid of the inner ear.

Question 5

Within the inner ear, where does the hearing function occur?

Answer 5

The hearing function occurs in the spiral shaped cochlea.

Question 6

Generally outline the anatomy of the cochlea.

Answer 6

The cochlea consists of three main chambers that run all the way through it, separated by sensitive membranes (basilar membrane and the organ of Corti)

The main chambers are the scala vestibuli and the scala tympani (same tube just different folds).

Question 7

What is the basilar membrane?

Answer 7

This is a stiff band of tissue that runs between the scala media and the scala tympan.

Question 8

What does the basilar membrane do?

Answer 8

The basilar membrane is capable of hearing every sound within the human range of hearing and communicating that immediately to the nervous system. Through the use of the Organ of Corti, which have special sensory cells.

Question 9

How does the basilar membrane differential between different frequencies?

Answer 9

Specific movement of the fluid causes sections of the basilar membrane to vibrate back and forth. This membrane is covered by more than 20,000 fibres which range in size from very short and stiff to very long and motile, the length of these increases the further down the membrane you go.
These different length fibres resonate at different frequencies. Short fibres vibrate in response to high frequencies, areas with longer fibres resonant with lower frequencies.

Question 10

How does the organ of corti become stimulated?

Answer 10

Transduction of sound occurs when part of the membrane moves and “tickles” the organ of Corti. The organ of Corti is filled with “hair cells” when these hairs are triggered there is an influx of Potassium through the opening of Potassium channels. Which leads to the formation of graded potentials which may lead to the formation of actions potentials.

Question 11

What is the difference of the inner hair cells and outer hair cells of the organ of corti?

Answer 11

Inner hair cells send most of the message, whereas the outer hair cells are fine tuners, preventing distortion of the sound.

Question 12

Where does the electrical impulses generated by the organ of corti go?

Answer 12

The electrical impulse generated travel from the organ of Corti up the cochlear nerve, up the auditory pathway to the cerebral cortex, to get made of sense of by the brain.

Question 13

What are some of the ways in which hearing can be assessed?

Answer 13

Clinical testing
Tuning fork tests
Audiometry
Objective testing

Question 14

What is Pure Tone Audiometry?

Answer 14

Classic hearing test
Trying to find the lowest sound that a person can hear (different pitches, frequencies and volumes) – the lowest sound = threshold of hearing

Question 15

What does normal hearing tests indicate in terms of the hairs of the inner ear?

Answer 15

Indicates that these hairs are healthy/normal

Question 16

What occurs if there is “hair cell” damage within the ear?

Answer 16

Hearing loss

Question 17

What is the impact of the audible frequencies someone can hear in Presbyacusis?

Answer 17

Presbyacusis is the impact of old age on hearing. Drops in the amount of higher frequencies heard.

Question 18

If the bone conduction is greater than the air conduction what is this?

Answer 18

Conductive hearing loss.

Question 19

Generally outline an Auditory Brainstem Response hearing test.

Answer 19

Essentially a test that measures brainwave activity in response to sound. Usually used in newborns and young children so assess hearing.

Question 20

How can hearing loss be managed?

Answer 20

Surgery (usaully external and middle ear) 
Sound amplification (use of hearing aids) 
Direct stimulus of cochlear nerve cells (cohclear implant in very deaf)

Question 21

Generally outline how a Hearing Aid works.

Answer 21

Sound goes in speaker, is amplified and is sent down the ear hook and into the ear mold.

Question 22

When is the use of a Bone Anchored Hearing Aid indicated?

Answer 22

Used if someone has no outer ear, or is prone to hearing aid infections.

This hearing aid is screwed into the skull, with a processor which receives the sound waves.

Question 23

How does a middle ear implant work?

Answer 23

Sound is collected and trasnferred right through to the ossicles – lets them vibrate more = more direct route

Question 24

Where is a cochlear implant places and generally out does it work?

Answer 24

Put through the mastoid and middle ear – curls around the cochlea and receives impulses.

Question 25

Generally outline how balance occurs in the inner ear.

Answer 25

Uses a series of sacs and canals in the inner ear known as the vestibular apparatus.
This is also a combination of fluid and sensory hair cells. However, the fluid here is controlled through the movement of the head rather than vibrations.

Question 26

What are the semicircular canals?

What are the otolith organs and what is the result of the calcium carbonate crystals being present here?

Answer 26

There are 3 semicircular canals which sit in the frontal sagittal and transverse planes, based on the movement of fluid inside the canals, due to the movement of the fluid we can detect the movement of the head.

In the otolith organs (linear accelerators) – the cilia sit in a big gel matrix – on top of that are otoliths (calcium carbonate crystals) - makes it quite heavy and therefore you need a lot of force to make the cilia move

Question 27

What are the function of the utricle and saccule?

Answer 27

Utricle and saccule – linear accelerator pickups – tell you forwards backwards side to side and up and down

Question 28

How are nerve signals transmitted from the movement of the fluid and where does the impulse go

Answer 28

As the fluid moves – pushes against the cilia – opens ion channels, depolarisation and message goes through the vestibular nerve.

Question 29

What is the vestibulo-ocular reflex?

Answer 29

The VOR stabilises gaze by moving eyes in order to compensate for head and body movement. This fixes image on retina for clear sight.

Question 30

How does the vestibulo-ocular reflex occur?

Answer 30

Semi-circular canals tell you that you are moving but also control our gaze – allow you to control head/eye movement.

Ear communicates with the nucleus of the eye muscles – gets the eye muscles to move in an exact pattern

Question 31

What are the other inputs of balance in the body?

Answer 31

Visual input used in balance – especially when you are moving

Proprioception – important for stabilisng joints

Question 32

What are some of the clinical conditions of the inner ear that affect balance?

Answer 32

Benign Paroxysmal Positional Vertigo
Vestibular Neuritis - labrynthitis
Meniere’s Disease

Question 33

What is the common clincial condition outside of the ear that affects balance?

Answer 33

Migraine